Work & Power


Work & Power

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  1. Work & Power

    Slide 1 - Work & Power

  2. Work

    Slide 2 - Work

    • When you apply a force to an object and the object moves in the same direction as that force, you are doing work.
    • Examples.
    • When you push a box across a floor, that’s work.
    • When you push on a wall, but it doesn’t budge. That is not work.
  3. Calculating Work

    Slide 3 - Calculating Work

    • Work = force x distance
    • Example:
    • You apply a force of 12 N to a box and move it 8 m across the floor. How much work was done?
    • The units of work are the “Newton-meter” (N·m), which is also called a Joule (J).
  4. Power

    Slide 4 - Power

    • Power is the rate at which work is done.
    • If an object has more power than another it either:
    • Gets more work done in the same amount of time
    • Gets the same work done in a shorter amount of time
    • Example: you and a friend are hiking up a hill carrying backpacks that make your mass identical. If you reach the top before your friend, you hiked with more power.
  5. Calculating Power

    Slide 5 - Calculating Power

    • You do 10 J of work in 2 seconds:
    • The units of power are watts (W).
  6. Machines

    Slide 7 - Machines

    • Machines are devices that makes work easier in at least one of these three ways:
    • 1. Change the amount of force you exert
    • 2. Change the distance over which the force is exerted
    • 3. Change the direction in which you exert the force
  7. Machine Example

    Slide 8 - Machine Example

  8. Input & Output Force

    Slide 10 - Input & Output Force

    • The force you exert on machine is called the input force.
    • The force the machine exerts is called the output force.
    • Since machines make work easier, the output force can never be less than your input force unless you change the distance or direction.
  9. Mechanical Advantage

    Slide 11 - Mechanical Advantage

    • The ratio of the output force to the input force is called the mechanical advantage.
    • Mechanical advantage is a ratio so it does not have units.
  10. Mechanical Advantage Example

    Slide 12 - Mechanical Advantage Example

    • A pulley system allows you to apply 10N of force and lift a box with a force of 15N. What is the mechanical advantage of the pulley system?