# Work & Power

Created 2 years ago

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2. ### 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. ### 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. ### 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. ### Slide 5 - Calculating Power

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

8. ### 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. ### 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. ### 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?