Simple Machines

Simple Machine - a device that changes

the size or direction of a force being used to

do work.

WORK: You are doing work when you use a force to cause motion in the same direction.

To measure the amount of work , multiply the force times the distance the object moved.

Work = F x D (work= force x distance the

object moved)

WF*D

Force (or weight) is measured in newtons

Distance is measured in meters.

The unit of measure for work = Joule (J)

We can measure how much the force is changed by calculating mechanical

advantage.

The force applied to do work is called the effort force (input).

The force that opposes motion is called the

resistance force (output).

Actual mechanical advantage is the

number of times a machine multiplies an

effort force.

Ideal mechanical advantage does not consider friction.

There are six types of simple machines

• Lever

• Incline plane

• Wedge

• Screw

• Pulley

• Wheel and axle

LEVER: The lever is a simple machine made with a bar free

to move about a fixed point called a fulcrum.

There are three types of levers.

•First class

•Second class

•Third class

A first class lever is like a teeter-totter or seesaw.

First class lever.

Resistance Force

FulcrumEffort Force

A second class lever is like a wheelbarrow. The long handles of a wheel

barrow are really the long arms of a lever.

Second Class Lever

Fulcrum

Resistance Force

Effort Force

A third class lever is like a fishing pole. When the pole is given a tug, one

end stays still but the other end flips in the air

catching the fish.

Third class lever

Fulcrum

EffortResistance

The mechanical advantage of a lever is calculated by dividing the Resistance

force by the Effort Force. MA = RF/EF

INCLINED PLANE: An inclined plane is a simple

machine with no moving parts. It is simply a straight slanted

surface. (Ex. a ramp.)

30

10

A box with mass of 30 Newtons is lifted 10 meters to the top of a loading dock.

18 20

With the incline plane the effort distance is increased, and the effort force is decreased.

1030

The effort force can be further reduced by increasing the length of the effort distance.

The mechanical advantage of an inclined plane is

calculated by dividing the Resistance force by the

Effort force.MA = RF/EF

The ideal mechanical advantage of an inclined

plane is calculated by dividing the Effort

distance by the Resistance distance.

IMA = ED/RD

PULLEY: A pulley is a simple machine made with a rope, belt

or chain wrapped around a grooved wheel. A pulley works

two ways. It can change the direction of a force or it can change the amount of force.

A fixed pulley changes the direction of the applied force. (Ex. Raising the flag). A movable pulley is

attached to the object you are moving.

The mechanical advantage of a pulley is calculated by dividing the Resistance force by

the Effort force.MA=RF/EF

Power is the amount of work done in a

period of time. Power is calculated by the following formula:

P=W/t

Efficiency is the ratio of the work calculated by (output work/input

work) * 100.

Compound machine - a machine that is a

combination of two or more simple machines.