Newtons Laws of Motion

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Newtons Laws of Motion

• Mrs. Kay
• Physics 11

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Newtons 1st Law

• An object with no net force acting on it remains
  at rest or moves with a constant velocity in a
  straight line.
• Also called the law of inertia (objects tend to
  keep on doing what they are doing)

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• Means
• An object that is not moving at all will not
  move unless a force (push or pull) acts upon it.
  
• An object that is already moving, will move
  forever if no force acts upon it to slow it down
  (no friction or stopping)

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Examples of Newtons 1st Law

• blood rushes from your head to your feet while
  quickly stopping when riding on a descending
  elevator.
• the head of a hammer can be tightened onto the
  wooden handle by banging the bottom of the handle
  against a hard surface.
• while riding a skateboard , you fly forward off
  the board when hitting a curb or rock or other
  object which abruptly halts the motion of the
  skateboard.
• Other examples?

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Newtons 2nd Law

• Acceleration of a body is directly proportional
  to the net force on it, and inversely
  proportional to its mass.
• Means The larger the force acting on an object,
  the greater the acceleration and the faster it
  will move.

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• Acceleration depends on mass. If you push a small
  ball and a heavy ball with the same force it is
  the small ball that will have the greater
  acceleration.
• F ma or a F
• m
• Units for force

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Newtons 3rd Law

• When one object exerts a force on a second
  object, the second object exerts a force on the
  first that is equal in magnitude, but opposite in
  direction.
• For every action there is an equal but opposite
  reaction

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• Means
• Forces always happen in pairs.
• This book is being pulled down by gravity, and
  pushes upward with an equal amount of force

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• If a small force is exerted, then an equally
  small force will be exerted back.
• - Called action-reaction forces

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Mass and Weight

• Weight
• Gravitational force exerted by a large object
  (usually Earth) on a smaller object (anything on
  Earth)
• Unit Newtons (N)
• Wmg
• It depends upon gravity, therefore may change
  depending on altitude
• Tend not to say negative weight, but say
  downwards.

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• Mass
• the property of a body that causes it to have
  weight in a gravitational field
• It is constant regardless of where it is
  measured.

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Problems

• List 3 different examples of Newtons 1st Law.
• Describe Newtons 3rd Law using the example of me
  kicking a bowling ball. Ouch!
• On pg.92 1-4
• On pg 94 5-8