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