2. POWER The rate at which work is done The rate at which work is done The amount of work done in a unit of time The amount of work done in a unit of time

3. POWER Calculating power Calculating power Power = work/time Power = work/time Since work = force x distance…. Since work = force x distance…. Power = force X distance Power = force X distance time time

4. POWER When work is measured in Joules (J) and time in seconds (s); Power is joule per second J/s When work is measured in Joules (J) and time in seconds (s); Power is joule per second J/s J/s is also known as the Watt (W) J/s is also known as the Watt (W)

5. POWER 1 watt (W) = 1 J/s 1 watt (W) = 1 J/s A watt is a relatively small unit of power. A watt is a relatively small unit of power. Power in larger units is measured in kilowatts (kW) Power in larger units is measured in kilowatts (kW) 1 kW = 1,000 W 1 kW = 1,000 W

6. POWER Solve the following: Solve the following: A crane lifts an 8,000-N beam 75 m to the top of a building in 30 s. How much power does the crane use? A crane lifts an 8,000-N beam 75 m to the top of a building in 30 s. How much power does the crane use?

7. POWER The force needed to lift the beam = its weight The force needed to lift the beam = its weight Distance & time are given Distance & time are given Power = 8,000 N X 75 m 30s 30s

8. POWER Try this: Try this: A motor exerts a force of 10,000 N to lift an elevator 6 m in 5s. What is the power produced by the motor? A motor exerts a force of 10,000 N to lift an elevator 6 m in 5s. What is the power produced by the motor?

9. POWER Try this: Try this: A tow truck exerts a force of 9,000 N to pull a car out of a ditch. It moves the car a distance of 6 m in 25s. What is the power of the tow truck? A tow truck exerts a force of 9,000 N to pull a car out of a ditch. It moves the car a distance of 6 m in 25s. What is the power of the tow truck?

10. POWER Power can be defined another way… Power can be defined another way… The rate at which energy is transferred from one object to another or converted from one form to another. The rate at which energy is transferred from one object to another or converted from one form to another.

11. POWER Power is not limited to just when things are moved; can be found whenever energy is being transferred or converted Power is not limited to just when things are moved; can be found whenever energy is being transferred or converted

12. Horsepower 1 horsepower = 746 W 1 horsepower = 746 W Horsepower is NOT an SI unit Horsepower is NOT an SI unit Comparison to the amount of work a horse could do VS a steam engine Comparison to the amount of work a horse could do VS a steam engine