Physics 1100 – Spring 2012 Chapter 5 – Newton’s Third Law Forces and Interactions Newton’s Third Law Vectors

Physics 1100 – Spring 2012 Newton’s 3 rd Law For every action (force), there is an equal and opposite reaction (opposing force). Force on Newton by Einstein = Force on Einstein by Newton (But their accelerations need not be the same: Newton tries to outsmart Einstein by loading his own cart with lead bricks)

Physics 1100 – Spring 2012 Action - Reaction

Physics 1100 – Spring 2012 Action - Reaction

Physics 1100 – Spring 2012 Action - Reaction

Physics 1100 – Spring 2012 Action - Reaction

Physics 1100 – Spring 2012 Why Do We Move?

Physics 1100 – Spring 2012 Why Do We Move?

Physics 1100 – Spring 2012 Action – Reaction and Rockets

Physics 1100 – Spring 2012 Action - Reaction

Physics 1100 – Spring 2012 Rockets Further investigation and experimentation have confirmed the findings of Isaac Newton in the 17th century and it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error for after the rocket quits our air and really starts on its longer journey, its flight would be neither accelerated nor maintained by the explosion of the charges it then might have left. To claim that it would be is to deny a fundamental law of dynamics, and only Dr. Einstein and his chosen dozen, so few and fit, are licensed to do that. …..That Professor Goddard, with his "chair" in Clark College and the countenancing of the Smithsonian Institution, does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react--to say that would be absurd. Of course he only seems to lack the knowledge ladled out daily in high schools. NYT, January 13, 1920 NYT, July, 1969

Physics 1100 – Spring 2012 Newton’s Third Law

Physics 1100 – Spring 2012 Forces are Vectors so Directions are Important Force #1 Force #2 Force #1 Force #2 Total Force = 0 Total Force

Physics 1100 – Spring 2012 Vectors Adding Vectors

Graphically Adding Vectors Physics 1100 – Spring 2012 aaa b b c a c b

Physics 1100 – Spring 2012 Vector Addition

Physics 1100 – Spring 2012 Vector Addition of Forces

Physics 1100 – Spring 2012 Vector Addition of Forces

Physics 1100 – Spring 2012 Vectors

Physics 1100 – Spring 2012 Components

Physics 1100 – Spring 2012 Clicker Question An archer shoots an arrow. Consider the action force to be exerted by the bowstring against the arrow. The reaction to this force is the A) friction of the ground against the archer's feet. B) air resistance against the bow. C) grip of the archer's hand on the bow. D) combined weight of the arrow and bowstring. E) arrow's push against the bowstring. Arnold Strongman and Suzie Small each pull very hard on opposite ends of a massless rope in a tug-of-war. The greater force on the rope is exerted by A) Suzie, surprisingly. B) Arnold, of course. C) both the same, interestingly enough.

Physics 1100 – Spring 2012 Clicker Question The attraction of a person's body toward the Earth is called weight. The reaction to this force is A) the person's body pulling on the Earth. B) the person's body pushing against the Earth's surface. C) the Earth's surface pushing against the person's body. D) none of these. A Mack truck and a Volkswagen traveling at the same speed have a head-on collision. The vehicle that undergoes the greatest change in velocity will be the A) Volkswagen. B) Mack truck. C) same for both.

Physics 1100 – Spring 2012 Clicker Question A horse exerts 500 N of force on a heavy wagon. The wagon pulls back on the horse with an equal force. The wagon still accelerates because A) the horse pulls on the wagon a brief time before the wagon reacts. B) nevertheless there is still an unbalanced force on the wagon. C) the wagon does not accelerate because these forces are equal and opposite. D) these forces are not an action-reaction pair. E) the wagon is not alive. A car traveling at 100 km/hr strikes an unfortunate bug and splatters it. The force of impact is A) greater on the bug. B) greater on the car. C) the same for both.