Return to Physics IndexNewton's Third Law of Motion

John E. McCoy Douglass Math and Science Academy

543 N. Waller

Chicago IL 60644

(312)534-6176Objectives:

This lesson is for 7th and 8th graders.

Students will be able to do activities to demonstrate Newton's Third Law of

Motion.

Students will be able to explain Newton's law.Materials Needed:

1. dynamic carts

2. 100g weights-6

3. spring balances-3

4. fish line

5. rope

6. clamps-4

7. pulleys-2

8. meters sticks-10

9. scissors,tape,paper

10. blueprint of rocketStrategies:

Using the PHENOMENOLOGICAL approach, the teacher demonstrates Newton's Third Law

of Motion by placing a firecracker between two pop cans and lighting it. Also a

student is used to demonstrate force by having the student press against a wall

(action) and the wall presses against the student (reaction). Also the teacher

pushes down on the student's arm (action) and the student's arm moves upward.

Students move to the various stations to do the activities.

Station 1-Balloon Race

A fish line is extended from two ring stands for the race. The students use

tape to attach the balloons to the straw. The fish line is pushed or threaded

through the straw. The balloon(s) is/are blown-up and the end is pinched or

closed. The students release the balloons. The air comes out the end of the

balloon (action) and the balloon moves forward (reaction). The distance

traveled is measured in meters.

Station 2-Spring Balances and Weights.

A demonstration of equal force being exerted on a spring balance is set-up for

the students. There are two 200g weights attached to each end of the balance.

The students are asked to guess the weight on the balance. Later the students

will vary the number of weight and check the reading on the balance to see if

the amount of force is the same (equal). The weights are pulling downward on

the balance scale (action) and the scale is pulling on the weights (reaction).

Station 3-Dynamic Carts

Two carts are placed end to end and a trigger is released where one cart hits

the second cart (action) and the second cart moves backward (reaction). Both

carts move backward equal distances because the masses are the same. However,

if the masses are varied 2x, 3x or 4x, the students will get some interesting

results about the distance that each cart will travel.

Station 4-Roller Skates

Two students, both on roller skates, will pull on a rope and the other students

will observe which student moves the greater distance.

Station 5-Rocket Launching

Using blueprints, the students make rockets for launching. The pieces are put

together with tape. The rockets are launched by using a straw to blow into the

open end.Conclusions:

1. Students will discover that the activities dealt with forces.

2. Students will discover that the two forces, action and reaction, are equal in

magnitude and opposite in direction.

3. The student will discover that the motion of the forces must be in a straight

line.

4. Students would have discovered Newton's Third Law of Motion using the

PHENOMENOLOGICAL approach.