Newton’s Third Law Review Homework Notes: Newton’s Third Law Third Law Video Homework: Newton’s Third Law Practice

1. What net force is required to accelerate a car at a rate of 2 m/s2 if the car has a mass of 3,000 kg? F = 6000 N M = 3000 kg A = 2 m/s/s

2. A 10 kg bowling ball would require what force to accelerate down an alleyway at a rate of 3 m/s2? F =30 N M = 10 kg A = 3 m/s/s

3. Sally has a car that accelerates at 5 m/s2 3. Sally has a car that accelerates at 5 m/s2. If the car has a mass of 1000 kg, how much force does the car produce? F = 5000 N M = 1000 kg A = 5 m/s/s

4. What is the mass of a falling rock if it produces a force of 147 N? F = 147 N M = 15 kg A = 9.8 m/s/s

5. What is the mass of a truck if it produces a force of 14,000 N while accelerating at a rate of 5m/s2 ? F = 14,000 N M = 2800 kg A = 5 m/s/s

6. What is the acceleration of softball if it has a mass of 0 6. What is the acceleration of softball if it has a mass of 0.5 kg and hits the catcher’s glove with a force of 25 N? F = 25 N M = 0.5 kg A = 50 m/s/s

7. Your own car has a mass of 2000 kg 7. Your own car has a mass of 2000 kg. If your car produces a force of 5000 N, how fast will it accelerate? F = 5000 N M = 2000 kg A = 2.5 m/s/s

8. Sally wants to accelerate even faster than in problem #3, so she removes 500 kg of mass from her car. How fast will her 1500 kg car accelerate if it produces 5000 N of force? F =5000 N M =1500 kg A = 3.3 m/s/s

9. Sally challenges you to a race 9. Sally challenges you to a race. On the first turn you run off the course and your car strikes a large bale of hay. Your car still produces 5000 N of force, but now it accelerates at only 2 m/s2. What is the mass of your car now that the bale of hay is stuck to it? F = 5000 N M = 2500 kg A = 2 m/s/s

10. Even tough she is way ahead of you, Sally switches her car to run on nitrous oxide fuel. The nitrous oxide allows her car to develop 10,000 N of force. What is Sally’s acceleration if her car has a mass of 500 kg? F =10,000 N M = 500 kg A = 20 m/s/s

Notes: Newton’s Third Law of Motion For every action there is an equal and opposite reaction.

Action  Reaction (draw the force pair and explain) Baseball player hits the ball with her bat. Action: Reaction:

Action  Reaction (draw the force pair and explain) Fish propel themselves forward by pushing water back, behind them. Action: Reaction:

Action  Reaction (draw the force pair and explain) Soccer player: When the boy runs up to the ball and kicks it, he applies a force to the ball, moving it forward. The ball reacts by pushing back against the boy, which he feels as pressure on his foot when he kicks the ball. ACTION: REACTION:

Newton’s 3rd Law of Motion If a hammer strikes a nail, the hammer exerts a force on the nail. The nail must also exert a force on the hammer since the hammer’s state of motion is changed and, according to the First Law, this requires a net (outside) force. For every action there is an equal and opposite reaction. If the hammer hits the nail with 5N of force, how much force does the nail push back with? ACTION: REACTION:

Newton’s 3rd Law: Try it Out! (Describe and draw the forces) Press the side of your hand against the edge of a table. Notice how your hand becomes distorted. A force is being exerted on it. Important point: You can only feel the forces being exerted on you, not the forces you exert on something else. It is the force the desk is exerting on you that you see and feel in your hand. If you push the desk with 2N of force, with how much force does the desk push you? Action: Reaction:

But why do objects react so differently if the force acting on them is the same? A bug smashes into a car windshield with 1N of force. The car pushes back with 1N of force. Whose change in motion (acceleration) is greater?

Explain. m x a = F = F = m x a

Notes: Newton’s Third Law When the force exerted by two objects is the same The object with the smaller mass will have a greater acceleration. The object with the larger mass will have a smaller acceleration.

A bat hits a ball. Explain. m x a = F = F = m x a

A person jumps. Explain. m x a = F = F = m x a

Assignment: Newton’s Third Law Product: Create a video with three examples of action-reaction pairs. For each example: Clearly SHOW and LABEL the Action/Reaction pair. F=ma equation for each object with letters appropriate size. A 2 sentence description explaining your pair using Newton’s 3rd Law of motion.

M x a = F = F = m x a Example 1: Equation: Wall Person Action: Person pushes on wall. Reaction: Wall pushes on person. Equation: Wall Person M x a = F = F = m x a Explanation: They wall and person both exert the same force. The person will accelerate more than the wall because the person has a smaller mass than the wall.

Homework: Newton’s 3rd Law Practice