Chapter 3: Forces

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Table of Contents
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Unit 1 Energy and Motion
Chapter 3 Forces
3.1 Newtons Second Law
3.2 Gravity
3.3 The Third Law of Motion
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Newtons Second Law
3.1
Force and Acceleration

• Whats different about throwing a ball
  horizontally as hard as you can and tossing it
  gently?

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Newtons Second Law
3.1
Mass and Acceleration

• If you throw a softball and a baseball as hard as
  you can, why dont they have the same speed?

• The difference is due to their masses.

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Newtons Second Law
3.1
Mass and Acceleration

• Heavy object? less acceleration
• Light object? More Acceleration

• Force, mass, and acceleration are related.

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Newtons Second Law
3.1
Newtons Second Law
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Newtons Second Law
3.1
Calculating Net Force with the Second Law

• Newtons second law also can be used to calculate
  the net force if mass and acceleration are known.

• To do this, the equation for Newtons second law
  must be solved for the net force, F.

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Newtons Second Law
3.1
Calculating Force with the Second Law

• Mass x Acceleration Force
• Force is measured in Newtons

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The Third Law of Motion
3.3
Newtons Third Law

• Newtons third law of motion
• For every action there is an equal and opposite
  reaction

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The Third Law of Motion
3.3
Action and Reaction

• When you jump on a trampoline, for example, you
  exert a downward force on the trampoline.

• Simultaneously, the trampoline exerts an equal
  force upward, sending you high into the air.

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The Third Law of Motion
3.3
Action and Reaction Forces Dont Cancel

• For example, a swimmer acts on the water, the
  reaction of the water pushes the swimmer
  forward.

• Thus, a net force, or unbalanced force, acts on
  the swimmer so a change in his or her motion
  occurs.

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The Third Law of Motion
3.3
Rocket Propulsion

• In a rocket engine, burning fuel produces hot
  gases. The rocket engine exerts a force on these
  gases and causes them to escape out the back of
  the rocket.

• Newtons third law, the gases exert a force on
  the rocket and push it forward.

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End of Chapter Summary File