Newton’s 3rd Law & Momentum

Think about it… Why to firemen’s hoses have large handles at the nozzle? Why would it be wise to secure your boat BEFORE you jump onto the dock rather than just after. If you fire a gun, why should you brace yourself?

the 3rd Law For every action force, there is an equal and opposite reaction force. Forces always occur in pairs. If object A applies a force to object B, then object B will apply an equal force in the opposite direction to object A.

Examples of Newton’s 3rd Law When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.

Examples of Newton’s 3rd Law There are two forces resulting from this interaction the action force-your force on the chair the reaction force - the chair applying a force on your body.

Another example of Newton’s 3rd Law The baseball applies a force to the bat to the left (an action); the bat applies a force to the ball to the right (the reaction).

More examples of Newton’s 3rd Law A fish moving through the water uses its fins to apply a force to the water. The water reacts by applying a force to the fish, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards). Fish swimming

More Examples…ouch As you watch the following video clip, think of “action- reaction force pairs”. http://dsc.discovery.com/videos/storm- chasers-new-dominator-protection.html

Apply Newton’s 3rd Law to this example. What is the action force in this example? What object is the force being applied? What is the Reaction force in this example? What object is the force being applied?

Another example of Newton’s 3rd Law The reaction of a rocket is an application of the third law of motion. Various fuels are burned in the engine, producing hot gases. The hot gases push against the inside tube of the rocket and escape out the bottom of the tube. As the gases move downward, the rocket moves in the opposite direction. Rocket to Mars

How is momentum related to Newton’s laws? Momentum is the product of mass and velocity. p=m v When 2 object collide, momentum is conserved. (Momentum is not lost. It is transferred)

Momentum Demonstration… Think about which has more momentum? Tennis Ball fast Tennis Ball slow Bowling ball fast

Momentum Demonstration… Which was hardest to control? Why? Rank from most to least momentum.

Momentum Demonstration… Could you relate the 1st Law to this demonstration? 2nd Law? 3rd Law?