E12
Work, Energy, Power

Work, Energy and Power

Work is force over a distance.

Energy is the capacity to do work.  If work is done on a body, and it is not dissipated in friction, then it is stored in that body either as potential or kinetic energy.  We showed that a spring has potential energy=½·k·x².  A mass has kinetic energy=½·m·v², and if it moves in a gravitational field it has potential energy=m·g·x.  Energy can be dissipated (as heat) in friction elements.

Energy

Spring  
Mass  
Friction

Power is the rate of energy change (the derivative of energy with respect to time).  We showed that for masses, springs, and friction elements,  that power is equal to force time velocity.  Power applied to a spring or mass is stored as energy; potential energy in the position of a spring and kinetic energy in the velocity of a mass.  Power applied to a friction element is dissipated as heat.

Power=force·velocity

Power dissipated by viscouse friction=½·b·v²