TEKS 7.6 A & BThe Force is with You!

TAKS Objective 4 – The student will demonstrate an understanding of motion, forces, and energy.

Learned Science Concepts

Unbalanced forces cause changes in the speed or direction of an object’s motion.

TEKS 7.6 Science conceptsThe student knows that there is a relationship between force and motion. The student is expected to:

(A) demonstrate how unbalanced forces cause changes in the speed or direction of an object's motion; and

(B) demonstrate that an object will remain at rest or move at a constant speed and in a straight line if it is not being subjected to an unbalanced force; and

OverviewIn this unit, students will have opportunities to examine, measure, reflect upon, and discuss how forces of various origins are used to produce motion. The heart of this unit should be in encouraging students to look for regularities or patterns in motion and in the forces which influence motion. To analyze what we often take for granted is a difficult but useful task. It requires that we look at things from a different perspective and consider what we may previously have overlooked.

Though motion and forces are observed and experienced everyday, few people have a clear understanding of the phenomena. In this section, students will identify forces as balanced or unbalanced and explain how unbalanced forces produce a change in motion while balanced forces do not.

Students will also be introduced to simple machines. They will learn to identify the six simple machines and demonstrate how forces are applied to them and multiplied by them to produce motion.

Instructional StrategiesHands-on activities will involve discovery, inquiry, and experimentation. Activities will include pictures to help recognize and identify the simple machines. Teacher demonstration will be used to illustrate balanced and unbalanced forces. Students will then use hands-on activities to discover how forces interact to produce motion, inquiry to construct balanced levers, and hands-on activities to show how pulleys multiply force.Students will begin studying linear motion in a nearly frictionless environment. They will apply a force and measure results. They will next look at unseen forces due to air resistance.

Objectives1. The learner will identify forces that produce motion.

2. The learner will distinguish between balanced and unbalanced forces.

3. The learner will identify the six types of simple machines from pictures of everyday tools.

4. The learner will identify where forces are located in using simple machines, and where the critical force occurred to produce motion.

5. The learner will use a pulley to demonstrate how simple machines multiply force.

6. The learner will explain how force produces motion in levers, pulleys, and other simple machines.

7. The learner will demonstrate how unbalanced forces produce motion by building a Rube Goldberg machine.

For Teacher’s Eyes OnlyConcepts & Vocabulary

Force- a push or a pull

Balanced forces- forces that are equal in size and opposite in direction. The net force is zero.

Unbalanced forces- Forces that produce a change in motion. The net force is greater than zero.

Net force- The sum of the forces acting on an object.

Motion-Change in position.

Friction- force when two surfaces touch=always in opposite direction of motion.

Inertia- tendency of an object to resist any change in motion.

Newton’s first Law of motion- An object in motion stays in motion at the same speed in a strait line, unless acted upon by an unbalanced force.

We use forces every day to carry out the activities of life. We walk, run, drive cars, open jars, push doors open and pull them closed, brush our teeth, eat, drink, stand, and sit.

A force is a push or a pull. Forces can cause objects to start moving, stop moving, change their motion, or do nothing at all. Forces occur in pairs and can be either balanced or unbalanced. Balanced forces do not cause a change in motion. They are equal in size and opposite in direction. Unbalanced forces cause something to either change speed or change direction.

If you have ever witnessed an arm wrestling competition you have probably seen an example of both balanced and unbalanced forces. If the two opponents are just about as strong as each other, their arms will remain in a vertical position not moving one way or the other. The forces in this instance are balanced forces. The force exerted by each person is equal, but they are pushing in opposite directions, in this case against each other. It would look something like this.

Because the two forces pushing against each other are equal, they cancel each other out and the resulting force (called a “net force”) is zero. Therfore, there is no change in motion.

If, however, the two opponents are a body builder and an average student, then in all likelihood, the body builder would quickly force the student’s arm down toward the table causing a rather quick and probably embarrassing display of hormone deficiency. In this case the forces are opposite but not equal. The two forces combine and the

difference between them produces motion in the direction of the larger force. Unlike balanced forces, unbalanced forces always cause a change in motion. The diagram of that competition would look like this.

= Unbalanced forces can also be exerted in the same direction. For example, if your

car dies in the middle of the road, one person might not be able to push it, but two people pushing in the same direction would increase the force enough to produce the motion needed to get the car off the road. The two forces are added together in the same direction the force if being applied. That scenario would look something like this.

+ =

To sum it up, forces in the same direction always combine by addition and forces in opposite directions always combine by subtraction. Balanced forces are always in opposite directions. They are equal, so the net force acting on the object is zero and so nothing starts moving. Unbalanced forces may be in the same direction of in opposite direction. They produce a net force greater than zero and the resulting response is a change in motion. The object could start moving, stop moving, or change speed and/or direction.

Forces are used in simple machines. Simple machines are machines that produce only one type of motion. They are used to change the size or direction of a force. There are six types of simple machines: the lever, the pulley, the wheel and axle, the inclined plane, the wedge, and the screw. Definitions of each are listed below.

1. Simple machine- a device that uses only one kind of motion to multiply a force. The six simple machines are a lever, an inclined plane, a wedge, a screw, a wheel and axle, and a pulley.

2. Lever- a simple machine consisting of a bar that pivots around a fixed point, called a fulcrum; there are three classes of levers, based on where the input force, output force, and fulcrum are placed in relation to the load: first class levers, second class levers, and third class levers.

3. Inclined plane-a simple machine that is a strait slanted surface; a ramp4. Wedge- a simple machine that is a double inclined plane; a wedge is often used

for cutting.5. Screw- a simple machine that is an inclined plane wrapped around in a spiral

around a central core.6. Wheel and axle- a simple machine consisting of two circular objects of different

sixes; the wheel is the larger of the two circular objects.7. Pulley- a simple machine that consists of a grooved wheel that holds a rope or

cable.(Holt Science and Technology, Holt, Rinehart, and Winston, 2001)

Each type of simple machine is capable of giving mechanical advantage. In other words, it can take the force applied to the machine and multiply it. You would find it very difficult ot open a can of paint with your bare hands. A lever, however, makes the job much easier by multiplying the force your hand applies. Although the work is easier, the amount of work done is not changed. Work equals force x distance.

Whenever, the force decreases, the distance increases proportionately so the work done never changes.

Student Misconceptions Misconception

A force is necessary to keep a body moving.

Science ConceptIn fact, the opposite is true. It is often the contrary force of friction that causes objects to slow down and eventually stop. If no force is exerted on a body then it will continue to move as it did before.

Rebuild ConceptShow an object in motion in (nearly) frictionless condition. Let students discuss or experiment with keeping the object in motion (add no force) and stopping the object (apply a force).

MisconceptionIf an object is sitting still (is at rest) there are no forces acting on it.

Science ConceptThe statement is almost right: if an object is at rest there are no unbalanced external forces acting on. There can be very many and very large forces acting on an object sitting still, but they all balance out.

Rebuild ConceptConsider a very large balancing boulder. The rock is sitting still but the weight of the rock is pushing very hard on the rock underneath it. Meanwhile, the rock underneath is pushing back up with exactly the same force and in the opposite direction, so the forces, even though they are very large, are balanced out. If the

rock beneath fails to provide the balancing force, then the balancing boulder becomes a rolling stone.

MisconceptionThe influence of a force continues to be felt even if the force is not acting on the object.

Science ConceptThe speed and/or the direction of the overall motion of an object change when and only as long as a force exerts itself on the object. When the force is “turned on” the body speeds up, slows down and/or changes direction. When the force is “turned off” the object will continue to go in the same direction and at the same speed as it was going the instant when the force was removed.

Rebuild ConceptDiscuss a spacecraft, ignoring gravity acting upon it. What happens when the rockets fire and don’t fire. This concept of motion should be brought up during many different motion activities because it is very hard to dispel the misconception.

Student Prior Knowledge

5 E’s

EngageThe teacher will walk around the room demonstrating balanced and unbalanced forces. Students will then discuss which forces produced motion and why.

The teacher will: 1. Blow on a pinwheel.2. Push the door open.3. Throw a ball across the room.4. Wad up a piece of paper and let it fall from your hand.5. Push against the wall hard as if trying to move it.6. Use a magnet to move a metal object through a desk or poster board.7. Plug up a fan.8. Arm wrestle a student of your own strength.9. Have a double pan balance set up with identical weights that are perfectly

balanced… Add a second weight to one side of the scale.

Explore

Exploration 1Activity: Try and Force Me (Blackline Master)Class Time: 30 minutesObjective 1: The learner will identify forces that produce motion.Objective 2: The learner will distinguish between balanced and unbalanced forces.Activity Overview: Students will observe different kinds of forces. They will determine what the agent, receiver, and affect of each force is.

A force is a push or a pull that one body exerts on another. In the following activity, you will identify what is causing the force in each situation, what the force acts on (the receiver of the force), and what effect the force has on the receiver.

Materials:1 empty glass1 empty cupA pailWaterPaper clipsA magnet2 Plastic strips cut from a bread bag (30 cm long)Wool cloth2 booksString @pieces of paper2 spring scalesSeveral staws2 balloonsPinwheel

Teacher Preparation:

You may set up the room with different stations. The students can rotate through each station as they make observations and fill in their data tables. A timer may be used to move students through at a steady pace or a bell may be rang when students are ready to change places. It should take about 5 minutes per station.

You may instead choose to make all materials available for every group of four students. In that case, you will need the materials above for each group and a space large enough for each group to work.

Stations would be set up as follows:

Station 1: A pail of water and an empty cup.Station 2: An empty glass, several paper clips, and a magnet.Station 3: Bread strips cut from a plastic bread bag and a wool cloth.Station 4: 2 pieces of paper (one wadded up; the other flat)Station 5: A book with a string tied securely around it. Attach a paper clip to the string on one end and fasten the other end of the paper clip to the hook on a spring scale.Station 6: Set up exactly as station 5, but include several straws on the table.Station 7: One slightly inflated balloon; one fully blown up balloon.Station 8: 2 Pinwheels (one large; one small)

ElaborateActivity: Finding Your Balance (BLACKLINE MASTER: Data Table – Finding Your Balance)

Class Time: 20 minutes

Objective: The students will attempt to identify balanced and unbalanced forces from the Explore: Try and Force Me.

ExplainThere are many types of forces: mechanical, electrical, magnetic, gravitational,

friction, buoyancy, ect. A force is simply anything that produces a push or a pull. Your hand pushing the cup down into the water is a force. The water pushing back on the cup was another force. Forces always occur in pairs so when you see one you know there is another somewhere. Pulling the cup up out of the water is countered by gravity pulling the cup back down into the water.

Things don’t have to actually touch to be pushed or pulled. For example, electrical and magnetic forces work by attraction and repulsion. You can feel the pull of a magnet when it nears a piece of iron even though it is not actually in contact with the iron. The bread strips repel each other when electrically charged. The force pair there is the air pushing in on the bread strips as the electrical force pushes them apart.

Friction is a force that opposes motion between two surfaces that are touching. The book being dragged across the table required a pull against the opposite pull of friction between the surface of the book and the surface of the table. Friction is decreased, by making the book roll over the straws.

Air inside the balloon pushes back against the sides of the balloon. When you squeezed the slightly inflated balloon, there wasn’t much air inside to push back so it was easy to squeeze. The inflated balloon had much more air inside to push back against the walls of the balloon so it was much harder to squeeze.

Finally, the large pinwheel will turn more slowly than the small one with the same force of air being blown across it. Being bigger, more air will push against it than the small one.

EvaluateVisual Assessment: The teacher will rub a balloon with wool for 30 seconds. Then the balloon will be placed near tiny pieces of paper (.5 cm pieces of tissue work well) laying on a table. The balloon should pick up the paper pieces without actually touching them if held an inch or two away. Some or all of the pieces should release in a short time as the students watch.

Instruct the students to:

1. Make observations.2. Explain what happened in terms of forces.

They should be sure to include the following:

1. Detailed observations.2. Inferences based on observations.3. Identify the forces at work.4. Identify the forces as balanced or unbalanced during each change in motion.

Sample Answer:The wool cloth gave the balloon an electrical charge. The electrical force pulled

the pieces of paper to the balloon when held near. The electrical force on the balloon was greater than the gravity holding the paper on the table and so the paper moved toward the balloon due to these unbalanced forces. The paper remained stationary on the balloon for a moment as the forces balanced then the force of gravity became stronger than the electrical force which was steadily leaving the balloon. At the point the forces once again became unbalanced, the paper fell back down.

EngageThe teacher will read this entertaining story of a real accident report to introduce

forces in simple machines. It was published by Charles Allbright of the Arkansas Traveler.

“I am writing in response to your request for additional information. In Block Number 3 of the Accident Reporting Form I put ‘trying to do the job alone’ as the cause of my accident. You said in your letter that I should explain more fully.

I am a brick layer by trade. On this day I was working alone on the roof of a new six-story building. When I completed my work, I had about 500 pounds of bricks left over. Rather than carry them down by hand, I decided to lower them in a barrel by using a pulley, which fortunately was attached to the side of the building. (This was no routine procedure).

“Securing the rope at ground level, I went back up and loaded the bricks into the barrel. Then I returned to the ground and untied the rope, holding it tightly to slow the descent of the 500 pounds of bricks. You will notice in Block 11 of Accident Reporting Form that I weigh 135 pounds. Now follow closely.

“Due to my surprise at being jerked off the ground so suddenly, I lost my presence of mind and forgot to let go of the rope. I proceeded at a rather rapid rate up the side of the building. Near the third floor I met the barrel coming down. This explains the fractured skull and broken collar bone. (Shooting upward, the victim never slowed down until his right hand disappeared two-knuckles deep into the pulley.)

“I was able to hold tightly to the rope in spite of my pain. At about the same time; however, the bricks hit the ground and the bottom fell out of the barrel. Devoid of the weight of bricks, the barrel now weighed about 50 pounds. I refer you again my weight in Block 11. As you might imagine, I began a rapid descent down the side of the building.

“In the vicinity of the third floor I met the barrel coming up. This accounts for the two fractured ankles and lacerations on my legs and lower body. The encounter with the empty barrel slowed me enough to lessen my injuries when I fell into the pile of bricks and, fortunately, only three vertebrae were cracked.” We should all count our blessings. Crashing into a pile of bricks ended the accident. But not quite.

“I am sorry to report that as I lay there on the bricks in pain, unable to stand, and watching the empty barrel six stories above me, I again lost presence of mind. I let go of the rope. The empty barrel weighed more than the rope so it came back down on me and broke both of my legs.” Which comes to the report.

“I hope I have furnished the information you require as to how the accident occurred.”

ExploreExploration 1

Activity: Keep it Simple! (Blackline Master)Class Time: 20 minutesObjective: The learner will identify the six types of simple machines from pictures of everyday tools.Activity Overview: Students will read the descriptions of the six simple machines and place pictures of simple machines into categories.

Websites:http://www.mikids.com/Smachines.htmwww.sirinet.net/~jgjohnso/inclineplanecolored.jpgwww.sanwich.k12.ma.us/webquest/machines/can.jpgwww.lhup.edu/.../scenario/labman1/pulleyss.gifwww.school-forchampions.com/.../machines4.gif

Exploration 2

Activity: Name That Force! (Blackline Master)Class Time: 20 minutesObjective: The learner will identify where forces are located in using simple machines, and where the critical force occurred to produce motion.Activity Overview: Students will assemble in groups of three or four and answer the following questions:

1. In each of the pictures, tell what forces are involved to produce motion.2. Explain where the force in each picture is applied to produce motion.3. Explain where the critical motion takes place in each picture.

ElaborateElaboration 1

Activity: Just Hangin’ Around (Blackline Master)

Class Time: 40 minutesObjective: The learner will build a mobile made out of balanced levers.

The students will make a mobile out of balanced levers.

Preparation: You will need the following materials per group:-String-4 wooden dowel rods (one 50cm long, the others at various shorter lengths)-Various objects of different weights (paper clips, keys, construction paper figures with coins attached by glue or tape, etc.)-Spring scale calculated in newtons.

Answer to Challenge Question: You can insert any value into A and B as long as A times the effort (2 m) equals B times the resistance arm (8 m). The product of the resistance arm and resistance force must equal the product of the effort arm and effort force. If B is 2, then 2(resistance force) x 8 (resistance arm) = 16. The product of the effort arm and effort force must also be 16, so A would have to be 8. The total effort force hanging from the top arm of 4m would be: 100 + 20 + 8 + 2 = 130. The product of 130 (total effort force) x 4 m (effort arm at the top) = 525. Therefore the resistance arm (8 m) x the resistance distance must equal 525. (8 x resistance force = 525) 525 8 = 65, so C is 65 kg.

Elaboration 2

Activity: Pull Me Up! (Blackline Master)Class Time: 50 minutesObjective: The learner will use a pulley to demonstrate how simple machines multiply force.Activity Overview: Students will use a simple fixed pulley, and a block and tackle to compare how pulleys multiply force.

Data Table – Pull Me UP!

Mass of object Resistance force Effort force

1. How does the amount of force being lifted compare to the amount of force required to lift it?

2. When were forces balanced? When were they unbalanced?3. What was the effect of unbalanced forces?

ExplainPulleys are used to make work easier. They do this by either changing the size or the direction of the force. In this activity, only the direction of the force was changed. A single, fixed pulley does not multiply force. The force on the pulley rope would have to be a little greater than the force being lifted in order to move it. At any point you could suspend the mass in the air and stop pulling down on the rope. Then the forces would be balanced. However, to continue to raise the mass, a slightly greater force would have to be applied. The forces in this case are very close to equal. If you had used a moveable pulley (2 supporting strands) or a block and tackle (multiple supporting strands) the force required to lift the mass would have decreased but the length of rope needed would have increased.

Elaboration 3

Activity: Rube Goldberg machine (Blackline Master)Class Time: 50 minutesObjective: The learner will construct examples of the six simple machines.Activity Overview: Students will assemble a Rube Goldberg machine given insturtions.

Ruben Lucius Goldberg (1883-1970) was a famous American cartoonist in the early part of the 20th century. He was widely known for his humorous drawings that showed many simple machines linked together in unusual or ridiculous ways usually to accomplish a simple task. These apparatuses became known as Rube Goldberg machines. Goldberg received the Pulitzer Prize in 1948 for his editorial cartooning.

The students will be given instructions to assemble a Rube Goldberg machine. (See Blackline Master Elaboration 3 “Simply Stupid”.) It will include all six simple machines and accomplish one simple task of raising a flag.

The students will construct a Rube Goldberg Machine. It must include an example of all six simple machines and must accomplish a simple task of the students’ choice.

Elaboration 4Rube Goldberg Machine (Blackline Master)You may choose to do this as a project at home. It is very challenging and comes with a rubric for easy grading.

Ruben Lucius Goldberg (1883-1970) was a famous American cartoonist in the early part of the 20th century. He was widely known for his humorous drawings that showed many simple machines linked together in unusual or ridiculous ways usually to accomplish a simple task. These apparatuses became known as Rube Goldberg machines. Goldberg received the Pulitzer Prize in 1948 for his editorial cartooning.Your assignment is to build a Rube Goldberg machine that contains at least one example of all six simple machines and accomplishes a simple task.

Objective:

Build a machine that contains at least one example of all six simple machines.

Your machine must accomplish one simple task.

Your machine cannot be more than 50 cm in any direction.

Rules:

You may not use parts from any game designed to be a Rube Goldberg such as Mouse Trap.

You may not use any electric or battery-operated devices.

The machine must not contain any dangerous parts such as explosives, fire, or firecrackers.

Once you put the machine in motion, you may not touch it in any way to accomplish the simple task you have selected. It must continue by its own action.

Materials:

StringWood

WaterPaper cupsIron washesGlueDrinking strawsWireSpoolsTubesAnything else that falls within the guidelines of the rules

Rubric

Each simple machine is represented (10 points each) 60 _______ Machine accomplished the simple task 50 _______Machine did not exceed the size limitation 50 _______Diagram of machine 40 _______

Total Points 200 _______

Evaluation From the Rube Goldberg machine constructed with instructions, the students will identify the six simple machines and explain how they work to produce force and motion.

Try and Force Me!Exploration 1

A force is a push or a pull that one body exerts on another. In the following activity, you will identify the force in each situation, what the force acts on (the receiver of the force), and what affect the force has on the receiver. Make observations and fill in your data table as you go.

Procedure:Station 1:

1. Hold the empty cup right side up and slowly plunge it down into the water just until the water slowly enters the cup.

2. Lift the filled cup out of the water. Do this several times with your eyes closed allowing yourself to identify the forces at work.

3. How do the forces change as you push the cup further down into the water (before the water comes in)?

4. How do the forces change as the water enters the cup?5. How do the forces change as you lift the cup out of the water?6. Now turn the glass upside down. Slowly plunge the glass all the way to the

bottom of the pail, then lift it strait back up out of the water, feeling the forces as you go.

7. How do the forces change as you move deeper into the pail? As you come back up?

Station 2:1. Place the paper clips under the inverted empty glass2. Using the magnet, try to pull the paper clip up to the top.3. Now lift the glass off the table.4. Can the magnet act through the glass?5. Do you think magnets can act through any other substances? Name some.

Station 3:1. Pick up two bread strips. Hold the ends of the two strips together and let them

hang freely. What do you observe?2. Now take each strip separately, and holding the strip with a piece of wool cloth,

pull it through the wool. (This will rub both sides of the strip with the wool cloth.) Hold the strips together at one end again letting the ends hang freely. What do you observe now?

3. Hold your hand in the middle of the two strips. What happens?

Station 4:1. Hold a flat piece of paper at your waist. (Paper is parallel to the floor) Let it fall.2. Now hold a wadded up piece of paper at your waist and let it fall.3. Let the pieces of paper fall at the same time. Which one falls the fastest?4. Can you think of a way to change the rate of fall?

Station 5:1. Place the book with the string around it on one end of a table.2. Hook a spring scale to the string around the book and slide it across the table at a

constant speed.3. How much force was needed to pull the book?

Station 6: 1. Place the book at one end of the table. Put several straws under the book spaced

out in even increments.2. Attach the spring scale to the string around the book and pull it at a constant speed

across the table.3. How did the force needed to pull the book on straws compare with the force

needed to drag the book in station 5?

Station 7:1. Squeeze the slightly inflated balloon with one hand.2. What causes the balloon to change shapes?3. Gently squeeze the fully inflated balloon.4. How do the forces needed to squeeze the balloon with just a little air compare to

the forces needed to squeeze the fully inflated balloon?

Station 8:1. Blow gently on the large pinwheel.2. Blow gently on the small pinwheel.3. Is there a difference in the force needed to blow the large on compared to the

small one?4. Can you tell if there is a difference in the number of spins on the large pinwheel

compared to the small one if the blow force is the same?

Data Table - Try and Force Me! (Exploration 1)

Station Agent of force Receiver of force Effect of force(1) Cup right side up.

(1) Cup upside down.

(2)

(3)

(4) Wadded paper.

(4) Flat paper.

(5) Book w/o straws.

(5) Book with straws.

Finding Your BalanceExploration 2

Forces always occur in Pairs. The pairs are either balanced or unbalanced. Balanced forces do not produce any change in motion but unbalanced forces do. Based on your observations in the Exploration 1 Activity, “Try and Force Me!,” see if you can identify whether or not the forces were balanced or unbalanced, whether or not the forces produced a change in motion.

Station 1:

Balanced forces:

Unbalanced forces:

Station 2:

Balanced forces:

Unbalanced forces:

Station 3:

Balanced forces:

Unbalanced forces:

Station 4:

Balanced forces:

Unbalanced forces:

Station 5:

Balanced forces:

Unbalanced forces:

Station 6:

Balanced forces:

Unbalanced forces:

Station 7:

Balanced forces:

Unbalanced forces:

Station 8:

Balanced forces:

Unbalanced forces:

Keep It Simple!Exploration 1 (page 1)

Using the information below, cut out each picture and glue it under the correct type of simple machine.

1. Simple machine - a device that uses only one kind of motion to multiply a force. The six simple machines are a lever, an inclined plane, a wedge, a screw, a wheel and axle, and a pulley.

2. Lever- a simple machine consisting of a bar that pivots around a fixed point, called a fulcrum; there are three classes of levers, based on where the input force, output force, and fulcrum are placed in relation to the load: first class levers, second class levers, and third class levers.

3. Inclined plane -a simple machine that is a strait slanted surface; a ramp4. Wedge - a simple machine that is a double inclined plane; a wedge is often used

for cutting.5. Screw - a simple machine that is an inclined plane wrapped around in a spiral

around a central core.6. Wheel and axle - a simple machine consisting of two circular objects of different

sixes; the wheel is the larger of the two circular objects.7. Pulley - a simple machine that consists of a grooved wheel that holds a rope or

cable.

1 2 3

4 5

6 7 8

9 10 11

12 13 14

15 16

17 18

19 20

Glue each picture under the correct category of simple

machine.Lever Pulley Wheel

and axleInclined Plane Wedge Screw

Name That ForceExploration 2

A B

C D

E F

Using the pictures above, answer the following questions:

1. In each of the pictures, tell what forces are involved to produce motion.2. Explain where the force in each picture is applied to produce motion.

3. Explain where the critical motion takes place in each picture.

Data Table: Name That Force (Student Worksheet #1)

Picture Forces involved to produce motion

Where force is applied to produce motion

Where critical motion takes place

A

B

C

D

E

F

Just Hangin’ AroundElaboration 1

A lever is a bar that is free to pivot on a specific point. The point the bar pivots on is called the fulcrum of the lever and the bar on either side of the fulcrum becomes the arms of the lever.

Effort arm Resistance arm

Fulcrum

When a force is applied to one of the arms, it is capable of lifting a load carried by the other arm. Mathematically, if you multiply the load (called the resistance force) by the length of the arm carrying the load (called the resistance arm) it will equal the product of the effort applied to the other arm (the effort force) and the length of that arm (effort arm). This is known as the “Law of the Lever” and the equation looks like this:

resistance force x resistance arm = effort force x effort arm

You can make a mobile made up of levers. The levers will be dowel rods hanging from string. The point at which the string is attached will be the fulcrum of each lever. The dowel rod on either side of the string will be the arms of the lever. The distance between the object and the fulcrum (string holding the dowel rod up) is the effort arm and the distance between the object on the other side and the fulcrum is the resistance arm. If the rods hang at a perfect horizontal to the floor, the levers will be balanced and according to the Law of the Lever. The length of the effort arm x the effort force (weights or objects hanging from that arm) will equal the length of the resistance arm x the resistance force (weights or objects hanging from that arm).

Objective: You will construct a mobile made up of balanced levers and prove mathematically that the levers are balanced.

Materials:1. String 2. 4 wooden dowel rods (one 50 cm long, the others at various shorter lengths)3. Various objects of different weights (paper clips, keys, construction paper figures

with coins attached by glue or tape, etc.)4. Spring scale calculated in Newtons

Procedure:

1. Find a place to anchor your mobile such as a ring stand or table top.2. Weigh each object as you place it in your mobile (including the dowel rods) record the weights in Data #1.3. Using a string, attach the 50 cm dowel rod to the anchor.

4. You may make the mobile using any design. The only criterion is that each lever must be balanced horizontally. (See Figure 1)

5. When you have successfully constructed your mobile, measure the length of all your arms and record them in Data Table #2. (Choose one arm as the effort arm and the other as the resistance arm) Be sure you have also entered all weights into the data table. The weight hanging from the effort arm is the effort force and the weight hanging from the resistance arm is the resistance force.

Figure 1

Data Table #1Just Hangin’ Around

Elaboration 1Object Weight in Newtons

Data Table #2Just Hangin’ Around

Elaboration 1Lever Effort

Arm (mm)

Effort Force (N)

Product (N x mm)

Resistance Arm (mm)

Resistance Force (N)

Product (N x mm)

A

B

C

D

Analysis:1. Calculate the products of the effort arms and effort forces as well as the products of the resistance arms and resistance forces.2. What is the relationship between these two products?3. Using the information from data table # 2, explain how your mobile demonstrates the Law of the Lever.

Conclusion:1. If a 30 Newton weight hangs from a 20 cm effort arm, and a 20 Newton weight hangs From a 30 cm resistance arm, is the lever balanced? How can you tell?2. How can you create a balanced lever?

Challenge Question:

Determine the weight of triangle A, circle B, and rhombus C if the above mobile is perfectly balanced.Google Images: www.olemiss.edu/mathed/geometry/mobile.gif

Pull Me Up!Elaboration 2

Objective: To use a pulley to demonstrate how simple machines multiply force.

A pulley is a simple machine consisting of a grooved wheel that holds a rope or cable. It is basically a modified lever in that the rope on each side of the pulley is like a flexible bar that pivots on the wheel fulcrum. Simple machines may either change the size or directions of a force. When a machine changes the size of a force, the distance through which that force travels must also change. It is an indirect proportion. When one increases, the other decreases.

For example, as you tried to lift a box weighting 450 Newtons into the back of a truck one meter off the ground it would be very difficult. If, however, you pushed the box up on inclined plane that was 3 meters long, you would only have to apply a force of 150 Newtons. The force needed to lift the box decreased (1/3 of original force), but the distance the box traveled increased (3 times the original distance).

The number of times your force is multiplied by a pulley depends on the number of supporting stands. If you have a single fixed pulley, there is one supporting strand. A single moveable pulley has two supporting strands. A block and tackle includes both a fixed pulley and a moveable pulley. It may have a number of supporting strands.

You will rig up a single fixed pulley, then tie the free end of your pulley rope to a weight. Lift the weight to the highest possible point and determine where forces are balanced and unbalanced. (See Figure A)

To determine the force required for the lift, attach a spring scale to the free end of the pulley rope and carefully observe the number of Newtons needed, then record this information in your data table.

Materials:1-m length of pulley rope meter stick500g and 1kg masses with hooksWire ties, 10cm and 30cm longSpring scale that measures in NewtonsUtility clamp for ring standRing stand Masking tape Two pulleysMeter stick

Figure A

Procedure: Single Fixed Pulley

1. Clamp the utility clamp to the top of the ring stand. Connect one of the pulleys to the utility clamp using the wire tie.

2. Tape the meter stick vertically to the rod of the ring stand.3. Tie a small loop in each end of the pulley rope. Attach one looped end to the

spring scale and the other looped end to the 500g mass. What is the weight in Newtons? Record this value in the Data Table . It is your resistance force.

4. Thread the pulley rope around the wheel of the pulley. (One looped end is still hooked to the 500g mass and the other looped end to the spring scale.)

5. With the mass resting on the base of the ring stand, slowly pull straight down with the spring scale to raise the mass up to the pulley. Note the number of Newtons required. This is your effort force. Record this value in the Data Table.

6. Lower the mass to the table and repeat step 5, this time measuring the distance the spring scale moves as you raise the mass 15cm. Record this value in the Data Table. This is your effort distance. 15cm is your resistance distance.

7. Repeat steps 3-6 with the 1kg mass and record your data.

Data Table – Pull Me UP!

Mass of objectbeing lifted

Resistance force(N)

Effort force(N)

Resistance distance (cm)

Effort distance (cm)

500 g weight1 kg weight

1. How does the amount of force being lifted compare to the amount of force required to lift it?

2. When were forces balanced? When were they unbalanced?3. What was the effect of unbalanced forces?

Simply StupidElaboration 3

Materials: Problem: To build a Rube Goldberg machine that includes all six simple machines and whose function is to raise a flag.

1x2 pegboard4 1/4" dowel rods (48” long dowel rods)2 90◦ 2 inch PVC elbow joint1 single fixed pulleys1 heavy sinker13 large craft sticks1 wooden spool that spin freely on a dowel rod1 screw-in cup hook (small enough to screw in a craft stick)3 straws (must fit around ¼” dowel rod)Twine1 golf ball1 plastic cups

1 poster boardHot glue gunScissorsSturdy wire cutter or tool to cut dowel rodsHole punch

Procedure:

You will begin on a corner, 3 holes in from one side and 2 holes in from the other side of the corner.

Pulley stand:Place peg board on a flat surface. Assemble pulley stand. Make four dowel rods 40 cm length (you will have 4 pieces). Place the rods in the peg board 4 holes apart from each other to form a square tower.

Now build a brace for the top of the tower. Cut 2 craft sticks in half. Use a 3 hole paper hole punch to punch holes in the ends of the sticks and glue to

the top of the tower.

With other two halves, stack them on top of each other and glue together at the ends. Then screw a cup hook into the middle of the sticks. When this is assembled, glue the hook and sticks crosswise across the other two sticks of the frame. Be sure the hook is down. Hang the pulley from the hook.

Paddle Wheel:

Cut 8 paddles from craft sticks. Each section needs to be 6.5 cm long. Cut two circles with a 7 cm. diameter using poster board. Poke a hole in the center of each circle large enough for a ¼ inch dowel rod to fit through the hole. Cut a piece of dowel rod 15 cm long and insert it through the center holes of both circles. Spread the circles apart just far enough for the craft stick to be inserted perpendicularly to make the spokes of the wheel.

Cut two dowel rods 20 cm long each. Place them 10 holes from the pulley stand. Cut a section of straw for each end of the paddle wheel axle. Slip the straw sections over the ends of the paddle wheel axle and glue the paddle wheel straw sections to each paddle wheel leg.

Straw section

Wheel axle

Paddles

Golf ball stand:

Cut a piece of poster board 11 cm x 8.5 cm. On the 11 cm side, fold up 3.5 cm on each end.

Cut 4 sections of ¼ inch dowel rod, each 9 cm long. Glue 4 legs to the four corners of the ball holder on the underside. Then place the stand in the peg board centering it under the paddle wheel.

Golf Ball Shoot:

3.5 cm

11 cm

Fold here

The large PVC elbow joint is the shoot. It is held up by 2 stands made as follows. First attach a craft stick to a 10 cm piece of dowel rod. Allow 3 cm of dowel rod to stick out past the craft stick (see picture below). You will need two of these. Place each post in the peg board 4 holes away from the paddle wheel stand. Then place a craft stick as a brace connecting the two posts. To do this, you must first place the elbow joint between the posts and line the opening up with the ball stand so that the golf ball will move directly from the stand into the shoot. Once you find the right location to hold it up at the right height, then glue it in place.

You will need a second support. Place another 10 cm piece of dowel rod 3 holes from the inside arm of the first support. To attach the cross stick, glue a craft stick to the rod so that when the rod is in place, the top horizontal edge of the craft stick will hit the rod 6.5 cm from the peg board. The other end of the dowel rod attaches to the first support exactly under its cross stick.

Ramp:

Cut a 30 cm x 10 cm piece of poster board. Fold up 3 cm on the long sides of the poster board to make a ramp. To attach the ramp, first build a stand to hold the upper section in place. Cut a craft stick in half and place the halves side by side. Glue two braces on the back to hold them together.Glue two 6.5 cm pieces of dowel rod to each brace. Then glue a cross support to the two dowel rods.

Cut the poster board along the fold lines 4 cm from the end of the ramp. Glue the middle section (inside the cuts) of the poster board to the top of the ramp support.

1

2 3

Cut in half.

Use two 10 cm dowel rods and one 11 cm dowel rod to construct the tack lever. Place an 8.5 cm piece of straw over the 11 cm dowel rod. Glue the ends of the 11 cm dowel rod (covered with the straw) to the ends of the 10 cm. dowel rods as shown. Make sure that no glue contacts the straw. Place a a craft stick vertically on the center of the straw and making sure that it will clear the ramp, glue it down to the straw.

Set cup at end of ramp. Position 7 cm dowel rod pieces to secure it. Position a lever at the end of the ramp.

Rube Goldberg MachineEvaluation

Ruben Lucius Goldberg (1883-1970) was a famous American cartoonist in the early part of the 20th century. He was widely known for his humorous drawings that showed many simple machines linked together in unusual or ridiculous ways usually to accomplish a simple task. These apparatuses became known as Rube Goldberg machines. Goldberg received the Pulitzer Prize in 1948 for his editorial cartooning.Your assignment is to build a Rube Goldberg machine that contains at least one example of all six simple machines and accomplishes a simple task.

Focus on Physical Science by Merrill Publishing Company, 1989, 1987, Enrichment – “What is a Rube Goldberg Device?” pg. 254

Your assignment is to build a Rube Goldberg machine that contains at least one example of all six simple machines and accomplishes a simple task.

Objective:

Build a machine that contains at least one example of all six simple machines.

Your machine must accomplish one simple task.

Your machine cannot be more than 50 cm in any direction.

Rules:

You may not use parts from any game designed to be a Rube Goldberg such as Mouse Trap.

You may not use any electric or battery-operated devices.

The machine must not contain any dangerous parts such as explosives, fire, or firecrackers.

Once you put the machine in motion, you may not touch it in any way to accomplish the simple task you have selected. It must continue by its own action.

Materials:

StringWoodWaterPaper cupsIron washesGlueDrinking strawsWireSpoolsTubesAnything else that falls within the guidelines of the rules

Rubric

Each simple machine is represented (10 points each) 60 _______ Machine accomplished the simple task 50 _______Machine did not exceed the size limitation 50 _______Diagram of machine 40 _______

Total Points 200 _______

TEKS 7.6 Science concepts

The student knows that there is a relationship between force and motion. The student is expected to:

B demonstrate that an object will remain at rest or move at a constant speed and in a straight line of it is not being subjected to an unbalanced force; and

OverviewThough motion and forces are observed and experienced everyday, few people have a clear understanding of the phenomena. In this section, students will develop an understanding of forces and motion according to Newton’s First Law by working with “hover pucks”. They will observe that when forces such as friction are virtually eliminated, objects will move at the same speed and in a straight line unless acted upon by another force.

Instructional StrategiesHands-on activities will involve discovery, inquiry, and experimentation. Students will begin studying linear motion in a nearly frictionless environment. They will apply a force and measure results. They will next look at unseen forces due to air resistance.

Objectives8. The learner will apply the laws of motion to real world examples.

9. The learner will identify size and direction of a force.

10. The learner will use equipment to measure time and distance so that the motion of the object can be determined.

11. The learner will use data collected to calculate the speed of an object.

12. The learner will explain the results of applying a force to an object.

For Teacher’s Eyes OnlyConcepts & VocabularyMotion- change in position

Speed- rate of motion = distance / timeDirection of Motion- where object is going- draw a straight line to represent where object was then & nowForce – a push or pull

Equilibrium- all forces balancedFriction- force when two surfaces touch- always in opposite direction of motion

Newton’s 1 st Law

An object in motion stays in motion in a straight line, unless acted upon by net force. An object at rest remains at rest unless acted upon by a net force.

Three laws of motion are attributed to Newton, but we will only look at the first law in this unit. If one really understands Newton’s three laws of motion, no matter what words one uses to articulate them, then much of the ways things move become clear. Otherwise, the world can be a bewildering place in which objects move in seemingly bizarre ways. It is imperative that the student be led to observe and to analyze the way things actually move. The “Laws” of motion are laws only in the sense that they are rules that describe what actually is happening when an object moves. Isaac Newton, about three hundred and twenty years ago (1687), was able to summarize all the essential knowledge of motion in three fundamental rules: Newton’s Laws of Motion.Newton’s First Law of Motion (Xtreem Science version):An unbalanced external force (and only such a force) is what causes an object to speed up, to slow down or to change its direction of motion (that is, accelerate).Some consequences of this rule are:

A. The motion is an overall motion of the object rather than the motion of one part relative to another part.

B. If an object (which must be made of matter to be an object) is motionless to begin with, then it will continue to be motionless (“will remain at rest” as physicists say) indefinitely unless or until it is acted on by an unbalanced external force.

C. A body that is moving will continue to move in a straight line at the same speed unless or until an unbalanced external force acts on the object.

D. If an object is speeding up, slowing down and/or changing the direction of its motion an unbalanced external force is exerting itself on the object.

E. “Acceleration,” as physicists use the word, means that there is a change in the speed (increase or decrease) and/or a change in the direction of motion.

All motion can be understood by three simple rules: Newton’s Laws of Motion. However, they must be applied to particular situations with full attention to identifying all the forces and the masses involved. Our focus in seventh grade is only on the first law.

Student Misconceptions Misconception

A force is necessary to keep a body moving.

Science ConceptA body in motion will remain in motion if no other force acts on it. It is often the contrary force of friction that causes objects to slow down and eventually stop. If no force is exerted on a body then it will continue to move as it did before.

Rebuild ConceptShow an object in motion in (nearly) frictionless condition. Let students discuss or experiment with keeping the object in motion (add no force) and stopping the object (apply a force).

MisconceptionIf an object is sitting still (is at rest) there are no forces acting on it.

Science Concept

The statement is almost right: if an object is at rest there are no unbalanced external forces acting on. There can be very many and very large forces acting on an object sitting still, but they all balance out.

Rebuild ConceptConsider a very large balancing boulder. The rock is sitting still but the weight of the rock is pushing very hard on the rock underneath it. Meanwhile, the rock underneath is pushing back up with exactly the same force and in the opposite direction, so the forces, even though they are very large, are balanced out. If the rock beneath fails to provide the balancing force, then the balancing boulder becomes a rolling stone.

MisconceptionThe influence of a force continues to be felt even if the force is not acting on the object.

Science ConceptThe speed and/or the direction of the overall motion of an object change when and only as long as a force exerts itself on the object. When the force is “turned on” the body speeds up, slows down and/or changes direction. When the force is “turned off” the object will continue to go in the same direction and at the same speed as it was going the instant when the force was removed.

Rebuild ConceptDiscuss a spacecraft, ignoring gravity acting upon it. What happens when the rockets fire and don’t fire. This concept of motion should be brought up during many different motion activities because it is very hard to dispel the misconception.

Student Prior Knowledge

Students should be able to describe the changes in position, direction, and speed that occur when a force acts on an object. (TEKS 6.8 A)) Students should also be able to measure an object’s change in motion and produce a graph from the data. (TEKS 6.8 (B))

5 E’sPush Me, Pull Me, Watch Me Fall

EngageEngage 1

Teacher demonstration:

If you are brave and have practiced, the old tablecloth pulled out from under the dishes is great. Most people however, are not so brave. A safer method is to place a small, smooth card on top of a jar. Then place a coin on top of the card. If you tap the card sharply so that it will fly off the jar, the coin will fall straight down into the jar. You can also do this with an egg and a jar of water. In this case the egg must be seated on a matchbox or other small box to keep it stable. When the card is tapped, the egg will fall down into the jar of water. The inertia of the coin to remain at rest causes it not to move with the card.

The students or teacher may then place the card on a table with the coin on top. Begin to move the card at a steady pace, the suddenly stop the card. The coin will continue to move due to its inertia to remain in motion.

Engage 2

Student Activity:

Set up lab stations of four students. Each station will need a small dump truck or cart filled with rocks, a rubber band, and a spring scale. The students should attach the spring scale to the rubber band and hook the other end of the rubber band to the dump truck or cart filled with rocks. Then they will slowly begin to pull the cart using the spring scale. Carefully observing the rubber band and spring scale, students should see that the greatest stretching and force on the scale occurs before the truck even moves. This is due to the inertia of the truck to remain at rest.

(Video- Exploring the Laws of Motion, 1993 United Learning, Inc., pg. 8)

Using a string strong enough to hold up a book, suspend a book from a hook (about 12 inches from the hook to the book). Tie another string around the book and let it hang down about 12 inches. Ask the students which string will break if you pull the one on the bottom. Then quickly jerk the bottom string straight down. The top string should break due to the inertia of the book to remain at rest.

ExploreExploration 1

Activity: Dare you to stop meClass Time: 30 minutesObjective: The learner will use equipment to measure time and distance so that the motion of the object can be determined.Materials

Air puckMeter stickStopwatch

Management Note: Activity should be conducted on a level surface such as a tennis or basketball court.

Air Puck: use the “Hover Puck ™” (Shaper Image Model #EC500) to simulate the motion of a flying saucer flying far from any gravitational field. Students will experiment with straight line motion at a constant speed. The point is to remove as many forces upon the object as possible. The puck floats on a layer of air and thus most friction is eliminated.

1. Have students observe the motion of the puck traveling at two different speeds. (Launched with different force magnitudes)

2. Have students measure off one meter, two meters and three meters and time the how long the puck takes to cover each meter. One student should puck the puck, one student should time as it crosses 1m, another students times as it crosses 2m and another times as it crosses 3m. This way, only one initial force is given. On a level surface students will find it takes the same length of time to go each of the meter distances.

3. Have students prepare motion maps of the motion. A Motion map: a drawing of the object showing where it is at different times; a “multiple exposures” drawing.

4. Have the students calculate the speed by dividing the distance the puck travels by the time it takes to travel that distance. s = d/t

5. Have the students plot the distance from the start versus elapsed time. Students may use a graphing calculator or spreadsheet program for creating a data chart and graph.

6. Have the students plot the speed versus time elapsed. Was the speed constant? Why or why not? What forces were acting on the puck? How does this compare to a ship in space?

Exploration 2

Activity Knocked off courseClass Time: 20 minutesObjective: The learner will explain the results of applying a force to an object.

MaterialsAir puckRubber malletDigital camera or video camera

Kicked Air Puck: using the “Hover Puck” and a rubber mallet (a hard rubber ball taped to a meter stick will suffice) discover the effects on the motion of an otherwise un-accelerated object with a force applied over a short time.

1. Set the puck in motion. Use a video camera or digital camera with video mode to capture the motion of the puck. If possible take the video shot from above the action.

2. After the puck has traveled a meter or so, use the mallet to tap the puck. Don’t push the puck, give it a quick bump.

3. Repeat this several times whacking the puck in different directions at 90°, 45°, 120° and 180°. Does the puck go in the exact direction of the force every time?

4. Now whack the puck at 90° but using small, medium, then large forces. Does the amount of force make a difference on the puck’s angle of motion?

5. Use the video to determine what affect the direction and size of the force had on the motion of the puck.

ExplainQuestion series: (Use some or all of the questions to guide student thoughts and help them construct knowledge. Insert questions as needed to keep this discussion going and reach a higher level of thinking)

1. How does an object behave when there are no forces acting upon it? It will stay in one spot or move at a constant speed in one direction.

2. When the puck was moving in activity one what force(s) were acting upon it? No forces were acting on it to keep it in motion. Gravity was a constant force that kept the puck on the ground but did not affect the straight line motion.

3. Why didn’t the puck move in a perfectly straight line? Inconsistencies in the floor or ground. Other answers could also be correct.

4. Why did the puck not move each equal distance in exactly the same time? Could be many reasons including: the reaction time of the persons with the stopwatches, the ground was not level, there was still some friction.

Summary: In a perfect situation, the puck would move forever in a straight line with exactly the same speed.

5. What is required to change the speed or direction of the puck? The application of a force on the puck.

6. Did the puck move in the direction of the applied force? Not necessarily. If the force were applied at 90o to the direction of motion of the puck, the puck would continue moving but at an angle somewhere between the original direction and

the direction of the force. A larger force causes the motion to be more in the direction of the force.

Review the pictures or video of the pucks motion. When no force was added, the puck traveled in a straight line with a constant speed. When the puck was in motion and struck at right angles, the puck traveled off at an angle to the original direction and at an angle to the direction of the force. Depending on the size of the force, the angle to the original direction changes.

Motion: when an object changes its position; when it moves.

Speed: the rate at which an object moves; how far something moves divided by the time it takes to make the move.

Direction of Motion: where the object is moving. Draw a straight line from where the object was to where it is now.

Motion map: a drawing of the object showing where it is at different times; a “multiple exposures” drawing.

Force: a push or pull.

Equilibrium: when all forces are balanced.

Balanced force: when all the forces are cancelled by other forces.Friction: the force that happens with two surfaces touch.Force diagram: a sketch that shows all the forces acting on an object.

ElaborateElaboration 1

Experiment Flag me downClass Time: 30 minutesObjective 1: The learner will identify size and direction of a force.

Objective 2: The learner will determine if motion is constant or accelerated.

Objective 3: The learner will explain the results of applying a force to an object.

Materials:Air puckPaper for a sailMasking tape

ScissorsMeter stickStopwatch

Activity Overview One usually thinks about applying a force to an object such as the puck. In the Elaboration 1 the force will be applied to move the air as the puck moves. A sail will push the air along with the motion of the puck and the air will push back thus slowing the puck to a gradual stop.

Preparation Cut different sizes of sails from the paper. Attach a sail to the air puck using tape. The sail may be wrapped around the circumference of the puck. Since the sail is moving an area of air, the area of the sail should be measured.

In order to make sense of the results, the force applied to the puck must be the same each time. Brainstorm with the class ways in which they can be sure the force is very close to the same each trial.

1. Measure the size of your small sail and record.

2. Place the puck at a marked spot and apply a force (blow into the sail for a count of 5).

3. Let the puck travel until it stops.

4. Measure the distance and time the puck traveled. What was the direction and motion?

5. Measure the size of the large sail and record.

6. Replace the small sail with the larger sail and place the puck at the starting line. Apply the same force as in the first trial (blow into the sail for a count of 5).

7. Take the distance and time measurements.

EvaluateStudents will journal what they learned about Newton’s first law of motion from the hover puck activities.

Dare You to Stop Me

Class Time: 30 minutesObjective: The learner will use equipment to measure time and distance so that the motion of the object can be determined.Materials

Air puckMeter stickStopwatch

Air Puck: use the “Hover Puck ™” (Shaper Image Model #EC500) to simulate the motion of a flying saucer flying far from any gravitational field. Students will experiment with straight line motion at a constant speed. The point is to remove as many forces upon the object as possible. The puck floats on a layer of air and thus most friction is eliminated.

1. Have students observe the motion of the puck traveling at two different speeds. (Launched with different force magnitudes)

2. Have students measure off one meter, two meters and three meters and time the how long the puck takes to cover each meter. One student should puck the puck, one student should time as it crosses 1m, another students times as it crosses 2m and another times as it crosses 3m. This way, only one initial force is given. On a level surface students will find it takes the same length of time to go each of the meter distances.

3. Have students prepare motion maps of the motion. A Motion map: a drawing of the object showing where it is at different times; a “multiple exposures” drawing.

4. Have the students calculate the speed by dividing the distance the puck travels by the time it takes to travel that distance. s = d/t

5. Have the students plot the distance from the start versus elapsed time. Students may use a graphing calculator or spreadsheet program for creating a data chart and graph.

6. Have the students plot the speed versus time elapsed. Was the speed constant? Why or why not? What forces were acting on the puck? How does this compare to a ship in space?

DARE YOU TO STOP ME CLASS DATA TABLE

Speed at . . . (m/s)

Group # 1m 2m 3m

1

2

3

4

5

6

7

8

Class Average

1. How does an object behave when there are no forces acting upon it?

2. When the puck was moving in activity one what force(s) were acting upon it?

3. Why didn’t the puck move in a perfectly straight line?

4. Why did the puck not move each equal distance in exactly the same time?

5. Graph distance on y-axis, time on x-axis = speed

6. Graph speed on y-axis, time on x-axis = acceleration

Knocked off Course

Class Time: 20 minutesObjective: The learner will explain the results of applying a force to an object.Materials:

Air puckRubber malletDigital camera or video camera

Kicked Air Puck: using the “Hover Puck” and a rubber mallet (a hard rubber ball taped to a meter stick will suffice) discover the effects on the motion of an otherwise un-accelerated object with a force applied over a short time.

1. Set the puck in motion. Use a video camera or digital camera with video mode to capture the motion of the puck. If possible take the video shot from above the action.

2. After the puck has traveled a meter or so, use the mallet to tap the puck. Don’t push the puck, give it a quick bump.

3. Repeat this several times whacking the puck in different directions at 90°, 45°, 120° and 180°. Does the puck go in the exact direction of the force every time?

4. Now whack to puck at 90° but using small, medium, then large forces. Does the amount of force make a difference on the puck’s angle of motion?

5. Use the video to determine what affect the direction and size of the force had on the motion of the puck.

Force Angle Observations

45°

90°

120°

180°

1. What is required to change the speed or direction of the puck?

2. Did the puck move in the direction of the applied force?

Flag Me Down

Class Time: 30 minutesObjective 1: The learner will identify size and direction of a force.Objective 2: The learner will determine if motion is constant or accelerated.Objective 3: The learner will explain the results of applying a force to an object.Materials:

Air puckPaper for a sailMasking tapeScissorsMeter stickStopwatch

Activity Overview One usually thinks about applying a force to an object such as the puck. In the Elaboration 1 the force will be applied to move the air as the puck moves. A sail will push the air along with the motion of the puck and the air will push back thus slowing the puck to a gradual stop.

Preparation Cut different sizes of sails from the paper. Attach a sail to the air puck using tape. The sail may be wrapped around the circumference of the puck. Since the sail is moving an area of air, the area of the sail should be measured.

1. In order to make sense of the results, the force applied to the puck must be the same each time. Brainstorm with the class ways in which the can be sure the force is very close to the same each trial.

2. Measure the size of your small sail and record.

3. Place the puck at a marked spot and apply a force (blow into the sail for a count of 5).

4. Let the puck travel until it stops.

5. Measure the distance and time the puck traveled. What was the direction and motion?

6. Measure the size of the large sail and record.

7. Replace the small sail with the larger sail and place the puck at the starting line. Apply the same force as in the first trial (blow into the sail for a count of 5).

8. Take the distance and time measurements.

Size of Sail Distance (m) Time (sec) Speed (s=d/t)

Small

___cm X ___cm

Large

___cm X ___cm

1. Calculate the speed of the puck with the small sail and large sail using the formula speed = distance / time. Record in table.

2. Add your calculated speeds to the class data table.

3. Which sail increased the speed of your puck? Why?

4. Which sail decreased the speed of your puck? Why?