Mechanical Advantage and Efficiency

4.2 & 4.3

Mechanical Advantage Mechanical Advantage is the number

of times a machine multiplies an effort (input) force.

Generally, this follows the form MA=Fo/Fi where Fo is output force

and Fi is input force Notice that the forces cancel out. MA

has no unit as it is a multiplying factor.

Using machines to do work Machines do not create energy, they

only make it easier to do work through an exchange of distance for force.

Basically, a machine can increase force over a small distance by having an input of a smaller force over a greater distance.

(input) f x D = F x d (output)

Ideal calculations In a perfect world, work in would equal

work out and follow the following equation

di x Fi = do x Fo

This formula can be used to get an estimate of the exchange in forces or distance. Actual measurements would show a decreased output as friction and outside forces are not considered.

Simple Machines Simple machines reduce the force

required to complete work.

We will now examine (notes from whiteboard) how different types of simple machines increase mechanical advantage.

Efficiency Efficiency is the measure of the

amount of useful work is performed by the output of a machine.

Energy is lost in any machine due to friction, heat and other energy robbers.

It is calculated by this formulaEfficiency = Wo/Wi x 100%