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Newton’s Third Law of Motion

If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object.

A:  Action-Reaction Force Examples

1.  A bird flies forward exerting a force on the air with its wings. The air pushes back on those wings with an equal force.

2.  The squid exerts a force on the water that it expels from its body cavity. The water exerts an equal and opposite force on the squid, causing it to move.

B.  Action-Reaction Forces

1.  Equal and opposite forces add to zero. In other words, balanced forces cancel out.

2.  Forces cancel out only when they are applied to the same object.

3.  Action-Reaction forces don’t apply to Newton’s third law because it applies to forces on 2 different objects.

C.  Momentum

1.  Momentum is quantity of motion.

2.  Momentum = Mass (kg) X Velocity (m/s)

3.  The unit of measure of momentum is (kg X m/s).

4.  Momentum of an object is in the same direction as the objects velocity.

5.  More momentum means the object is harderto stop.

D.  The Law of Conservation of Momentum

1.  The total momentum of any group of objects remains the same unless outside forces act on the objects.

2.  When 2 or more objects collide in the absence of friction (outside force), momentum is not lost.

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