14 2 Work and Machines Do Work Ais

14. 2 Work and Machines Do Work • A_______is a device that changes a force. • Machines make work________to do. – They change the size of a force needed, the direction of a force, or the distance over which a force acts. Each complete rotation of a jack handle applies a small force over a large distance. • A small force exerted over a large distance becomes a large force exerted over a short distance. • Each rotation lifts the car only a very short distance.

14. 2 Work and Machines Do Work Increasing ________ • A rower pulls an oar through a small distance. –The end of the oar in the water moves through a large distance. –The increased travel of the oar through the water requires the rower to exert a greater force. • Machines that decrease the distance through which a force is exerted increase the force required.

14. 2 Work and Machines Do Work _________Direction • Pulling back on the handle of the oar causes its other end to move in the opposite direction. • Machines can change the amount of force and the distance the force acts through as well as the direction of the force.

14. 2 Work and Machines Work Input and Work Output Due to friction, work done by a machine is _______ less than the work done on the machine. Work Input to a Machine • Force exerted on a machine: _______force. • Distance the input force acts through: input ________. • Work input = Input force x Input distance

14. 2 Work and Machines –The oars of the boat act as machines that increase the distance over which the force acts –Input force is the force exerted on the handle, input distance is the distance the handle moves, and work input is the work done to move the handle. Boat moves in this direction. Input force Input distance Output force Output distance

14. 2 Work and Machines Work Input and Work Output of a Machine • Force exerted by a machine: output______ • Distance the output force acts through: _____ distance • Work output = Output force X Output distance

14. 2 Work and Machines • Output work results from the oars pushing against the water so that the water pushes back against the oars. • Output work is less than the input work because of friction. • All machines use some input work to overcome friction. Boat moves in this direction. Input force Input distance Output force Output distance

14. 2 Work and Machines Work Input and Work Output The only way to increase the work output is to increase the amount of work you put into the machine. You cannot get more work out of a machine than you _____!