Work & Power
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Slide 1 - Work & Power
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.
- 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.
Slide 3 - Calculating Work
- Work = force x distance
- 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).
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.
Slide 5 - Calculating Power
- You do 10 J of work in 2 seconds:
- The units of power are watts (W).
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
Slide 8 - Machine Example
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.
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.
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?