Forces The Nature of Force Friction and Gravity Newton’s First and Second Laws Newton’s Third Law Rockets and Satellites Table of Contents

Forces

The Nature of Force

Friction and Gravity

Newton’s First and Second Laws

Newton’s Third Law

Rockets and Satellites

Table of Contents

Forces

Learning Objectives

1. Describe what a force is.

2. Describe how balanced and unbalanced forces are related to an object’s motion.

Forces

What is a Force? (No lab write-up)Goal: Determine more than one way to create a force reading using the force sensor.

Results: What were the ways you used to create a force? How did or would you create a weak force? A stronger force? Can forces be negative? How did you get a negative force?

Conclusions: Based upon these ways, what is a force? Does a force depend on direction? How do you know from the experiment? How else is a force described outside of direction?

Forces - The Nature of Force

Combining Forces (Real World Examples + Tug-of-War Challenge)

Do forces usually act alone? The combination of all forces acting on an object is called the net force.


Unbalanced Forces

Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion.


Balanced Forces

Balanced forces acting on an object do not change the object’s motion.

Forces

A force is…

A. Always balanced.

B. A push or a pull in a particular direction.

C. A pull that pushes.

D. What Jedi Knights possess.

Forces

A force is measured by its

A. Power only.

B. Strength or magnitude only.

C. Strength or magnitude and direction.

D. Direction and its pull.

Forces

A sky diver experiences a 900 N downward force and a 200 N upward force. What is the net force (in

the correct direction)?A. 700 N up

B. 700 N down

C. 1100 N up

D. 1100 N down

Forces

Which direction will the cart below move?

A. The cart will not because the forces are balanced.

B. Left because the net force is -90 N to the left.

C. Right because the net force is 90 N to the right.

D. Up because the cart is being pulled to the left and to the right.

Forces

The two dogs in the picture below are pulling on a rope. The dog on the left is pulling at 200 N while

the dog on the right is pulling at 200 N. What direction will the rope move?

A. South because the forces are balanced.

B. West because the dog on the left is pulling harder.

C. East because the dog on the right is stronger.

D. The rope will not move because the forces are balanced.

Forces

Asking QuestionsBefore you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions.

What is a force? A force is a push or pull.

What happens when forces combine?

Forces combine to produce a net force.

Question Answer

- The Nature of Force

Forces

Links on Force

Click the SciLinks button for links on force.

- The Nature of Force

Forces

End of Section:The Nature of

Force

Forces

Noggin Knockers/Homework- p. 39: 1b, 1c, 2b, 2c (8 points total- 2 points each)

1 (1 point per part for 2 pts. total)- (A) Balanced forces do not affect an object’s motion because they cancel out. (B) Unbalanced forces will cause the object to move or change it’s motion.

2 (2 points)- Arrow (B) because it is longer.

3 (2 points)- 120 N + 150 N = 270 N downward (strength & direction)

4 (2 points)- 200 N – 100 N = 100 N to the right

Forces

Learning Objective

1. Describe friction and identify the factors that determine the frictional force between 2 objects.

Forces

Friction ExperimentsGoal: Determine what 2 factors affect the frictional force between two objects. Also, determine how friction can be reduced.

Hypothesis (x3): For Part 1, determine which surface (floor or rug) will produce the greatest frictional force. For Part 2, determine how the added weight will affect the frictional force. For Part 3, determine how adding wheels will affect the frictional force (w/o weights).

Procedure (Use the Digits function, not the Graph function): Part 1- Push an upside-down go-car (wheels up) across the floor using the force sensor to determine the frictional force that needs to be OVERCOME so the car can move at a constant speed. Make sure you ZERO the sensor before you start pushing. Repeat the procedure above with the rug.Part 2- Add weight to the go cars and repeat Part 1. Part 3- After removing the weights, flip the go-car over so that the wheels are on the floor and repeat Part 1.

Results: Organize your results for each part of the procedure.

Forces

Friction ExperimentConclusions (in complete sentences): 1. Which surface produced a greater frictional force? Explain why this is

the case.

2. What was the effect of extra weight on the frictional force? What was the effect of wheels on the frictional force?

3. Make your claim/conclusion (make sure it relates to the goal below), and back it up with evidence from the experiment. Use your conclusions from #1 and #2 above for guidance.

Goal: Determine what 2 factors affect the frictional force between two objects. Also, determine how friction can be reduced.

Forces

Friction Notes

For friction notes, examine your conclusions from the Friction Experiment.

Friction is a force that resists or inhibits the motion of objects when they move against each other.

Also, you should know that the type of surface of an object and that how hard surfaces push together affect friction (you increased the 2nd variable in bold by adding more weight).

Lastly, know how wheels affect friction as well as any other ways to reduce friction.

Forces

Markie and Suzy are moving a safe across the floor. Which of the following describes the frictional

force?

A. Markie and Suzy both push the safe the same direction.

B. The weight of the safe exerts a downward force.

C. The floor pushes upward on the safe.

D. There is some resistance going against the direction the safe is moving.

Forces

Which change would require more force to pull the wooden block up the ramp?

A. Glue sandpaper to the surface of the ramp.

B. Reduce the mass of the wooden block.

C. Restack the books so the thinnest book is on the bottom.

D. Have the student use two hands.

Forces

Which of the following would produce the greatest frictional force between 2 objects?

A. A 100 kg wooden block sliding across a smooth table.

B. A 200 kg wooden block sliding across a smooth table.

C. A 100 kg wooden block sliding across a rug.

D. A 200 kg wooden block sliding across a rug.

Forces

The diagrams below show a person moving a 50-kilogram

object up a ramp. In which diagram is there the least

amount of friction on the object?

A. Diagram 1

B. Diagram 2

C. Diagram 3

D. Diagram 4

Forces

The wheels and gears of machines are greased in order to decrease

A. Potential energy.

B. Output.

C. Efficiency.

D. Friction.

Forces

Learning Objectives

1. Identify the factors that affect the gravitational force between two objects, and describe how they affect this force.

2. Explain why objects accelerate during free fall (by describing how gravity affects falling objects).

Forces

Gravitational Pull Experiment- Part 1 (write conclusions in your notes)

Goal- Determine what affects the gravitational force or attraction between 2 objects by using magnets & Planet Data.

Background: This brief experiment is only a MODEL of the gravitational pull between 2 objects.

Results: Determine what happens to the force of attraction between the magnets as they get closer together.

Conclusion: What affects the gravitational pull between 2 objects?

Forces - Friction and Gravity

GravityThe force of gravity on a person or object at the surface of a planet is known as weight.

Right now you are experiencing 1G, which is the amount of force due to the gravity on Earth.

When you ride on a rollercoaster, you will experience more than 1G. Sometimes, you are feeling 3, 4, or 5 G’s due to the acceleration of the rollercoaster.

Forces

Gravitational Pull Experiment- Part 2:Mass & Gravitational Pull of the Planets

Name Mass (X 1024 kg) Gravitational force on the surface (relative to Earth)

Pluto 0.0013 0.1

Moon 0.07 0.2

Mars 0.64 0.4

Earth 5.98 1.0

Jupiter 1900 2.4

Sun 1,989,000 7.1

Conclusion: So, what else affects the gravitational pull between 2 objects?


Gravity

Two factors affect the gravitational attraction between objects: mass and distance.

Forces

Which two factors determine the gravitational attraction between two objects?

A. time and temperature B. shape and orbital speedC. color and hardnessD. mass and distance apart

Forces

The gravitational force between the Moon and Earth depends on

A. Their masses only.

B. Their diameters only.

C. Their masses and how far apart they are.

D. Their diameters and how far apart they are.

Forces

Suppose three new planetary bodies are discovered near Earth. They all have the same mass. Planet A is 9 million miles away, Planet B is 7 million miles

away, and Planet C is 30 million miles away. Which planet would Earth have the greatest gravitational

attraction for? A. Planet A

B. Planet B

C. Planet C

D. Planet D

Forces

On which planet in our solar system would you feel the most gravitational pull?

A. Earth

B. Saturn

C. Jupiter

D. Mars


Earth 5.98 1.0 Mars 0.64 0.4 Jupiter 1900 2.4 Pluto 0.0013 0.1 Moon 0.07 0.2 Sun 1,989,000 7.1

Forces

Why does the Sun have the greatest gravitational pull?

A. It has the lowest mass.

B. It has the most mass.

C. It’s the closest to the Earth.

D. It’s gravitational force is 7.1 times that of Earth.


Earth 5.98 1.0 Mars 0.64 0.4 Jupiter 1900 2.4 Pluto 0.0013 0.1 Moon 0.07 0.2 Sun 1,989,000 7.1

Forces

Suppose a new planet was discovered that had a mass of 4.00 (x 1024 kg). What would be a possible

gravitational force for this new planet? A. 0.85

B. 0.3

C. 1.4

D. 8.0


Pluto 0.0013 0.1 Moon 0.07 0.2Mars 0.64 0.4 Earth 5.98 1.0 Jupiter 1900 2.4Sun 1,989,000 7.1

Forces

Motion TestMotion Test: Commonly Missed Problems

Forces

Sneaker Traction Friction Experiment (Just record your group’s data)

Goal: Determine which sneakers have the best traction (by examining the frictional force).

Background: What will you be measuring that indicates good traction?

Procedure: Same as Part 1 from the previous Friction Experiment (minus the rug). Record the frictional force on the SMART Board for the group member who had the shoes with the most traction.

Results: Organize your results into a table for your group. Add the other groups’ data into your table.

Conclusion: Make your claim (related to the goal) & back it up with evidence and relate it to what affects the frictional force between 2 objects from the previous experiment.

Forces

Learning Objectives

1. Explain why objects accelerate during free fall (by describing how gravity affects falling objects).

Forces

Acceleration Due to Gravity (No lab write-up)Goal: Determine the acceleration due to gravity for objects in free fall.

Pre-Lab Demos (Dropping Paper and a Ball): Determine if objects of different masses accelerate slower or faster by observing when they hit the ground. Does the mass of an object change how fast it free falls? Why or why not? So, does the force due to gravity affect all objects on Earth the same?

Hypothesis: We will do the hypothesis as a class verbally.

Procedure: 1. Use a motion sensor from a high height (on the Digits and Acceleration settings)

& drop a ball (AFTER HITTING PLAY) to determine the Acc. due to Gravity. 2. Repeat 3-5 times and RECORD the acceleration right before the ball hits the

ground (hit play to pause the data collection).

Results/Conclusions (Make sure you can answer these questions):1. What is the acceleration due to gravity from the experiment? 2. The actual value is m/s/s. How close were you to the actual value? 3. What may cause the ball to not accelerate as quickly (what could slow it down)?

Forces

Free Fall = When gravity is the only force acting on the object

Use the graph to answer the following questions.

- Friction and Gravity

Forces

Free Fall

The slope is 9.8. The speed increases by 9.8 m/s each second. This is the actual acceleration due to gravity on Earth without any air resistance.

Calculating:

Calculate the slope of the graph. What does the slope tell you about the object’s motion?


Forces

Free Fall

58.8 m/s

Predicting:

What will the speed of the object be at 6 seconds?


Forces

Free Fall

The speed values would not change.

Drawing Conclusions:

Suppose another object of the same size but with a greater mass was dropped instead. How would the speed values change?



Air Resistance

Falling objects with a greater surface area experience more air resistance.

Forces

Two objects are dropped from the top of a tall building and there is no wind. One object is a 16 lb. bowling ball and the other is a basketball. What will

be each object’s approximate acceleration when they are dropped?

A. 9.8 m/s/s for the basketball and 8.0 m/s/s for the bowling ball.

B. 0.0 m/s/s for both objects.

C. 9.8 m/s/s for both objects.

D. 9.8 m/s/s for the bowling ball and 4.9 m/s/s for the basketball

Forces

When gravity is the only force acting on an object, then that object is

A. Moving at a constant velocity.

B. Not accelerating.

C. In free fall.

D. Moving quickly.

Forces

Suppose a large rock is dropped straight down from a high cliff while the other is pushed out from the

top of the cliff. Which one will land first and WHY?

A. The rock that is pushed out from the cliff will hit first because it had an extra force to make it fall faster.

B. The rock that’s dropped straight down will hit first because it has a shorter path to travel.

C. They will both hit the ground at the same time because gravity acts the same on all free-falling objects.

D. Neither will hit the ground.

Forces

Why will a leaf fall slowly to the ground while other objects fall quickly?

A. It’s lighter.

B. Air resistance

C. Gravity

D. They just do.

Forces

Air resistance is a type of

A. band.

B. gravity.

C. friction.

D. Law.

Forces

Friction Gravity

Comparing and ContrastingAs you read, compare and contrast friction and gravity by completing a table like the one below.

Effect on motion Opposes motionPulls objects toward one another

Depends onTypes of surfaces involved, how hard the surfaces push together

Mass and distance

Measured in Newtons Newtons


Forces

Links on Friction

Click the SciLinks button for links on friction.


Forces

Free Fall

Click the Video button to watch a movie about free fall.


Forces

End of Section:Friction and

Gravity

Forces

Noggin Knockers/Hwk.- p. 50: 1b, 2b, 2c, 3a, 3b, 3c (10 pts.)

1 (a)- Push = Arrow A (1 pt.)

(b) Friction = Arrow C (1 pt.)

(c) Gravity = Arrow D (1 pt.)

(d) 300 N to the left. (2 points- 1 pt. for value, 1 pt. for direction)

2 (a) More mass = Greater Grav. Attraction (1 point)

(b) Closer together/less distance = Greater Grav. Attraction (1 point)

3 (1 point)- An object’s mass does not affect its acceleration during free fall.

4a (1 point)- Force that changes = air resistance/friction

4b (1 point)- Force that stays constant = gravity

Forces

Learning Objectives1. Apply Newton’s 1st Law of Motion to real world

examples.• Key Term: Inertia

2. Apply Newton’s 2nd Law of Motion to real world examples.• Key Terms: Force, Mass, Acceleration

Forces

Introduction to Newton’s 1st Law

What happens to your body when a car or rollercoaster first takes off quickly?

What happens to your body when a car or rollercoaster stops abruptly?

Forces

Newton’s 1st Law of MotionObjects in Motion (Pencil on a cart being stopped): Stay in motion until a force stops them from moving.

Objects at Rest (Tablecloth Demo): Stay at rest until an outside force causes the object to move.

Inertia: The tendency of an object to stay in motion or stay at rest. What does inertia depend on? Example- Which has more inertia a toy car or a large truck?

As mass increases, inertia increases.

Newton’s 1st Law:An object in motion will stay in motion unless acted on by an unbalanced force. Also, an object at rest will remain at rest unless acted on by an unbalanced force.

Forces

Why is it difficult to stop a large fast-moving football player?

A. He has a small inertia.

B. An object at rest will stay at rest until an unbalanced force causes it to move.

C. An object in motion will stay in motion until an unbalanced force acts on it.

D. Because he plays for Notre Dame.

Forces

Why is it difficult to move heavy objects from rest?

A. Because they are at rest.B. An object at rest tends to remain at rest until an

unbalanced force acts on it.C. An object in motion will remain in motion until an

unbalanced force acts on it.D. Because it’s light in weight.

Forces

The tendency of an object to remain at rest or remain in motion is called ___________

A. Mass.

B. Inertia.

C. Newton’s 1st Law.

D. Density.

Forces

Which of the following affects the amount of inertia an object possesses?

A. Mass

B. Volume

C. Gravity

D. Friction

Forces

Which of the following has the most inertia?

A. A table

B. Grandma

C. A Toyota Yaris

D. A freight train

Forces

What Affects Force? (Newton’s 2nd Law)

1. Suppose you push two people who have the same mass. You push with more force on one person vs. the other. Which person would accelerate faster from rest?

2. Suppose you push two people and they both accelerate at the same rate. However, one person has much more mass than the other. Which one required more force to accelerate?

3. Suppose you push two people with the same amount of force. However, one person has more mass than the other. Which person would accelerate at a faster rate?

Forces

Newton’s 2nd Law ExperimentGoal: Determine the relationship between Force, mass, and acceleration for an

object (a Go-car in this case).

Hypothesis (x 3): 1. What has to happen to the force required to move an object if acceleration

increases (& mass is constant)? 2. What would happen to the force if mass increases (& acceleration is constant)? 3. What would happen to the acceleration if mass increases (& the force is

constant)?

Procedure (use Digits): Part 1- Keeping mass on the cart constant, determine the relationship between force

and acceleration. (Determine the force needed to accelerate the car slowly and compare to the force needed to accelerate the car quickly)

Part 2- Keeping acceleration constant, determine the relationship between mass and force. (Determine the force needed to move the car from rest to a constant speed with weights and compare to force required without weights at a constant speed). This can be tricky to achieve so as long as the acc. Is close it’s okay.

Part 3- Keeping force constant, determine the relationship between mass and acceleration. (Determine the acceleration with and without weights but keep the force the same)

Results: Organize your results in a table for EACH part.

Forces

Newton’s 2nd Law ExperimentConclusions (Using your data…) 1. What was the relationship for each part? For example, as

acceleration increased, the force (increased or decreased). Use data from the experiment back up your claims.

a) Force and acceleration (constant mass)- from Part 1 Datab) Force and mass (constant acceleration)- from Part 2 Datac) Mass and acceleration (constant force)- from Part 3 Data

2. Which of the equations below represents the relationships you discovered? Choose 2- one from (a) or (b) and one from (c) or (d). [F is force, m is mass, and a is acceleration]

a) F = m/ab) F =m x ac) a = F x md) a = F/m

Forces

F = m x aAcceleration due to gravity & Constant force

Force, mass, and acceleration units:

1 N = 1 kg x m/s/s

Acc. Due to Gravity

=a =

Forces

Calculating Force

A speedboat pulls a 55-kg water-skier. The force causes the skier to accelerate at 2.0 m/s2. Calculate the net force that causes this acceleration.

Read and Understand

What information have you been given?

Mass of the water-skier (m) = 55 kg

Acceleration of the water-skier (a) = 2.0 m/s2

- Newton’s First and Second Laws

Forces

Calculating Force


Plan and Solve

What quantity are you trying to calculate?

The net force (Fnet) = __

What formula contains the given quantities and the unknown quantity?

a = Fnet/m or Fnet = m X a

Perform the calculation.

Fnet = m X a = 55 kg X 2.0 m/s2

F = 110 kg • m/s2

F = 110 N


Forces

Calculating Force


Look Back and Check

Does your answer make sense?

A net force of 110 N is required to accelerate the water-skier. This may not seem like enough force, but it does not include the force of the speedboat's pull that overcomes friction.


Forces

Calculating Force

Practice Problem

What is the net force on a 1,000-kg object accelerating at 3 m/s2?

3,000 N (1,000 kg X 3 m/s2)


Forces

Calculating Acceleration

Practice Problem

What is the acceleration of an object in free fall with a weight of 98 N and a mass of 10 kg? Does your answer make sense? Note that weight is the force due to gravity!

a = F/m

a = 98 N/10 kg = 9.8 m/s2


Forces


Practice Problem

What is the acceleration of a 100 kg couch being pulled across the floor with a force of 200 N?

a = F/m

a = 200 N/100 kg = 2 m/s2


Forces

Noggin Knockers

Forces


Practice Problem

Determine the amount of force required to accelerate a 1000 kg roller coaster at 5 m/s/s?

F = m x a

F = 1000 kg x 5 m/s/s = 5000 N or 5000 kg x m/s/s


Forces


Practice Problem

Determine the weight of 50 kg person. Hint- You should already know the acceleration since weight is the force of gravity acting on your body.

F = m x a

F = 50 kg x 9.8 m/s/s = 490 N


Forces


Practice Problem

What is the acceleration of a 2 kg ball thrown with a force of 20 N?

a = F/m

a = 20 N/2 kg = 10 m/s2


Forces

Which of the following best describes the relationships between force, mass, and

acceleration?

A. As mass decreases, the net force will increase if the acceleration remains constant.

B. As mass and acceleration increase together, so will the net force.

C. As mass increases so will the acceleration, but force will remain constant.

D. As acceleration increases and the mass remains constant, the net force will decrease.

Forces

Suppose you are pushing a car with a certain amount of force. What will happen to the car’s acceleration if the mass of the car increases?

Assume the amount of applied force remains the same.

A. The acceleration will increase.

B. The acceleration will decrease.

C. The acceleration will remain the same.

D. There is not enough information from the problem.

Forces

Suppose a small car strikes a wall. Which of the following would exert the same amount of force as

the car?

A. A truck that’s twice as heavy and has twice the acceleration of the car.

B. A truck that’s half as heavy with the same acceleration of the car.

C. A truck that’s the same mass with half of the acceleration of the car.

D. A truck that’s twice as heavy with half of the acceleration of the car.

Forces

How much force does a 100 kg Notre Dame football player exert when he accelerates at 5 m/s/s into a

Nittany Lion?A. 500 N

B. 20 N

C. 100 N

D. 5 N

Forces

Determine the amount of forceforce exerted on a 10 kg dumbbell in free-fall.

A. 9.8 N

B. 10 N

C. 98 N

D. It cannot be determined.

Forces

A force of 500 N is exerted on a 100 kg safe. What is the safe’s acceleration?

A. 0.2 m/s/s

B. 50,000 m/s/s

C. 9.8 m/s/s

D. 5 m/s/s

Forces

OutliningAs you read, make an outline about Newton’s first and second laws. Use the red headings for the main topics and the blue headings for the subtopics.

Newton’s First and Second Laws

I. Newton’s First Law of MotionA. InertiaB. Inertia Depends on Mass

II. The Second Law of MotionA. Changes in Force and Mass


Forces

More on Newton’s Laws

Click the PHSchool.com button for an activity

about Newton’s laws.


Forces

End of Section:Newton’s First

and Second Laws

Forces

Noggin Knocker Calculations

Forces

Homework: p. 54 (1a, 1c, 2 all, and 3)

1a- An object will remain at rest or remain in motion until acted on by an unbalanced force.

1c- Your body wants to remain at rest.

2a- Examples: A force is required to get an object to accelerate, the force an object exerts is equal to its mass multiplied its acceleration, etc.

2b- Double the mass.

2c- Greater mass means more force is required to get the car to accelerate.

3- F = m x a = 800 kg x 5 m/s/s = 4000 N

Forces

Noggin Knocker Calculations

Forces

Noggin Knockers/Hwk. (8 pts.- 2 pts each)

1- Your body wants to remain at rest.

2- Double the mass.

3- Greater mass means more force is required to get the car to accelerate.

4- F = m x a = 800 kg x 5 m/s/s = 4000 N

Forces

Learning Objectives

1. Apply Newton’s 3rd Law of Motion to real world examples.

Forces

Newton’s 3rd LawBalloon Race Activity: Determine what makes the balloon propel across the room based upon the forces involved.

Newton’s 3rd Law:For every action, there is an equal and opposite reaction.

What are the action-reaction forces for the following:

–Rocket taking off?–Punching a wall?–Jumping from a high height to the ground?– Hammering a nail?

Forces

Forces on an object moving to the left

Push or Pull

Gravity

Friction

Reaction Force/Floor or air pushing up

Forces

Which of the following is an example of Newton’s 3rd Law of Motion?

A. When you do push-ups, you won’t stop until an unbalanced force causes you to stop.

B. The net force you exert when doing a push-up is equal to your body mass multiplied by the acceleration due to gravity.

C. When you do a push-up, an equal and opposite force pushes back on your body or hands.

D. What’s a push-up?

Forces

What direction will the contraption shown below go when the string is burned?

A. left

B. right

C. up

D. down

Forces

Why will the contraption below move to the right?

A. Friction is going to the left

B. The rubber band snaps to the left, so the equal and opposite reaction is for the wooden platform to move to the right.

C. Gravity pulls the wooden platform to the right when the rubber band snaps.

D. The pencils cause the wooden platform to move to the right because friction acts in the opposite direction.

Forces

If you add mass to the wooden platform, what effect would that have on the distance it travels?

A. The distance would increase.

B. The distance would decrease.

C. The distance would not change.

D. It would travel the same distance in the opposite direction.

Forces

Learning Objectives

1. Explain how an object’s momentum is conserved & be able to calculate momentum.

2. State the law of conservation of momentum.

Forces

Conservation of MomentumMomentum- Use what you think momentum is and modify your definition based upon what is discussed in class (if needed).

Newton’s Cradle: Is the total momentum lost or transferred for this activity? How do you know?

Bouncing Sports Balls: What makes the sports balls on top bounce as high as they do?

Colliding Cars with Tape: Is the total momentum lost or transferred for this activity? How do you know? Be sure to think about how the direction of the cars affect this experiment.

Forces -

Conservation of MomentumLaw of the Conservation of Momentum (mass in motion): The total momentum is conserved (or does not change) for any group of objects, unless outside forces (such as friction) act on the objects.

- Newton’s Third Law

Forces

Relationship between Momentum, Mass, & Velocity

What causes an object’s momentum to increase?

How does velocity affect momentum?

How does mass affect momentum?

Momentum = m x v

Forces

Calculating Momentum

Which has more momentum: a 3.0-kg sledgehammer swung at 1.5 m/s or a 4.0-kg sledgehammer swung at 1.0 m/s?

Read and Understand

What information have you been given?

Mass of smaller sledgehammer = 3.0 kg

Velocity of smaller sledgehammer = 1.5 m/s

Mass of larger sledgehammer = 4.0 kg

Velocity of larger sledgehammer = 1.0 m/s


Forces



Plan and Solve

What quantities are you trying to calculate?

The momentum of each sledgehammer = __

What formula contains the given quantities and the unknown quantity?

Momentum = Mass X Velocity

Perform the calculation.

Smaller sledgehammer = 3.0 kg X 1.5 m/s = 4.5 kg x m/s

Larger sledgehammer = 4.0 kg X 1.0 m/s = 4.0 kg x m/s


Forces



Look Back and Check

Does your answer make sense?

The 3.0-kg hammer has more momentum than the 4.0-kg one. This answer makes sense because the 3.0-kg hammer is swung at a greater velocity.


Forces

The total momentum before and after a collision (in the absence of friction) is always

A. Constipated.

B. Conserved.

C. Different.

D. Reserved.

Forces

Suppose the total momentum before 2 cars collide is 200 kg x m/s. What is total momentum after the

collision (in the absence of friction)? A. 100 kg x m/s

B. 0 kg x m/s

C. 200 kg x m/s

D. There is not enough information in the question.

Forces

Which of the following would have the most momentum: a 1000 kg car moving at 10 m/s or a

1000 kg car moving at 20 m/s?

A. The car moving at 10 m/s.

B. The car moving at 20 m/s.

C. They have the same momentum.

D. The momentum cannot be determined.

Forces

Which of the following has the most momentum: bowling ball moving at 5 m/s or a tennis ball moving

at 5 m/s?A. The tennis ball.

B. The bowling ball.

C. They have the same momentum.

D. I was not paying attention.

Forces

What outside force causes momentum to not be “conserved” for almost every collision?

A. Gravity

B. Friction

C. Normal

D. Weight

Forces

Which has more momentum: a 1000 kg car moving at 20 m/s or a 2000 kg truck moving at 10 m/s?

A. The car

B. The truck

C. They both have the same momentum.

D. Football players from Notre Dame.

Forces

Forces Practice Test 1- Person shoving their friend

2- Unbalanced forces CHANGE an object’s motion.

3 & 4- Friction

5- 150 N to the right (200 N – 50 N = 150 N)

6- 50 N = Frictional Force; 300 N down = Gravitational Force; 300 N up = Reaction force (from the action of gravity pulling downward)

7- Shoes with lots of tread, sandpaper used in shop class, etc.

8- Air Resistance would change; Gravity would remain the same

9- Increase mass- Greater Grav. Pull; Lower distance- Greater Grav. Pull

10- Any number from 1.1 to 2.3 (between Earth and Jupiter’s Grav. pull)

11- Heavy objects- High Inertia and like to stay at rest more than lighter ones & are more difficult to stop moving. Seatbelts prevent your body from moving too far forward (wanting to stay in motion) when brakes are used

Forces

Forces Practice Test12- ½ the acceleration = ½ the force, so ½ of 20 N = 10 N

13- F = m x a = 50 kg x 2 m/s/s = 100 N

14- 9.8 m/s/s

15- 5 kg because it is lighter

16- Action- Striking the board; Reaction- Board pushes back onto your hand.

17- Increase the object’s velocity and mass

18- Momentum is the same before and after (w/o friction).

19- Friction

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Noggin Knockers/Hwk. (10 points- 2 pts. each)

1- You move backwards (or away).

2- Action force = you pushing the other person; Reaction force = the other person’s body pushes back onto you.

3- 0 kg x m/s

4- 0.06 kg x m/s

5- Dolphin because it is moving faster. Momentum of dolphin = m x v = 250 kg x 4 m/s = 1000 kg x m/s1000 kg x m/s

Momentum of manatee = 350 kg x 2 m/s = 700 kg x m/s700 kg x m/s

Forces

Noggin Knockers & Hwk: p. 61- 1a, 1b, 1c, 2a, 2c, 3a, 3b, & 5

1a- For every action there is an equal and opposite reaction.

1b- The reaction force is EQUAL and OPPOSITE to the action force.

1c- You would move the direction the ball is moving.

2a- Momentum is the mass x velocity of an object; 2b- The momentum of a parked car is 0 kg x m/s.

2c- Greater speeds means a greater momentum, which makes it more difficult to stop.

3a- The total momentum is the same before and after a collision (w/o friction).

3b- 0.06 kg x m/s

5- Momentum of dolphin = m x v = 250 kg x 4 m/s = 1000 kg x m/sMomentum of manatee = 350 kg x 2 m/s = 700 kg x m/s

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Momentum Activity

Click the Active Art button to open a browser window and access Active Art about momentum.


Forces


Practice Problem

A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has the greater momentum?

Golf ball: 0.045 kg X 16 m/s = 0.72 kg•m/s

Baseball: 0.14 kg X 7 m/s = 0.98 kg•m/s

The baseball has greater momentum.


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Practice Problem

What is the momentum of a bird with a mass of 0.018 kg flying at 15 m/s?

0.27 kg•m/s (0.018 kg X 15 m/s = 0.27 kg•m/s)


Forces

Previewing VisualsBefore you read, preview Figure 18. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions.

Conservation of Momentum

Q. What happens when two moving objects collide?

A. In the absence of friction, the total momentum is the same before and after the collision.

Q. What is the momentum of an object?

A. Its mass multiplied by its velocity


Forces

End of Section:Newton’s Third

Law

Forces - Rockets and Satellites

What Is a Satellite?

A projectile follows a curved path because the horizontal and vertical motions combine.



The faster a projectile is thrown, the father it travels before it hits the ground. A projectile with enough velocity moves in a circular orbit.



Depending on their uses, artificial satellites orbit at different heights.

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Main Idea

Detail Detail Detail

Identifying Main IdeasAs you read the section “What Is a Satellite?” write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea.

A satellite stays in orbit due to…

its inertia Earth’s gravity Earth’s shape

- Rockets and Satellites

Forces

End of Section:Rockets and

Satellites

Forces

Graphic Organizer

Friction between an unmoving book and desk

Type of Friction

Static

Occurs When Example

Sliding

Rolling

Fluid

An object is not moving

Two solid surfaces slide over each other

Rubber pads on a bicycle’s brakes

An object rolls across a surface

Ball bearings in skateboard wheels

A solid object moves through a fluid Air resistance

Forces

End of Section:Graphic Organizer

Documents

Forces The Nature of Force Friction and Gravity Newton’s First and Second Laws Newton’s Third Law Rockets and Satellites Table of Contents