By Donovan Miller Nathan Yoder Javier Aranguren Amelia Spilde Newton’s Third Law

Major Concept Newton’s Third Law of Motion states that whenever one object exerts a force on a second object, there is an equal and opposite force on the first object.  These forces are called action forces and reaction forces.  Since these forces are equal, it does not matter which is the action force and which is the reaction force.  Because of this, one force cannot exist without the other.

History Newton's third laws first appeared in his masterpiece, Philosophiae Naturalis Principia Mathematica (1687), commonly known as the Principia.  

Ideas in action Try and visualize if a fight broke out between Mr. GH and Mrs. Lange. They were arguing over the best way to solve quadratics and Mrs. Lange punches Mr. GH right in the calculator. When her fist hits his calculator, it exerted a force that was also returned by the calculator Other good examples of Things that demonstrate Newton's Third Law are advanced space rockets, missiles, scales, and general movement.

Think and explain 1. The earth does exert the same force on the sun because the force exerted is equal and opposite. 2. On carpet there is more force caused by friction which makes walking easier than on a smooth floor that your foot would slide onto. 3. This is so because when you walk on the log equal force is exerted in the opposite direction causing it to move backwards. 4. Yes it does but because of the vast difference in mass the earth's acceleration is miniscule

Think and explain 5. When you push downward the opposite force will lift you up which will make the scale read less weight. When you pull upward on the sink the opposite force will push you downward which will make the scale read more weight. 6. The reaction counterpart is the exact same amount of force pushed back onto the earth but because of the earth's mass it doesn't accelerate nearly as fast as the satellite. 7. The earth's mass compared to the satellite's is vastly lager which makes the earth still accelerate towards the satellite, but the acceleration is so miniscule that the earth does not go into orbit. 8. The scale would read zero because both of the sides equal out.

Think and explain 9. The impact force is the same on the truck and on the bike. The bike however will have a greater change of motion due to its small mass compared to the big truck. 10. The force that propels the rocket is the opposite reaction caused by the constant firing of the engine. The gas that comes out of the rocket  provides thrust in the opposite direction which propels it. 11. The gun and bullet have different masses. This allows the bullet to accelerate at a fast pace where as the gun accelerates at a much slower pace. 

Review Questions 1-What evidence can you cite to support the idea that a wall can push on you? A wall can push you if you exert certain amount of force on it. 2-What is meant by saying that a force is due to an interaction? A force is nothing itself, but is due to an interaction between one thing and another. 3- when a hammer interacts with a nail, which exerts a force on which? The hammer  exerts force against the nail, but is itself halted in the process. the same interaction that drives the nail also slows the hammer. 4-when a hammer exerts force on a nail, how does the amount of force compare to that of the nail on the hammer? Same; both are part of an interaction. 5-why do we say that force occur only in pairs? According to Newton's third law, for every action force there is an equal (in size) and opposite (in direction) reaction force. Forces always come in pairs. 6-When you walk along a floor, what exactly pushes you along? In order to walk on a floor (or any other surface), your foot must push backward on the floor (action force), so that the floor pushes you forward (reaction force). The force that your foot (and the floor) exert on each other is a friction force (between the sole of your shoe and the floor).

Review Questions 7-When swimming, you push the water backward, call this action. Then what exactly is the reaction force? The water pushes you forward as you accelerate through the water with the same impulse you used to push on the water. 8- If action is a bowstring acting on an arrow, identify the reaction force. The arrow pushes back on the bowstring. 9-When you jump up, the world really does recoil downward. Why cannot this motion of the world be noticed? Due de difference between the mass of the earth and yours. 10-when a rifle is fired, how does the size of the force of the rifle on the bullet compared to the force of the bullet on the rifle? How do the accelerations of the rifle and the bullet compare? Defend your answer. The forces are the same, equal and opposite, the rifle will recoil. 11- Since action and reaction are always equal in size and opposite in direction, why don't they simply cancel one another and make net force greater than zero impossible? These forces do not cancel because they influence the motion of different objects.

Review Questions 12/A-Besides the force of gravity, how many forces are exerted on the cart? Two, the horse pulling the cart forward and friction pulling the cart backwards. 12/B-What is the net horizontal force on the cart?  Force of pull of horse forward. Force of friction on cart backwards. 13/A-How many horizontal forces are exerted on the horse. Two: floor pushing horse forward, and cart pulling back the horse (due to friction of the cart).  13/B-What is the net horizontal force on the horse?  Ffp - Fpc 13/C-How many horizontal forces are exerted by the horse on the other objects? Ans. Two. One on the ground and one on the cart. 14/A-How many horizontal forces are exerted on the horse-cart system? The force pulling the system forward and the friction holding the system back. 14/B-What is the net horizontal force on the horse-cart system? Fp, Ft . 15-In order to increase its speed, why must the horse push harder against the ground than it pulls on the wagon? Otherwise the net force would be zero and no acceleration would happen.

Review Questions 16- If you hit a wall with a force of 200 N, how much force is exerted on you? Same force that was thrown on the wall, 200 N. 17-You can't hit a feather mid air with a force of 200 N, because the feather cannot hit back with that much force. 18-How does the saying "you get what you give" relate to Newton's tird law? Because for every action there is an equal and opposite reaction.

Background Information Newton's third law states that "Every action has an equal and opposite reaction." Which means that when you exert a force on an object, the object will exert the same force on you, such as a wall. When you lean against a wall, that wall, though it may not seem like the wall, is pushing you, but if it wasn't you would be falling through. This is an example of Newton's third law, as you are exerting as a force on the wall and the wall, in turn, is exerting a force back onto you.

Question/Hypothesis How will we demonstrate and measure Newton's Third Law with a Newton's cradle?

General Statement  We will use a Newton's Cradle, otherwise known as Newton's Balls or Executive Ball Clicker, to demonstrate the action and reaction.

Apparatus Newton's Cradle 2 Rulers

Step By Step 1. Place Newton's Cradle on flat area and pull one of the balls out to the side.  2. Measure by holding ruler horizontally to Newton's Cradle, then record distance away from cradle as initial force.  3. Release Ball and quickly move ruler to other end of cradle, holding it horizontally to cradle and measure distance, record as resulting force at highest point. 4. Repeat steps 1-3 twice more.  5. Compare measurements, taking into account that friction is a factor and the second measurement may be equal to or slightly less than the initial measurement. 

Safety Precautions? None for this demonstration