Newton’s Third Law of Motion

Objectives

State Newton’s third law of motion

Identify action and reaction forces

Explain how forces come in pairs

WATCH THE MOVIE CAREFULLY AND ANSWER THE BELOW QUESTIONS:

1. What do we call the force that pulls the ball downward?

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2. In what direction the object accelerates ? Explain your answer.

-------------------------------------------------3. What happens when the ball

reaches the ground?-------------------------------------------------3. What causes the ball to bounce

when it reaches the ground?-------------------------------------------------4. Why does the green box stay at

rest?------------------------------------------------5. Conclude-------------------------------------------------

Now Look at the figure below and answer the questions:

1. When the balloon is emptied from air, in which direction the balloon pushes the air?

-----------------------------------2. In what direction, the

air pushes the balloon? How do you know?

-----------------------------------3. Conclude.-----------------------------------

Conclusion When an object exerts an

action- force on a second object, the second object reacts by exerting a reaction –force on the first object which is equal in magnitude but opposite in direction to the action force.

In other words, for every action there will be a reaction and forces act in pairs.

This is Newton’s Third Law of motion.

The figure below shows Apollo 11 roaring toward the moon in 1969:

Answer the questions below: Apollo 11

1. What is the action force exerted on Apollo 11?

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2. In what direction should be the reaction of engine to accelerate Apollo 11 upward?

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3. If Apollo ‘s mass is 200,000 kg, find the magnitude of the action force exerted on Apollo 11?

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4. Estimate the reaction force of the engine

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The figure below shows a rocket launched in the space:

Answer the following questions: Rocket mail

1. The gases produced are expelled by the engine from the back of the rocket. What is the action force exerted on the rocket?

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2. What will be the reaction force exerted on the rocket? In what direction?

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For each of the following figures, identify the action force and the reaction force, show the direction of the forces

Identify the action and reaction forces in the figures below, show the direction of the forces

CAN YOU EXPLAIN HOW A BIRD FLIES?

Answer: The bird when he moves his wings , he pushes the air downward ( action) , the air exerts a force upward ( reaction ) lifting the bird .

DO NOT FORGET:

1. Forces work in pairs: for every action there will be a reaction which will have the same magnitude as the action force but in opposite direction.

2. This statement represents Newton’s third law.

For Next time

Solve chapter review + standardized practice test textbook p: 94-96

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Quiz on Thursday : Newton’s first and second law.