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Forces

Unit 3: Dynamics of Motion

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Forces

A force is a push or a pull or an action that has the ability to change motion

  • Forces can increase or decrease the speed of a moving object

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Newtons

Although we use pounds all the time in our everyday life, scientists prefer to measure forces in newtons

  • The newton (N) is a metric unit of force

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Newtons (cont.)

  • The newton (N) is a smaller unit of force than the pound (lb)
  • One pound of force = 4.448 newtons

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gravity

  • The force of gravity on an object is called weight
  • At Earth’s surface, gravity exerts a force of �9.8 N on every kilogram of mass

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Friction

  • Friction is a force that resists the motion of objects or surfaces
  • Many kinds of friction exist

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Static Friction

  • Static friction acts on objects that are not moving.
  • Ex: Your cell phone resting on a desk

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Sliding Friction

  • Sliding friction opposes the direction of motion of an object as it slides over a surface
  • Ex: Pushing your phone across the surface of the desk

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Rolling Friction

  • Rolling friction is the force that acts on rolling objects
  • Ex: skateboarding, riding a bike

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Fluid Friction

  • Fluid friction opposes the motion of objects going through fluid
    • Ex: surfing
  • Water and air are�types of fluids

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