Work and Machines How machines make our lives easier

Machines A machine is a device that changes a force Machines make work easier to do Machines change the size of the force needed, the direction of the force, or the distance over which a force acts Example a lug wrench and jack allow a person to change a car tire

Increasing Force A small force exerted over a large distance becomes a large force over a short distance Example a jack lifts a car a small bit at a time but the distance the jack moves is large

Increasing Force If a machine increases the distance traveled then it lessens the force required Example moving books one at a time takes less force but requires more distance than moving the whole stack at once

Increasing Distance A machine may decrease the distance the force moves but increases the force required Example is a crew team rowing a boat Each oar pull is short but the distance the boat moves is long, the distance is shorter and the force needs to be greater

Changing Direction Machines can also change the direction of the force For example, when pulling on an oar, one end of the oar goes in the opposite direction This has changed the direction of the force

Work Input The force you input on a machine is called input force The distance the input force acts through is known as the input distance The work done by the input force acting through the input distance is called the work input The work input equals the input force times the input distance (think: work = force x distance)

Work Output The force exerted by a machine is the output force The distance the output force is exerted is the output distance The work output is the output force times the output distance

Work Input and Work Output Output and input work are nearly equal The output work will be less All machines need to use input work to overcome friction