http://www.ck12.org Chapter 4. Motion and Forces
4.38 Power
- Define power, and relate it to work and time.
- Identify the SI unit for power.
- Show how to calculate power from work and time.
- Describe the unit called the horsepower.
Did you ever sweep a floor with a broom, like the woman in the picture on the left? It can take a lot of effort to do
the job. But if you use an electric vacuum cleaner, like the woman in the picture on the right, you can do the same
work more easily and quickly. That’s because the vacuum cleaner provides more power.
What Is Power?
Poweris a measure of the amount of work that can be done in a given amount of time. Power can be represented by
the equation:
Power=WorkTime
In this equation, work is measured in joules (J) and time is measured in seconds (s), so power is expressed in joules
per second (J/s). This is the SI unit for power, also known as thewatt (W). A watt equals 1 joule of work per second.
You’re probably already familiar with watts. Light bulbs and small appliances such as microwave ovens are labeled
with the watts of power they provide. For example, the package of light bulbs in theFigure4.73 is labeled “14
watts.”
Q: Assume you have two light bulbs of the same type, such as two compact fluorescent light bulbs like the one
pictured in theFigure4.73. If one light bulb is a 25-watt bulb and the other is a 60-watt bulb, which bulb produces
brighter light?
A: The 60-watt bulb is more powerful, so it produces brighter light.