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?
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