Action and Reaction

Mitzie Wilkins Enrico Fermi Elementary School
1415 East 70th Street
Chicago, Il 60637
(312) 535-0540

Experiment 1 Needed:

One volunteer student


To demonstrate that forces occur only in pairs


Have Newton's third law of motion written on the board. Make a brief
introduction on Sir Isaac A. Newton and have the whole class read the law.

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).

A Handy Hands-on Game First, extend one hand out and press against the wall. Next, extend hand out in mid air and press. Your body will lean over with nothing to support it. Ask students to explain what happened. Request one volunteer to come to the front of the class. Tell the volunteer that he or she will be your partner in a demonstration to experiment with Newton's third law of motion. Stand facing each other about one arm's length from your partner. The trick is to make your partner move his feet by pushing only on the hands. Each participant should stand with his feet together and one hand behind his back. Step 1:
You hold up your hand in front of you at shoulder height, palm facing your
partner. Tell your partner to push against your hand (you do NOT push back).

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

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

Answer: Every action has a reaction counterpart (or partner).


Experiment 2 Materials Needed:

1 skate car with propeller fan
6 size C batteries
3 cardboards - sizes: large, medium and small


To experiment with the law of action force and reaction force

To sail the skate car or
not to sail the skate car
that is NOT the question!

Question: What do you think would happen if you put various size sailboards on a
propelling skate car?

Strategy: Have class break up into small groups of 3 or 4 members and select a spokesperson. Explain the mechanisms (parts) of the skate car. Demonstrate how the skate car works. Next, hold the large sailboard in front of the skate car approximately 2" away from the fan. Ask students what they think will happen if you turn the fan on. Allow them time to think and discuss the question within each group (approx. 1 or 2 mins.). Regain the students' attention. Ask each spokeperson what her group decided would happen. After all predictions are in, say: "Well, let's put it to the test!" Turn the fan car on while every one observes the results. Ask what happened and why do they think it occurred. Next, put the medium size sail in front of the fan, this time attaching it to the skate car. Ask the groups what they think will happen this time and follow the same procedure. Finally, do the same with the small sail. Discussion: Newton's third law of motion on action and reaction.


Put a scoreboard on the chalkboard and select a student to keep score on group

| The skate car will move | Right | Left | Will Not Move | | | | | | | Group 1 | | | | | | | | | | Group 2 | | | | | | | | | | Group 3 | | | | | | | | | | Group 4 | | | |
Return to Physics Index