Simple Machines Machines Lever Inclined plane Pulley Screw

Simple Machines

Machines • • • Lever Inclined plane Pulley Screw Wedge Wheel & axle

Machines • Device to multiply force or change its direction • Can’t increase work done • Work put into machine must be at least as great as the work output of machine

Machines • Since work is force times distance, input force can be decreased by increasing input distance: force is “multiplied” • Work is made easier because less force is needed • Sometimes output distance is increased by increasing input force: distance is multiplied

Efficiency • Work output divided by work input (x 100 for %) • A measure of losses due to friction • Efficiency is always less then 100%

Mechanical Advantage • A measure of how much the effect of the force is increased • Actual M. A. is ratio of output force to input force • Theoretical M. A. can be found from the design of the machine

Mechanical Advantage • For lever, theoretical MA is input distance / output distance • For inclined plane it is plane length / height • For pulley system it equals the number of cords supporting the weight being lifted

Summary • Machines help us do work by using less force over greater distance • Mechanical Advantage = output force / input force • Efficiency = work out / work in