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Chapter 12 Lesson 3 Newton’s 3 rd Law of Motion a.k.a. - Action and Reaction

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I. Newton’s 3 rd Law A.Def – to every action, there is an equal and opposite reaction 1. Forces come in pairs 2. Ex: Firing a gun or cannon 3. How does a swimmer in the pool use Newton’s 3 rd law of Motion? 4. Action-reaction pairs do not cancel out…they act on different objects.

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Group Problem 1. Explain why jumping from a “john” boat to a dock is much more difficult than jumping from a barge to a dock? Explain using arrows to represent forces. You may also draw a picture.

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II. Momentum A.Def – the property of a moving object due to its mass and velocity (speed). 1. Units kg x m/s 2. Rolling Demo 3. Formula = momentum (p) = mass (kg) x velocity (m/s) 4. Ex: 2 bumper cars are headed for a collision. Car #5 is traveling at 1.6 m/s and has a mass of 120 kg. Car #1 is traveling at 1.09 m/s and has a mass of 175 kg. Which car will “bump” the other car back?

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#5 (p = m x v) 120 kg x 1.6 m/s = 192 kg m/s #1 (p = m x v) 175 kg x 1.09 m/s = kg m/s

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B.The Law of Conservation of Momentum 1. Def - all momentum is transferred between objects. 2. Ex: Tennis Ball and Basketball Demo 3. Ex: Playing pool 4. Ex: Tackling in football

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5. Does this make sense? (Assume no friction) Cue ball 10 kg x m/s ball 1 1.55 kg x m/s ball 2 1.36 kg x m/s ball 3 2.25 kg x m/s ball 4 1.14 kg x m/s ball 5 2.89 kg x m/s ball 6 0.40 kg x m/s ball 7 0.41 kg x m/s

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12.3 wks (on separate sheet of paper) 1.What is the momentum of an 80 kg runner moving at a speed of 3.5 m/s? 2.Another runner who has mass of 650,000 g is running at a speed of 4.2 m/s. What is the momentum of the runner? 3.If runner #1 collides with runner #2 who will win the collision? 4.A ball has a momentum of 32 kg x m/s. What is the mass of the ball if it is traveling at 43 m/s? 5.What is speed of a ball that has a mass of 48 grams and has a momentum of 38 kg x m/s?

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