8.3 Newton

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8.3 Newtons Laws of Motion
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First Law of Motion

• An object at rest remains at rest and an object
  in motion keeps moving unless acted on by a
  force

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So the First Law is all about INERTIA

• Resistance to motion
• the more mass in an object, the harder
• it is to get it moving,
• OR to stop it when its already moving.

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• Inertia tendency of an object to resist changes
  in its velocity.
• Inertia tendency of an object to resist
  accelerations.

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You and the car are traveling at same speed.
When the car stops (is stopped by the wall), you
keep going at the same speed until YOU are
acted on by the steering wheel. This is why you
should wear a seat belt!
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Newtons Second Law

• F ma
• Forces cause acceleration

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The unit for force is NEWTON
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Newton gave credit to those who came before him...
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Free Fall and Weight

• As crazy as he may look, our friend does not wish
  to continue gravitational acceleration until he
  hits the ground. He will soon make an effort to
  slow his descent by pulling the ripcord on his
  parachute. We hope.

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Free Fall

• All falling objects (disregarding the effects of
  air resistance) fall at the same rate.
• All falling objects accelerate at the same rate.
  (9.8 m/s2)
• Why?

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INERTIA!

• Sure, gravity is pulling downward.
• But the object is resisting.
• The more mass, the greater the pull downward.
• BUT, the more mass, the greater the resistance.
• So everything ends up coming down at the same
  rate.

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WEIGHT

• Measure of the force of gravity.
• Weight mass X free-fall acceleration
• weight mass X 9.8 m/s2
• w mg
• unit is NEWTON

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Terminal Velocity

• Remember, air has mass.
• So when you are falling, there are real molecules
  underneath you, that you cant see. They help to
  hold you up. Unfortunately, gravity wins. But
  there is a limit to how much you can speed up
  (accelerate) because of the air underneath you
  as you fall. When the pushing up by the air, and
  the pulling down by gravity are equal,
  acceleration (speeding up) stops, and you keep
  falling, but you dont fall any faster.

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• Sky divers reach terminal velocity at about 320
  km /h (200 mi/h)

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Newtons Third Law

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

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Action Reaction Pairs foot presses on ice,
you move in opposite direction.
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Swimmer pushes against the wall, and the wall
pushes back, so she moves away from the wall!