PowerPower

The Crab Nebula,

supernova remnant

PowerPower

• Like work, we’ve all heard about power

• But what is it?

• Scientists define power as the amount of work done divided by the time it takes to do that work

• Power is work’s rate of change

PowerPower = = Work Work / / TimeTime

Definition #2Definition #2

• As work is related to energy, we can also define power as the rate of energy use

• Power = Change in Energy/Elapsed Time

UnitsUnits

• The units of power are Joules/seconds

• 1J/s = 1 Watt (W)

• So if you lift your 1lb weight 10inches in the air in 1second, your power is 1watt

Power ComparisonsPower Comparisons

• Light Bulb: 100 W• Vacuum Cleaner: 1,500 W• Dodge Ram w/ Hemi: 250,000 W• Space Shuttle: 11,000,000,000 W• Sun: 400,000,000,000,000,000,000,000,000 W

QuestionQuestion

• A machine does 200J of work over a time interval of 20s. What is this machine’s power?

• 10W

How much Energy does a 40W How much Energy does a 40W light bulb consume in 2 light bulb consume in 2

minutes?minutes?

Machine A performs a certain amount of Machine A performs a certain amount of work in time t. Machine B performs twice as work in time t. Machine B performs twice as much work as 1, but takes 4 times as long. much work as 1, but takes 4 times as long. Machine C performs the same amount of Machine C performs the same amount of work as 1, but in ½ the time. Rank the work as 1, but in ½ the time. Rank the

power of each machine in increasing order.power of each machine in increasing order.

• 1. A, B, C 2. C, B, A

• 3. C, A, B 4. B, A, C

• 5. B, C, A

Using a 40N force, a pulley system Using a 40N force, a pulley system pulls a box forward at a constant pulls a box forward at a constant

velocity of 2m/s. What is this pulley velocity of 2m/s. What is this pulley system’s power? system’s power?