Power tells you the rate at which you expend/use energy. A watt (W) is 1 joule/second (J/s), where a joule is a unit of energy -- and a joule is not very large. So your 100 W light bulb uses 100 J of energy every second. To show you that that is not a lot, consider the kilowatthour (kWh) the typical unit of energy on US electricity bills. In my area (Omaha) 1 kWh of energy costs about $0.10. But 1 kWh = 3.6 Million(!) joules of energy!! If you used your 100 W light bulb for 10 hours, then you have used 1 kWh of energy.

Another way of looking at it is the conversion between a joule and a dietary calorie (Cal). 1 Cal = 4186 joules. If you burn 1 Cal/s, this is a power output of 4186 W. Just think about that the next time you stop for pie on your bike ride!

Glenn in Omaha