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NEWTON’S LAWS OF MOTION

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LAWS OF MOTION

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INERTIA ACCELERATION ACTION-REACTION

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NEWTON’S FIRST LAW

The Law of Inertia

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WHAT DOES THE WORD “INERT” MEAN?

“Inert” basically just means “unmoving” or “motionless”.

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NEWTON’S FIRST LAW STATES:

  • “Objects in motion will remain in motion and objects at rest will remain at rest, unless acted upon by an unbalanced force.”

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INERTIA

  • Definition: “The tendency of an object to resist change in motion.”
    • Objects that are moving will keep moving.
    • Objects that are not moving will stay still.
  • The more mass something has, the more inertia it has!

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WHAT IS AN UNBALANCED FORCE?

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https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html

TUG OF WAR

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PRACTICE!

  1. Mr. Findysz leaves his keys on his desk. You take his keys and steal his car. You are on a joy ride around town when a poor little puppy runs out in front of the car. The car will really hurt the puppy if you hit it. You can slam on the brakes, but that may not work in time. According to Newton’s First Law, why not?

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PRACTICE!

  1. Mr. Findysz leaves his keys on his desk. You take his keys and steal his car. You are on a joy ride around town when a poor little puppy runs out in front of the car. The car will really hurt the puppy if you hit it. You can slam on the brakes, but that may not work in time. According to Newton’s First Law, why not?

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Answer: The car is an object in motion. Because the car has a lot of mass, it also has a lot of inertia. Because it has a lot of inertia, it is really hard for it to change its motion.

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NEWTON’S SECOND LAW

The Law of Acceleration

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WHAT IS ACCELERATION?

Acceleration is a change in velocity over time.

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NEWTON’S SECOND LAW STATES:

  • “Force is equal to the rate of change of momentum. For a constant mass, force equals mass times acceleration.”

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NEWTON’S SECOND LAW

  •  

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https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html

ACCELERATION!

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PRACTICE!

  1. You go to the bowling alley with your friends for some fun. Someone challenges the group to throw the ball as fast as you can. You should get:
  1. The heaviest ball
  2. The lightest ball
  3. Doesn’t matter

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PRACTICE!

  1. You go to the bowling alley with your friends for some fun. Someone challenges the group to throw the ball as fast as you can. You should get:

Answer: The lightest ball! This ball would have the least amount of mass. Because F = ma, you can increase the acceleration by decreasing the mass.

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  1. The heaviest ball
  2. The lightest ball
  3. Doesn’t matter

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PRACTICE!

  1. You go to the bowling alley with your friends for some fun. Someone challenges the group to throw the ball as fast as you can. You go for the 8lb ball (3.6kg). If the acceleration is 10m/s/s, how much force did you apply?
  1. 36N
  2. 0.36N
  3. 2.8N
  4. 80N

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PRACTICE!

  1. You go to the bowling alley with your friends for some fun. Someone challenges the group to throw the ball as fast as you can. You go for the 8lb ball (3.6kg). If the acceleration is 10m/s/s, how much force did you apply?
  1. 36N
  2. 0.36N
  3. 2.8N
  4. 80N

Answer: 36N because F = ma. The mass is 3.6kg and the acceleration is 10m/s/s. The product of 10 and 3.6 is 36, and kg * m/s/s is the same as Newtons.

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NEWTON’S THIRD LAW

The Law of Action-Reaction

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ANY VOLUNTEERS?

You will get to punch stuff…

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NEWTON’S THIRD LAW STATES:

  • “For every action, there is an equal and opposite reaction.”

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ACTION-REACTION

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PRACTICE!

  1. You are driving in a car going 40mph. Your brakes give out and you lose control. You must choose: Should you hit another moving car head on, or should you hit the world’s largest steel cube that is 1,000 feet tall?
  1. The car
  2. The cube
  3. Jump and hope

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PRACTICE!

  1. You are driving in a car going 40mph. Your brakes give out and you lose control. You must choose: Should you hit another car head on that is moving 20mph, or should you hit the world’s largest steel cube that is 1,000 feet tall?
  1. The car
  2. The cube
  3. Jump and hope

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Answer: The safest bet is to probably hit the oncoming car. We know that whatever force you apply will be applied back to you. If you hit an unmoving object, then all of the force will come back to you. It is possible that if you hit the other car, you will only have the force of a 20mph accident.

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LAWS OF MOTION

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INERTIA ACCELERATION ACTION-REACTION