Chapter 6 - Forces In Motion

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Chapter 6 - Forces In Motion

• Section 2 Newtons Laws of Motion
• pp. 158 - 165

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TERMS TO LEARN

• Inertia the tendency of all objects to resist
  any change in motion
• Momentum a property of a moving object that
  depends on the objects mass and velocity.

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NEWTONS THREE LAWS OF MOTION

• In his book, Principia, Newton described the
  three laws of motion.
• He did not discover all three laws, he explained
  them in a way that many people could understand

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NEWTONS FIRST LAW OF MOTION

• This is also known as the Law of Inertia
• It says An object in motion will remain in
  motion at a constant speed and in the same
  direction unless acted on by an unbalanced force.
• An object at rest will remain at rest unless
  acted upon by an unbalanced force.

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NEWTONS FIRST LAW OF MOTION

• In other words
• Unless you apply a force, things tend to keep on
  doing what they were doing in the first place.
• Objects at rest (not moving) will not begin
  moving unless a push or pull is exerted on them.

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NEWTONS FIRST LAW OF MOTION
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NEWTONS FIRST LAW OF MOTION

• An object moving at a certain velocity will
  continue to move forever at that same speed and
  in the same direction unless an unbalanced force
  acts on it.
• Inertia is related to mass. Mass is a measure of
  inertia.

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NEWTONS FIRST LAW OF MOTION

• An object with a small mass has less inertia than
  an object with a large mass.
• For example
• A tractor trailer has more mass than a motorcycle

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NEWTONS FIRST LAW OF MOTION

• How do ABS (automatic brake systems) work in
  cars?
• The system is controlled by a computer that
  prevents skidding by sensing when the wheels are
  about to lock.

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ABS BRAKES EXPLAINED

• The computer releases and reapplies the brakes up
  to 25 times a second. Instead of skidding out of
  control, the car slows down and stops safely.

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NEWTONS SECOND LAW OF MOTION

• The acceleration of an object depends on the mass
  of the object and the amount of force applied to
  it.
• Equation F ma
• Force mass times acceleration

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NEWTONS SECOND LAW OF MOTION

• Acceleration depends on force. Acceleration and
  force are directly proportional. This means as
  force increases acceleration also increases and
  vice versa.

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NEWTONS SECOND LAW OF MOTION

• Acceleration also depends on mass. Acceleration
  and mass are inversely proportional. This means
  as mass increases, acceleration decreases and
  vice versa.
• Remember that mass is also a measure of an
  objects inertia.
• Complete Math Focus on p. 162 of text.

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NEWTONS SECOND LAW OF MOTION

• In other words
• Force causes an object to accelerate, while the
  objects mass resists the acceleration.
• The larger the object (the more mass it has), the
  harder it is to accelerate.

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NEWTONS THIRD LAW OF MOTION

• Whenever one object exerts a force on a second
  object, the second object exerts a force that is
  equal in size and opposite in direction on the
  first

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NEWTONS THIRD LAW OF MOTION

• In other words
• For every action there is an equal and opposite
  reaction.

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NEWTONS THIRD LAW OF MOTION

• All forces act in pairs called action-reaction
  force pairs
• If a force is exerted, another force occurs that
  is equal in size and opposite in direction to the
  first.
• ACTION-REACTION FORCE PAIRS DO NOT ACT ON THE
  SAME OBJECT! See Figure 7 Figure 8 on p. 164.

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MOMENTUM

• Momentum is a property of a moving object that
  depends on its mass and velocity.
• The more momentum an object has, the harder it is
  to stop the object or change its direction.

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MOMENTUM

• Equation for Momentum
• p mv
• Where p momentum, m mass and v velocity