In words: Power is the amount of work done divided by the time it takes to do that work. Scientists define power as the rate at which work is done, or the rate at which energy is expended. A power hitter in baseball swings the bat faster, converting the chemical energy in his muscles to kinetic energy more quickly than most other players. If you run up a flight of stairs, your muscles need to generate more power than they would if you walked up the same flight, even though you expend the same amount of energy in either case. In order to complete a physical task quickly, you must generate more power than if you do the same task slowly. Power provides a measure of both the amount of work done (or, equivalently, the amount of energy expended) and the time it takes to do that work. When a system runs out of energy, it simply can’t do any more work. The amount of a system’s energy, which can be recorded in joules or foot-pounds (the same units used for work), is a measure of how much work the system might do. If a system is capable of exerting a force over a distance, then that system possesses energy. Solution: Then, from the equation for work,Įnergy is defined as the ability to do work. We know that to lift a 20-kg mass against the acceleration of gravity (9.8 m/s 2) requires a force given by Reasoning: We must first calculate the force exerted by a 20-kg mass before we can determine work. How much work do you do when you carry a 20-kg television set up a flight of stairs (about 4 meters)? In the English system of units, where force is measured in pounds, work is measured in a unit called the foot-pound (usually abbreviated ft-lb). One joule is defined as the amount of work done when a force of one newton is exerted through a distance of one meter.ġ joule of work = 1 N of force x 1 m of distance This unit is given the special name “joule,” after the English scientist James Prescott Joule (1818–1889), one of the first people to understand the properties of energy. For reference, a newton is roughly equal to the force exerted on your hand by a baseball. In the metric system of units, where force is measured in newtons (abbreviated N), work is measured in newton-meters (N-m).
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![one meter in feet one meter in feet](https://converter.ninja/images/1_m_in_ft.jpg)
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In practical terms, even a small force can do a lot of work if it is exerted over a long distance.Īs you might expect from this equation, units of work are equal to a force unit times a distance unit. Where a joule is the unit of work, as defined in the following paragraph.
![one meter in feet one meter in feet](https://ph-static.z-dn.net/files/d25/b5e28902e2c6c5ef33196c084f176531.jpg)
In equation form: work (joules) = force (newtons) x distance (meters), In words: Work is equal to the force that is exerted times the distance over which it is exerted. Physicists provide an exact mathematical definition of their notion of work. Even though you have exerted a considerable force, the distance over which you exerted it is negligible. On the other hand, a physicist would say that you haven’t done any work if you spend an hour in a futile effort to move a large boulder, no matter how tired you get. From a physicist’s point of view, if you accidentally drive into a tree and smash your fender, work has been done because a force deformed the car’s metal a measurable distance. This definition of work differs considerably from everyday usage. Your muscles applied a force equal to the weight of the book over a distance of a foot. Scientists say that work is done whenever a force is exerted over a distance. (From The Sciences, 6th ed., by Trefil and Hazen)