What You Should Know About
The Physics of Driving

Codman Academy Charter Public School
Physics 10A | 2004-2005
Teacher: Regan Brooks
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Newton's Third Law
Newon's Third Law
examples of action reaction pairsFor Every Action there is a Reaction

 What does Newton's Third Law tell us?

Newton's third law tells us that when you push against something it pushes back on you with an equal and opposite force. Newton's 3rd law is the law of action and reaction. It tells how forces interact with each other. The forces are the action force and the reaction force. There will be a reaction force even if the object is non-living.

Here are 5 examples of action and reaction forces:

1.When you push on a wall the wall pushes back on you.

2. When you walk on the the ground, you push the ground and the ground pushes you.

3.When the bat hits the ball the ball hits the bat.

4.When your finger touches your nose your nose touches your finger.

5. When you push on a table the table pushes on you.

It takes two objects to make an action and reaction pair. An action and reaction force can not act on one object. It takes two to tangle!

How does the third law apply to driving?

Newtons 3rd law applies to driving because when you drive the action force is the pushing against the road and the reaction is the road pushing against the tires. Also when a car hits a person, the person hits the car. When a car hits telephone pole the pole hits the car. When a car hits a wall the wall hits the car. Another example of Newton's 3rd law would be that when a person's foot pushes the gas pedal, the gas pedal pushes the person's foot.

Why is driving on icy roads so difficult?

It is difficult to drive on a icy road because the tire can not grip the road because there is less fiction. So when the car tries to push on the road it can not because the road is icy. If the car can't push on the road, the road can't push on the car. As a result the car slides in the ice.

Another way that Newton's 3rd law is involved is that if two cars with different mass were driving on an icy road and they couldn't stop they would crash into each other. If this happens, the force acting on both cars would be the same, but the acceleration for the car with the smaller mass would be greater. The acceleration from the car with the bigger mass would be less than the other car it crashed into.
If the same two cars with different masses crash head on in a collision they would have the same force of impact and the the same impulse. The difference between the two cars would be the resulting acceleration because the masses are not the same.


Take A Quiz on Newton's Third Law!!
To take this quiz online, please click here: http://www.codmanacademy.org/moodle/mod/quiz/view.php?id=442

Newton's Third Law Of “Motion”

What is Newton's Third Law about?
B. What ever is in motion stays in motion
C. Action-Reaction Forces
What happens to the wheels of a car on an icy road?
A. The wheels on the car can't grip the road
B. The wheels don't move
C. The wheels fall off

Which of the following pairs are action-reaction pairs?
A. The sun shines and the snow melts
B. The ball hits the window and the window breaks
C. Jenna pushes on the table and the table pushes on Jenna

What do we call the forces that constitute an interaction in Newton's 3rd law?
A. Action-Reaction forces
B. Force-Interaction forces
C. Horse-Cart forces
D. Jenna-Joya Forces

Inanimate objects can exert forces.
A. True
B. False

What happens when 2 cars with different masses have a head-to-head collision?
A. The car with less mass has a greater time of impact.
B. They experience the same force of impact.
C. The cars just bounce off each other.

If  two cars with different masses experience the same Force of Impact and the same impulse then what would be different?
A. Change of momentum
B. Time of impact
C. Momentum
D. Acceleration

If you push on something, it....?
A. pushes back on you.
B. doesn't moves.
C. falls.
D. swings.

If you have on rollerskates and you push on a wall, what will probably happen?
A. You fall.
B. You roll back.
C. You crash into the wall.
D. You slip and DIE.

A person touches his/her nose and his/her nose touches back.
A. True
B. False

Action Force: Book pushing on table & Reaction Force: Table pushing on book

A Handy Hands-on Game

What you'll need: 
    Two volunteer students
What to Do:

    Extend one hand out and press against the wall. Then extend hand out in mid air and press.  Your body will lean over with nothing to support it.  This happens because there is not another object to exert an equal force on you but with the wall you don't fall over is because there is something pushing back on you. Stand facing each other about one arm's length from your partner. The trick is to make your partner move their feet by pushing only on the hands.  Each participant should stand with their feet together and one hand behind their back. 

Step 1:
    Hold up your hand in front of you at shoulder height, palm facing your partner.  Tell your partner to push against your hand (but don't push back).

Step 2:
    Your partner pushes again and you pull your hand back. (Repeat until one partner moves his feet.)

What to notice:
Step 1:    
    That the person doesn't move

Step 2:   
    Whenever one body (object) exerts a force on a
     second body (object), the second body (object)

     exerts an equal and opposite force on the first

     body (object).

What's going on:
Step 1:
    Because of equal forces and because the person pushes on the wall and the wall pushes on the person.

Step 2 & 3:
    Because both people are exerting the same amount of force niether moves.   

Further Question: 1. Why do we say that forces occur in pairs?


This was written by Mitzie Wilkins from Chicago, IL

Newton's Third Law Resources
The name of this website is The Physics Classroom. This lesson is Lesson 4: Newton's Third Law of Motion.


This website teaches you how to Identify Action and Reaction Pairs.

This website teaches you about Newton's Laws of Motion.

This website teaches you about Reaction Force.

This website teaches you about how Newton's Third Law states that "Every Action has an equal and opposite Reaction".

A man is pushing on the woman and the woman is pushing on the man

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