Learning a law of physics – PHYS 1010

Part 3 : Learning about a Law of Physics

Newtons 3rd law of motion states for every action there is an equal and opposite reaction. Or To every action there is always an opposed equal reaction.

This means that every time a force acts on an object, there is an equal but opposing force also action on the object. This is the theory involved in the application “Newtons Cradle” which is probably the most well known desk toy ever created. Grab two balls, pull them back, and once they hit the remaining three, two balls react on the other side of the cradle, and produce the opposite action of the balls dropped initially.

Three great examples of this law of motion are as follows:

  1. When you drop an object from any height, the gravity of the earth pulls on the ball, and the ball pulls on the earth. This can be illustrated with trajectory over time, distance, and direction. Simply dropping ice into your whiskey and coke is a perfect example of this.

  2. Another well known example of this is a car moving down the road. The tires push on the road, as the road pushes back on the tire. This done in the context of circular force is illustrated as momentum by the vehicle.

  3. When a bug collides with an oncoming vehicle the force the bug exerts on the windshield, is exact and opposite to the force the windshield exerts on the bug even though the mass, and velocity of the vehicle might be much greater.

  4. Last but not least, when we launch a rocket the combustion of fuel creates force by the rocket pushing on the exhaust gas, and the gas pushing opposite on the rocket.