■Simple Machines

There are six basic types of simple machines: the inclined plane, the wedge, the screw, the lever, the

wheel and axle, and the pulley.

A ramp or an inclined plane is a flat, slanted surface

that allows you to exert your input force over a longer

distance As a result, the input force needed is less

than the output force. The input force that you use on

an inclined plane is the force with which you push or

pull an object. The output force is the force that you

would need to lift the object without the inclined

plane. This force is equal to the weight of the object

without the inclined plane. The larger, or longer, the incline, the less effort you need to push or pull an

object on the inclined plane.

A wedge is a device that is thick at one end and tapers to a thin edge at the other end.

It basically is an inclined plane that moves. It looks like two

inclined planes put together. The longer and thinner a wedge

is, the greater its mechanical advantage. For example, the

cutting edge of a steel carving knife is a wedge. When you

sharpen a knife, you make the wedge thinner and increase its

mechanical advantage. That is why sharp knives cut better than dull knives.

A screw can be thought of as an inclined plane wrapped around a central cylinder,

forming a spiral. This spiral inclined plane forms the threads of the screw. When you

twist a screw into a piece of wood, you exert an input

force on the screw. The threads of a screw act like an inclined plane to

increase the distance over which you exert the input force. As the

threads of the screw turn, they exert an

output force on the wood, pulling the

screw into the wood. Friction between

the screw and the wood holds the screw

in place. Many devices act like screws.

Examples include bolts, light bulbs, and

jar lids. Look at the jar lid in the picture.

When you turn the lid, your small input force is greatly increased because of the screw threads on the

■lid. The threads on the lid are pulled against the matching threads on the jar with a strong enough

force to make a tight seal. The closer together the threads of a screw are, the greater the mechanical

advantage. This is because the closer the threads are, the more times you must turn the screw to

fasten it into a piece of wood. Your input force is applied over a longer distance. 

A lever is a rigid bar

that is free to pivot,

or rotate, about a

fixed point. The fixed

point that a lever

rotates around is

called the fulcrum.

To understand how

levers work, think

about using a paint-

can opener. The

opener rests against

the edge of the can,

which acts as the

fulcrum. The tip of

the opener is under

the lid of the can.

When you push

down, you exert an

input force on the

handle, and the

opener pivots on the

fulcrum. As a result, the tip of the opener pushes up, thereby exerting an output force on the lid.

A lever like the paint-can opener helps you in two ways. It increases your input force and it changes

the direction of your input force. When you use the paint-can opener, you push the handle a long

distance down in order to move the lid a short distance up. However, you are able to apply a smaller

force than you would have without the opener . Levers are classified according to the location of the

fulcrum relative to the input and output forces.

■ A wheel and axle is a simple machine

made of two circular or cylindrical objects

that are fastened together and that rotate

about a common axis. The object with the

larger diameter is called the wheel. The

object with the smaller diameter is called

the axle.

A screwdriver acts as a wheel and axle.

How does a screwdriver make use of a

wheel and axle to do work? Look at the picture. When you use a screwdriver, you apply an input force

to turn the handle, or wheel. Because the wheel is larger than the shaft, or axle, the axle rotates and

exerts a large output force. The wheel and axle increases your force, but you must exert your force

over a long distance.

■

A pulley consists of a rope or cable that is wrapped around a grooved wheel. A pulley that you attach

to a structure is called a fixed pulley. If you attach a pulley to the object you wish to move, you are

using a moveable pulley. Several pulleys can be combined to make a pulley system, or “block and

tackle.” You use a pulley by pulling on one end of the rope. This is the input force. At the other end of

the rope, the output force pulls up on the object you want to move. To move a heavy object over a

distance, a pulley can make work easier in two ways. First, it can decrease the amount of input force

needed to lift the object. Second, the pulley can change the direction of your input force. For example,

you pull down on the flagpole rope, and the flag moves up. The mechanical advantage is measured by

how many ropes are used in the system.

Compound Machines

More complex machines consist of combinations of simple machines. A machine that utilizes two or

more simple machines is called a compound machine. An apple peeler like the one shown in the

picture is a compound machine. Four different simple machines make it up. The handle is a wheel and

axle. The axle is also a screw that turns the apple. A wedge peels the apple’s skin. To hold the machine

in place, a lever can be switched to engage a suction cup. The ideal mechanical advantage of a

compound machine is the product of the individual ideal mechanical advantages of the simple

machines that make it up

■

Name_________________________ Date________Simple Machines

1. What are the six basic kinds of simple machines?

a. b.

c. d.

e. f.

Inclined Plane2. What is an inclined plane?

3.Circle the letter of each sentence that is true about inclined planes.a. The necessary input force is less than the output force.b. A ramp is an example of an inclined plane.c. The necessary input force is more than the output force.d. An inclined plane allows you to exert your force over a longer distance.

4. The larger the incline, the less___________________ you need to push or pull

an object on an inclined plane.

■Wedge5. What is a wedge?

6. True or False? In a wedge, the inclined plane itself moves.

7. True or False? The longer and thinner a wedge is, the greater its mechanical advantage. Screws8.What is a screw?

9. A spiral inclined plane forms the _______________ of a screw.

10. When twisting a screw into a piece of wood, where is the input force applied

and where is the output force exerted?

___________________________________________________________________________

11. What holds the screw and wood in place? _________________________

12. True or False? The farther apart the threads of a screw are, the greater the mechanical advantage

Levers13. What is a lever?

14. The fixed point that a lever pivots around is called the ____________________.

15. Circle the letter of each sentence that is true about levers.a. A lever increases the effect of your input force.b. There are three different types of levers.c. A lever changes the direction of your input force.d. The fulcrum is always located at the same place on a lever.

16. On each diagram below, draw a triangle below the lever to show where the fulcrum is located on each class of lever.

Work and M

achines

■

First-class levers Second-class levers Third-class levers

17. Complete the following table about levers.

Levers

Class of Lever Examples

Door, wheel barrow, bottle Seesaw, scissors, pliersBaseball bat, shovel, fishing

Wheel and Axle18. What is a wheel and axle?

19. The object with the _________________ ____________________ is the wheel, and the smaller

diameter is the ____________________

20. An example of a wheel and axle is a _________________________

Pulley21. What is a pulley?

22. What kind of pulley changes the direction of the input force but does not change the amount of force you apply? ___________________________

23. What kind of pulley has an ideal mechanical advantage of 2? Why?

____________________________________________________________________________

Input

force

Output

force

Input

force

Output

force

Output

force

Input

force

■24. What is a block and tackle pulley? _________________________________________

_______________________________________________________________________

Compound Machines25. What is a compound machine?

26. What do you need to know to calculate the mechanical advantage of a compound machine?

27. Name the 4 simple machines that make up an apple peeler. Describe them.

1. ______________________________________________________________________

2. ______________________________________________________________________

3. _______________________________________________________________________

4. _______________________________________________________________________

■

Simple Machines in the Body27. What do most of the levers in your body consist of?

28.Your muscles are attached to your bones by tough connective tissue called

______________________.

27. In a living lever in your body, what acts as the lever’s fulcrum?

28. What simple machines do your incisors resemble?

________________________________________________________________

29. Explain how your front teeth are like an ax.

________________________________________________________________________________________________________________________________