N EWTON ’ S THIRD LAW OF MOTION Action/Reaction Pairs

R EVIEW : N EWTON ’ S 1 ST & 2 ND L AWS 1. Give a real life example of Newton’s 1 st Law of Motion. 2. What is another name for Newton’s 1 st Law. 3. What formula is associated with Newton’s 2 nd Law of Motion? 4. Give a real life example of Newton’s 2 nd Law of Motion.

O H N O – F LYING B ALLOONS ! What caused the balloon to fly across the room? Does it have an engine? Is it being pulled by an invisible string?

N EWTON ’ S 3 RD L AW OF MOTION For every action force, there must be an equal and opposite reaction force. Forces occur in pairs. Action Forces Reaction Forces

A N EXAMPLE OF A CTION /R EACTION P AIRS. action force. When a person jumps on a trampoline, he or she exerts a downward force on the trampoline = action force. reaction force The trampoline then exerts an equal force upward, sending the person high into the air = reaction force.

N EWTON ’ S 3 RD L AW IN N ATURE What action/reaction forces cause a fish to propel through the water when they are swimming?

L ET ’ S E XPLAIN …. action force reaction force Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards (action force). In turn, the water reacts by pushing the fish forwards (reaction force), 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).

H OW DO BIRDS FLY ? What action/reaction pair allows a bird to fly through the air? Why can’t we fly?

L ET ’ S E XPLAIN … Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. In turn, the air reacts by pushing the bird upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards). Action-reaction force pairs make it possible for birds to fly.

O NE MORE EXAMPLE …R OCKETS ! 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.

I DENTIFY AND EXPLAIN ANY ACTION / REACTION PAIRS IN THE PICTURE BELOW.