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ENERGY Notes and Key Concepts Work An object’s motion is related to both force and how the force acts. The quantity force X time = impulse The quantity force X distance = work WORK Two factors are considered when work is done 1. The application of a force 2. The movement of something by that force The work done on an object by an applied force is the product of the force and the distance through which the object moved Work=force x distance W=Fd POWER Power is the rate at which work is done Power=work done/time interval The unit of power is the joule per second, also known as the watt One watt (W) of power is expended when one joule of work is done in one second 1 Kilowatt (kW)= 100 watts 1 megawatt (MW) = one million watts Metric System vs. United States In the metric system, automobiles are rated in kilowatts In the U.S, we rate engines in units of horsepower and electricity in kilowatts One horsepower (hp, is the same as 0.75 kW, so an engine rated at 134 hp is a 100kW engine Mechanical Energy Potential Potential energy is stored and held in readiness (a spring or stretched rubber band) Examples: fossil fuels, electric batteries, and food Gravitational potential energy= weight x height PE=mgh Kinetic Kinetic energy is energy of motion It depends on mass and speed of an object Kinetic energy = ½ mass x speed2