Newton’s Laws of Motion Nancy S. Chu & Elizabeth Watson EDT 610: Instructional Design – Theory & Model Dr. Gladys Arome St. Thomas University June 24,

Newton’s Laws of Motion

Nancy S. Chu & Elizabeth Watson

EDT 610: Instructional Design – Theory & ModelDr. Gladys Arome

St. Thomas UniversityJune 24, 2009

Johnny the Inquirer

Johnny was on his way back home after school as usual, when he started pondering about why his body leaned forward whenever mom put on the brakes, and then it would get pressed on the seat when she stepped on the gas, if he was not even trying to move.

Strangely enough, it would happen every single day of his life…

Johnny the Inquirer

Suddenly, it hit him!

He remembered his teacher talking about Newton’s Laws of Motion.

While most people know what Newton's laws say, many people do not know what they mean (or simply do not believe what they mean).

Newton’s Laws of Newton’s Laws of MotionMotion

o First LawFirst Law – An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force.

o Second LawSecond Law – Force equals mass times acceleration.

o Third LawThird Law – For every action there is an equal and opposite reaction.

Newton’s First Law of Motion

Newton’s First Law of Motion, also known as Law of Inertia, states that an object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity unless it is acted upon by an unbalanced force.

First Law of MotionInertia is the

tendency of an object to resist changes in its velocity: whether in motion or motionless. These pumpkins will not move

unless acted on by an unbalanced force.

First Law of MotionOnce airborne,

unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!

First Law of Motion

Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

Newton’s First Law & You

Don’t let this be you. Wear seat belts.

Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.

Newton’s Second Law of Motion

According to Newton’s Second Law of Motion, acceleration depends on the object’s mass and on the net force acting on the object.

Mass

NetForceonAccelerati

The net force of an object is equal to the product of its mass and acceleration.


When mass is in kilograms and acceleration is in m/s2, the unit of force is in Newtons (N).

One Newton is equal to the force required to accelerate one kilogram of mass at one meter/second square.


Newton’s 2nd Law proves that different masses accelerate to the earth at the same rate, but with different forces.

We know that objects with different masses accelerate to the ground at the same rate.

However, because of the 2nd Law we know that they don’t hit the ground with the same force. F = maF = ma

98 N = 10 kg x 9.8 m/s98 N = 10 kg x 9.8 m/s22

F = maF = ma

9.8 N = 1 kg x 9.8 m/s9.8 N = 1 kg x 9.8 m/s22

Newton’s Third Law of Motion states that if one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object.

Newton’s Third Law of Motion


In other words: For every action, there is an equal and opposite reaction.


According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.

There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces.


Newton’s Third Law in Nature Consider the propulsion of

a fish through the water. A fish uses its fins to push water backwards. In turn, the water reacts by pushing the fish forwards, propelling the fish through the water.

The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards).

Flying gracefully through the air, birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.

Newton’s Third Law in Nature

Other examples of Newton’s Third Law

The baseball forces the bat to the left (an action); the bat forces the ball to the right (the reaction).

The reaction of a rocket is an application of the third law of motion. Various fuels are burned in the engine, producing hot gases.

The hot gases push against the inside tube of the rocket and escape out the bottom of the tube. As the gases move downward, the rocket moves in the opposite direction.

Other examples of Newton’s Third Law


Answer the following questions using the information you have learned about Newton’s Laws of Motion. Then click to check your answer.

1. What does Newton’s First Law of Motion state?

Answer: Newton’s First Law of Motion states that an object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless it is acted upon by an unbalanced force


2. What does Newton’s Second Law of Motion state?

Answer:According to Newton’s Second Law of Motion, acceleration depends on the object’s mass and on the net force acting on the object. This relationship can be written as an equation:

Acceleration NetForce

Mass


3. What does Newton’s Third Law of Motion state?

Answer : Newton’s Third Law of Motion states that if one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object.


Answer the questions using your knowledge of Newton’s Laws of Motion. Then click to see the answer.

1.Why do you feel pressed back into the seat of a car when it accelerates?

Answer:

Because of the First Law of Motion, which states that an object will remain at rest unless it is acted upon by an unbalanced force. Our body has the tendency to stay at rest, but later on goes with the car when it accelerates.


2. How could you keep an object’s acceleration the same if the force acting on the object were doubled?

An object’s acceleration will be kept the same when the force acting on the object is double only if the mass is decreased in half.


Answer:


3. According to Newton’s Third Law of Motion, how are action and reaction forces related?

Answer:The action and reaction forces are equal in strength but opposite in direction.


4. If you stack several metal washers on top of a toy car, and a heavy book on the floor near the car, what will happen to both the car and the washers if you roll the car into the book? Answer: According to Newton’s First Law of

Motion, the washers will continue to move forward while the car stops. The unbalanced force of the book on the car stops the car, but not the washers.


5. How can Newton’s Third Law of Motion explain the launching of a space rocket?

Answer: A rocket can rise into the air because the gases it expels with a downward action force exert an equal but opposite reaction force on the rocket.

Newton’s Laws of Motion in the Science

Lab Get together in your cooperative groups

and do the Science experiments with the different materials provided (toy cars, wooden blocks of different sizes, spring balances, construction paper, washers, etc.).

Remember to review all safety precautions and icons before beginning numerous activities in the lab.

Science Lab: What changes motion?

Stack several metal washers on top of a toy car.

Place a heavy book on the floor near the car.

Predict what will happen to both the car and the washers if you roll the car into the book.

Test your prediction.

Now, design other similar experiments and test them.


Directions: Click on the best answer using your knowledge about Newton’s Laws of Motion, to answer the following questions.


1. A car with a large mass uses more fuel than a car with a smaller mass while driving the same distance. Which law describes this situation?

a) First Law of Motion

b) Second Law of Motionc) Third Law of Motion

Incorrect

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Correct

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2. If clothes are on the floor of your room, they will stay there unless you pick them up. Which law describes this situation?



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Correct

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3. After you hit a tennis ball with a racket, it will continue to move through the air. Which law describe this situation?



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4. Inertia is another name for:



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5. If a speedboat pulls a 55 kg water-skier, causing him to accelerate at 2.0 m/s2, the force acting on the water-skier is 110 N. Which law describes this situation?



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6. The force of a person pulling a wagon and the mass of the wagon determine the wagon’s acceleration. Which law describes this situation?



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7. If you take things out of a wagon, and keep pulling with the same force, the acceleration of the wagon will increase. Which law describes this situation?



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8. When a gymnast does a flip, she pushes down on the vaulting horse. The vaulting horse pushes her up to complete the flip. Which law describes this situation?



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9. The kayaker’s paddle pulls on the water. The water pushes back on the paddle, causing the kayak to move. Which law describes this situation?



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10. When a dog leaps, it pushes down on the ground. The ground pushes the dog back into the air. Which law describes this situation?



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11. Which law does a magician apply when he pulls a tablecloth and keeps the objects on the table from moving?



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12. Look at the picture. Which law is it describing?



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13. Look at the picture.Which law is it describing?



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14. Look at the picture.Which law is it describing?



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15. If a student is pulling a bag of balls of 10 kg, and the acceleration is of 2 m/s2, what is the force exerted on the bag?

a) 20 N

b) 5 N

c) 12 N

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Congratulations!

You are now ready to take the written

assessment.

Congratulations!

You are now ready for your final group project.


Group ProjectDirections: Using what you have learned about Newton’s Laws of Motion, and working in collaborative groups, design and build a contraption that illustrates the applications of the laws.

Certificate of Mastery:


Congratulations!

Documents

Newton’s Laws of Motion Nancy S. Chu & Elizabeth Watson EDT 610: Instructional Design – Theory & Model Dr. Gladys Arome St. Thomas University June 24,