# compound machine

## what is a compound machine

A compound machine is a machine that consists of more than one simple machine. Some compound machines consist of just two simple machines. You can read below about two examplesthe wheelbarrow and corkscrew. Other compound machines, such as bicycles, consist of many simple machines. Big compound machines such as cars may consist of hundreds or even thousands of simple machines.

## wheelbarrow

Look at the wheelbarrow in the Figure 1.1. It is used to carry heavy objects. It consists of two simple machines: a lever and a wheel and axle. Effort is applied to the lever by picking up the handles of the wheelbarrow. The lever, in turn, applies upward force to the load. The force is increased by the lever, making the load easier to lift. Effort is applied to the wheel of the wheelbarrow by pushing it over the ground. The rolling wheel turns the axle and increases the force, making it easier to push the load.

## efficiency of compound machines

Friction is a force that opposes motion between any surfaces that are touching. All machines have moving parts and friction, so they have to use some of the work that is applied to them to overcome friction. This makes all machines less than 100 percent efficient. Because compound machines have more moving parts than simple machines, they generally have more friction to overcome. As a result, compound machines tend to have lower efficiency than simple machines. When a compound machine consists of many simple machines, friction can become a serious problem, and it may produce a lot of heat. Lubricants such as oil or grease may be used to coat the moving parts of a machine so they slide over each other more easily. This is how friction is reduced in a car engine.

## corkscrew

The corkscrew in the Figure 1.2 is also a compound machine. It is used to pierce a cork and pull it out of the neck of a bottle. It consists of a screw and two levers. Turning the handle on top twists the screw down into the center of the cork. Then, pushing down on the two levers causes the screw to pull upward, bringing the cork with it. The levers increase the force and change its direction.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

some compound machines consist of thousands of simple machines.

``````-->  a. true

b. false
``````

when you use a wheelbarrow, you apply effort to the

``````a) wheel.

b) axle.

c) lever.

-->  d) two of the above
``````

a corkscrew consists of

``````a) two levers.

b) a screw.

c) a wheel and axle.

-->  d) two of the above
``````

all machines must overcome friction.

``````-->  a. true

b. false
``````

no machine is 100 percent efficient.

``````-->  a. true

b. false
``````

## diagram questions

No diagram questions associated with this lesson