# Physical Science Ch. 6 Forces are part of a mutual action called INTERACTION. WHERE IS THE INTERACTION IN THIS PICTURE?

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Physical Science Ch. 6

Forces are part of a mutual action called INTERACTION. WHERE IS THE INTERACTION IN THIS PICTURE?

NEWTON’S THIRD LAW STATES: Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.

Action VS. Reaction  ACTION  OBJECT A EXERTS A FORCE ON OBJECT B.  Example: hammer hits nail  REACTION  OBJECT B EXERTS FORCE ON OBJECT A  Example: nail hits hammer back

Boulder vs. Earth Example: Earth pulled up by boulder, boulder pulled to ground by Earth. We can see the boulder move, but why don’t we notice the Earth being pulled? MASS DIFFERENCES!! F / m = a Boulder, f /M= a Earth More mass, less acceleration

How do planes and birds fly? THRUST LIFT DRAG WEIGHT ACTION- REACTION FORCE PAIRS!!!!

Do action-reaction forces cancel? Only internal forces cancel! See below… hand pushes box so box pushes hand. BUT, they are external… so the box accelerates the hand and the hand accelerates the box!!!

Have you ever noticed that you can’t really push yourself? Forces exerted by one part of an object on another part of the same object are INTERNAL FORCES! Internal forces NEVER influence the acceleration of an object! Only external forces are responsible for acceleration!

Pg. 80-81 Horse-Cart Problem

Moral of the story according to Newton’s Third Law of Motion: If you push hard on the world, the world will push hard on you… if you push gently on the world, it will push gently on you! THE WAY YOU TOUCH OTHERS IS THE WAY OTHERS WILL TOUCH YOU!

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