Machines, Mechanical Advantage and Efficiency

What is a Machine?A machine makes work

easier and more effective.

A machine never changes the amount of work needed to do a job.

HOW IS THAT?

Multiply ForceInput Force

Output Force

Input Work = Output Work

W= 1N x 4m W= 4N x 1m

4 J 4 J

Multiply DistanceInput Force

Output Force

Input Work = Output Work

W= 4N x 1m W= 1N x 4m

4 J 4 J

Change Direction

Output Force

Input Force

Input Work = Output Work

W= 2N x 2m W= 2N x 2m

4 J 4 J

A machine makes work easier by

Changing the amount of force you exert

A machine makes work easier by

Changing the distance over which you exert your force

A machine makes work easier by

Changing the direction in which you exert your force.

A machine can make work easier by1. Multiplying force2. Multiplying distance3. Changing Direction

Input Force“Effort Force”

The force you exert on the machine

Output Force“Resistance Force”

The force exerted by the machine

Mechanical Advantage

The number of times a force exerted on a machine is multiplied by the machine.

Mechanical Advantage

If a machine has a mechanical advantage of 5, that means it multiplies the force by 5 times

(5 times easier)

Mechanical Advantage

ActualMechanicalAdvantage=

Output force

Input force

Mechanical Advantage of Multiplying Force

The mechanical Advantage is greater than 1

The machine multiplies your force

The output force is greater than the input force.

Efficiency of Machines

The efficiency of a machine compares the output work to the input work.

Part of the work done by a machine is wasted on friction

Calculating Efficiency

Efficiency = Output Work Input Work

X 100%

Actual Mechanical Advantage

The mechanical advantage that a machine provides in a real situation.

Depends on the efficiency of the machine

Ideal Mechanical Advantage

The mechanical advantage of a machine without friction.

The more efficient a machine is, the closer the actual mechanical advantage is to the ideal mechanical advantage.

Machine’s Efficiency

Machine (a) 95 % efficient (AMA) 5 % lost due to

friction Machine (b) 75 % efficient (AMA) 25 % lost due to

friction Machine (c) 100 % efficient (IMA) perfect machine no

friction Machine (d) 25 % efficient (AMA) 75 % lost due to

friction What machine will run the hottest? How can you increase the machine’s

efficiency