How is power measured in physics

Horsepower is often used to describe the power delivered by a machine. Horsepower is a unit of power in the British system of measurement. It is the power required to lift pounds by one foot in one second and is about watts. The watt is often seen in relation to light bulbs. In this power rating, it is the rate at which the bulb converts electrical energy into light and heat.

A bulb with a higher wattage will use more electricity per unit of time. If a bulb has a power rating of 50 watts, it will produce 50 joules per second. In an hour seconds it will produce , joules. When you walk a mile, your motive force is displacing your body, which is measured as the work is done. When you run the same mile, you are doing the same amount of work but in less time.

The runner has a higher power rating than the walker, putting out more watts. A car with 80 horsepower can produce faster acceleration than a car with 40 horsepower. In the end, both cars are going 60 miles per hour, but the hp engine can reach that speed faster. In the race between the tortoise and the hare, the hare had more power and accelerated faster, but the tortoise did the same work and covered the same distance in a much longer time.

When work is done on an object, energy is transferred. The rate at which this energy is transferred is called power. So the more powerful a device is, the more energy it will transfer each second. The equation used to calculate the power is:. This is when:. So the energy consumed over a time t is. This unit is convenient because electrical power consumption at the kilowatt level for hours at a time is typical.

What is the cost of running a 0. The cost of using the computer in this example is neither exorbitant nor negligible. It is clear that the cost is a combination of power and time. When both are high, such as for an air conditioner in the summer, the cost is high.

The motivation to save energy has become more compelling with its ever-increasing price. Armed with the knowledge that energy consumed is the product of power and time, you can estimate costs for yourself and make the necessary value judgments about where to save energy.

Either power or time must be reduced. It is most cost-effective to limit the use of high-power devices that normally operate for long periods of time, such as water heaters and air conditioners. This would not include relatively high power devices like toasters, because they are on only a few minutes per day.

It would also not include electric clocks, in spite of their hour-per-day usage, because they are very low power devices. It is sometimes possible to use devices that have greater efficiencies—that is, devices that consume less power to accomplish the same task.

One example is the compact fluorescent light bulb, which produces over four times more light per watt of power consumed than its incandescent cousin.

Modern civilization depends on energy, but current levels of energy consumption and production are not sustainable. The likelihood of a link between global warming and fossil fuel use with its concomitant production of carbon dioxide , has made reduction in energy use as well as a shift to non-fossil fuels of the utmost importance.

Even though energy in an isolated system is a conserved quantity, the final result of most energy transformations is waste heat transfer to the environment, which is no longer useful for doing work. Skip to main content.

Work, Energy, and Energy Resources. If the tired squirrel does all this work in 2 seconds, then determine its power. The tired squirrel does 0. The power rating of this squirrel is found by. When doing a chin-up , a physics student lifts her What is the power delivered by the student's biceps?

The work done to lift her body is. Your household's monthly electric bill is often expressed in kilowatt-hours.

One kilowatt-hour is the amount of energy delivered by the flow of l kilowatt of electricity for one hour. Use conversion factors to show how many joules of energy you get when you buy 1 kilowatt-hour of electricity.

First, convert 1 kW-hr to Watt-hours. Then convert Watt-hours to 3. Since a Watt-second is equivalent to a Joule, you have found your answer. An escalator is used to move 20 passengers every minute from the first floor of a department store to the second.

The second floor is located 5. The average passenger's mass is Determine the power requirement of the escalator in order to move this number of passengers in this amount of time.

A good strategy would involve determining the work required to elevate one average passenger. Then multiply this value by 20 to determine the total work for elevating 20 passengers.

Finally, the power can be determined by dividing this total work value by the time required to do the work. The solution goes as follows:.