Name _______________ Class ____ Date ______________ Chapter 8 Energy Summary The Big Idea! Energy can change from one form to another without a net loss or gain. 8.1 Work Work is done when a force acts on an object and the object moves in the direction of the force. Work is the product of the force on an object and the distance through which the object is moved. In the simplest case1 when the force is constant; the motion takes place in a straight line in the direction of the force: work = force x distance. In equation form, W = Fd. Work generally falls into two categories: work done against another force and work done to change the speed of an object. In both categories 1 work involves a transfer of energy between something and its surroundings. The unit of work is the newton-meter (N·m); also called the joule. One joule (J) of work is done when a force of 1 N is exerted over a distance of 1 m. 8.2 Power Power equals the amount of work done divided by the time interval during which the work is done. Power is the rate at which work is done: A high-power engine does work rapidly. If an engine has twice the power of another engine1 this means that it can do twice the work in the same amount of time or the same amount of work in half the time. The unit of power is the joule per second1 which is also known as the watt. One watt (W) of power is expended when one joule of work is done in one second. In the United States1 we customarily rate engines in units of horsepower and electricity in kilowatts1 but either may be used. One horsepower (hp) is the same as 0.75 kW. 8.3 Mechanical Energy The two forms of mechanical energy are kinetic energy and potential energy. The property of an object or system that enables it to do work is energy. Like work1 energy is measured in joules. Mechanical energy is the energy due to the position of something or the movement of something.
Name _______________ Class ____ Date ______________ Chapter 8 Energy Summary The Big Idea! Energy can change from one form to another without a net loss or gain. 8.1 Work Work is done when a force acts on an object and the object moves in the direction of the force. Work is the product of the force on an object and the distance through which the object is moved. In the simplest case1 when the force is constant; the motion takes place in a straight line in the direction of the force: work = force x distance. In equation form, W = Fd. Work generally falls into two categories: work done against another force and work done to change the speed of an object. In both categories 1 work involves a transfer of energy between something and its surroundings. The unit of work is the newton-meter (N·m); also called the joule. One joule (J) of work is done when a force of 1 N is exerted over a distance of 1 m. 8.2 Power Power equals the amount of work done divided by the time interval during which the work is done. Power is the rate at which work is done: A high-power engine does work rapidly. If an engine has twice the power of another engine1 this means that it can do twice the work in the same amount of time or the same amount of work in half the time. The unit of power is the joule per second1 which is also known as the watt. One watt (W) of power is expended when one joule of work is done in one second. In the United States1 we customarily rate engines in units of horsepower and electricity in kilowatts1 but either may be used. One horsepower (hp) is the same as 0.75 kW. 8.3 Mechanical Energy The two forms of mechanical energy are kinetic energy and potential energy. The property of an object or system that enables it to do work is energy. Like work1 energy is measured in joules. Mechanical energy is the energy due to the position of something or the movement of something.
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