Newton’s 3 rd Law 11/27/13

Newton Hat Trick Video

Background Information Newton’s Law of Universal Gravitation  The Principia - Mathematical Principles of Natural Philosophy  Newton’s three laws of motion is the foundation for his Law of Universal Gravitation

Newton’s Laws Quick Summary  1 st Law:  An object at rest stays at rest  An object in motion stays in motion with the same velocity, if no net force  2 nd Law:  Accelerations are do to the net forces on an object (mass)  3 rd Law:  Action and reaction pair of forces

Newton’s 3 rd Law (recap)  Law III: To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions.  When one body exerts a force on a second body, the second body exerts an equal and opposite force on the first.  TWO objects and TWO forces  Forces always come in pairs

Newton’s 3 rd Law  TWO Forces and TWO objects (TWO different F.B.D.)  IF object A pushes/pulls on object B THEN object B pushes/pulls on object A in the opposite direction  Object A push/pull – Action Force  Object B push/pull – Reaction Force

Newton’s 3 rd Law Examples  The action force will be stated  Identify the reaction force  Draw the reaction force vector

Newton’s 3 rd Law Examples  Flower pulls on hand

Newton’s 3 rd Law Examples  Ball hits the bat

Newton’s 3 rd Law Examples The Earth pulls on the skydiver.The skydiver pulls on the Earth.

Newton’s 3 rd Law Examples  Draw a F.B.D. of both objects and identify the action force and reaction force.  Mr. Z. kicks a ball across to floor. What is the action force and reaction force?  Action Force: Mr. Z. kicking the ball.  Reaction Force: The ball pushing on Mr. Z.

Free Body Diagrams  Mr. Z.  Tennis Ball

Newton’s 3 rd Law Examples  One last example …  This one is simple but a bit tricky!

Newton’s 3 rd Law Examples  You (a student) sitting in a chair.  What are the action forces (two)?  1) The Earth pulling you down  2) You pushing on the chair  These are both ACTION forces!  What are the reaction forces?  1) You pulling on the Earth  2) The chair pushing on you

Free Body Diagrams

Homework  Newton’s 3rd Law Practice  Due Tues. 12/3/13  If you need Bridge Analysis vocab words – there are 3 glossaries on the cart