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Newton’s 3 rd Law of Motion. Newton’s 3 rd Law. For every action there is an equal and opposite reaction. Examples. Hammer and Nail:
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Newton’s 3rd Law For every action there is an equal and opposite reaction
Examples • Hammer and Nail: • As a hammer hits a nail, the hammer applies a force to the nail AND the nail applies a force on the hammer this is why the hammer slows down as it hits the nail • Rocket blasting off the launch pad: • As the rocket applies a thrust force downward, the rocket moves upward
ALL FORCES COME IN PAIRS They are known as: “action-reaction pairs”
“Action-Reaction Pairs” Object A applies an “action” force on Object B while at the same time Object B has a “reaction” force on Object A of equal magnitude but opposite direction.
That’s a lot to write out… • It can be shortened with a formula! • FAB = -FBA • In English this simply says the Force that Object A puts on Object B is equal but opposite (remember: the negative just means opposite direction) to the Force that Object B puts on Object A
Why is it so difficult? • There is no action-reaction pair! • You need the bending “action” to have the jumping “reaction”.
Think, pair, share (Think about it yourself, talk it over with a partner, and then write your ideas in your notes): Use Newton’s 3rd Law of Motion to explain to a classmate why it hurts when you punch a wall.
Can a wall really punch you back? YES! Well, in a way…
How? • The wall applies a force that is exactly equal in magnitude but opposite in direction. • This “reaction” force is known as a negative force; remember the negative just refers to the fact that it is opposite in the direction it goes
Check YOUR Understanding A truck driving down the road hits a mosquito. The mosquito is smashed and the truck continues driving. Which of the two forces is greater: The mosquito on the truck or the truck on the mosquito? Why? (Hint: really think about Newton’s 3rd Law here and maybe even think back to Newton’s 2nd Law to answer “why?”)
When you think you have the answer… Use your Peer-to-Peer Network toask a classmate (that has already completed this question) if your answer matches theirs