Notes: MachinesCW: Man & MachinesH: Simple Machines

Machines

April 15, 2009

Objectives

1. Explain how a machine makes work easier

2. Calculate mechanical advantage3. Describe an ideal machine 4. Explain why machines are not

100% efficient

History of Work

Simple Machines

Machines make work easier.

W = F x D

The two most common resistive forces are friction and gravity

Machines

Simple Machines

a device that does work with only one a device that does work with only one movementmovement

Types of Simple Machines

1. inclined plane2. wedge 3. lever4. wheel & axle5. screw6. pulley

These make work

easier !

Machines make work easier by changing

1. the amount of force you exert

2. the distance over which you exert your force

3. the direction over which you exert your force

when using a machine to do work

Effort (Input) Force (FE) –the force you apply to the machine

Resistance (Output) Force (FR) –the force that the machine applies

2 forces involved

Work In (Win) – The work done on the machine (energy put into the machine)

Work Out (Wout) – The work done by the machine (energy put out by the machine)

2 types of work involved

Mechanical Advantage

The number of times a machine increases a force exerted on it

MA = output force / input force

Machines make work easier by changing

1. the amount of force you exertthe MA is greater than 1

2. the distance over which you exert your force the MA is less than 1

3. the direction over which you exert your force

the MA is equal to 1

Efficiency

Compares the output work to the input work.

Efficiency = Wout x 100%

Win

The higher the percent, the more efficient the machine.

one in which there is no friction, no energy is lost so Win=Wout

In reality, work out will always be less than work in because energy is lost through friction

Ideal machineIdeal machine