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14.1 Work and Power What is Work? Work is the product of force and distance. Work is done when a force acts on an object in the direction the object moves. Work Requires Motion For a force to do work on an object, some of the force must act in the same direction as the object moves. If there is no movement, no work is done. Work Depends on Direction Any part of a force that does not act in the direction of motion does no work on an object. Calculating Work SI Units of Work When using SI units in the work formula, the force is in newtons, and distance is in meters. The product of force and distance results in the units of newtonmeters, also know as joules. Using the Work Formula Work = Force x Distance Work = 1600 N x 2.0 m Work = 3200 N*m = 3200 J What is Power? Power is the rate of doing work Doing work at a faster rate requires more power. To increase power, you can increase the amount of work don in a given time, or you can do a given amount of work in less time. You know what this needs: More Power! Calculating Power SI Units of Power When using SI units in the power formula, work is in joule (J) and time is in seconds (s). The SI unit of power is the watt (W), which is equal to one joule per second. Watt (W) A 40 watt light bulb requires 40 joules each second that it is lit. 40 watts of power is also approximately equal to lifting your textbook a height of 1 meter in .5 seconds. Using the Power Formula Power = Work = Force x Distance Time Time Power = 72 N x 1.0 m 2.0 s = 36 J/s = 36 W Horsepower One horsepower (hp) is equal to about 746 watts. SI Units Time Seconds (s) Distance Meters (m) Mass Kilogram (kg) Velocity/Speed m/s Acceleration m/s2 Force Newtons (N) Work Joules (J) Power Watts (W)