Newton's Third Law of Motion as a Science Project


The simplest statement of Newton’s Third Law of Motion is that for every action there is an equal and opposite reaction. Since this law’s introduction by Isaac Newton in 1687, it has been a cornerstone of physics, governing the expected results when any force is applied to an object in motion. There are several science projects that can easily be based on this important scientific law.

Third Law of Motion Basics

  • Newton’s Third Law of Motion relates to forces and their effect on masses that they contact. All masses that come into contact with each other, whether through direct contact by touching or indirect contact as the result of a force like magnetism or gravity, must affect each other.

    The equal and opposite reaction part of the Third Law means that the forces caused by each interacting object are equal in magnitude but opposite in direction. Newton, in his First Law of Motion, defined force as being equal to mass multiplied by acceleration (F = ma). The force on a large mass will result in a small movement, while that same force acting on a small mass creates a large movement.

    In its simplest form, the Third Law of Motion refers to two objects in direct physical contact with each other. However, any number of masses can interact under the Third Law of Motion. More complicated analysis is needed for such interactions.

Tug-of-War Experiment

  • The most basic experiment you can do to test Newton’s Third Law of Motion is a variation on the game of tug-of-war. Have two people stand on either end of a rope that they hold in their hands. When one person tugs on the rope, the other person is pulled in that direction. If both people pull the rope at the same time, each will feel a tug in the opposite direction of their pulling. If the two people are of significantly different weights, you can test to see how a small amount of force from the bigger person results in a great deal of movement for the smaller person.

Rolling Balls Experiment

  • You can perform another simple experiment using a collection of balls. You should have at least two balls of the same size and mass, as well as several other balls of varying sizes and masses. Roll the balls along a flat surface toward each other. When the balls collide, watch the results of the collision. When the two balls are the same mass and travel at the same speed, they should simply reverse their motion upon impact. Vary the speed of the balls’ travel to produce different forces from identical balls. Test the impact of balls of differing masses as well. Following impact, larger mass balls will move less than smaller mass balls. They will, however, continue to follow Newton’s law and will move in opposite directions with equal total force.

Rocket Wagon Experiment

  • A final activity to demonstrate Newton’s Third Law of Motion is a simulation of rocketry. You can create your own “rocket” using a wagon and a fire extinguisher. Have the rocket pilot sit in the wagon, holding the extinguisher. Point the extinguisher in the air behind the wagon and pull the trigger. The quick release of gas and extinguisher foam will cause the mass of the wagon to move in the opposite direction. Exercise caution when performing this experiment, and make sure there are no obstacles for the wagon or the extinguisher to hit.


  • Photo Credit Hemera Technologies/ Images
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