<p> Review of Work and Energy</p><p>Work is the process that changes energy from one form to another or one place to another. For work to be done, a force must act on an object, and the position of the object must change. The force must be responsible for the transfer of energy. for constant forces: W = Force · displacement W = (F) (r) cos  for variable forces: W = ∫ F(r) · dr for any force: W = the area “under” a Force vs position graph</p><p>Mechanical energy consists of kinetic energy (dependent on mass and speed), elastic potential energy (dependent on the spring constant and amount of deformation) and gravitational potential energy (dependent on weight and height).</p><p>K = ½ m v2 2 Us = ½ kx Ug = mgh F = -dU/dx Mechanical energy of an object is changed if work is done on the object by a non–conservative force. Two conservative forces: the gravitational force, and the restoring (spring) force.</p><p>Fs = -kx Fg = mg</p><p>The work done by non-conservative (or external) forces can be calculated in the way one calculates the work done by any individual force, as shown above, or using the work – energy equation:</p><p>U + K + WNC = U + K</p><p>When kinetic friction or drag does work, mechanical energy is converted into heat energy. When any other non-conservative force does work, energy is converted from some form into mechanical energy if WNC is positive, and energy is converted from mechanical to some other form (usually heat) if WNC is negative. </p><p>Power is defined as the rate at which work is done.</p><p>P = W÷t P = dW / dt P = F v</p>