simple machines

comparing classes of levers

All three classes of levers make work easier, but they do so in different ways. When the input and output forces are on opposite sides of the fulcrum, the lever changes the direction of the applied force. This occurs only with a first-class lever. When both the input and output forces are on the same side of the fulcrum, the direction of the applied force does not change. This occurs with both second- and third-class levers. When the input force is applied farther from the fulcrum, the input distance is greater than the output distance, so the ideal mechanical advantage is greater than 1. This always occurs with second-class levers and may occur with first-class levers. When the input force is applied closer to the fulcrum, the input distance is less than the output distance, so the ideal mechanical advantage is less than 1. This always occurs with third-class levers and may occur with first-class levers. When both forces are the same distance from the fulcrum, the input distance equals the output distance, so the ideal mechanical advantage equals 1. This occurs only with first class-levers.

lever

Did you ever use a hammer to pull a nail out of a board? If not, you can see how its done in Figure 16.18. When you pull down on the handle of the hammer, the claw end pulls up on the nail. A hammer is an example of a lever. A lever is a simple machine consisting of a bar that rotates around a fixed point called the fulcrum. For a video introduction to levers using skateboards as examples, go to this link: MEDIA Click image to the left or use the URL below. URL: A lever may or may not increase the force applied, and it may or may not change the direction of the force. It all depends on the location of the input and output forces relative to the fulcrum. In this regard, there are three basic types of levers, called first-class, second-class, and third-class levers. Figure 16.19 describes the three classes.

wheel and axle

Did you ever ride on a Ferris wheel, like the one pictured in Figure 16.20? If you did, then you know how thrilling the ride can be. A Ferris wheel is an example of a wheel and axle. A wheel and axle is a simple machine that consists of two connected rings or cylinders, one inside the other, which both turn in the same direction around a single center point. The smaller, inner ring or cylinder is called the axle. The bigger, outer ring or cylinder is called the wheel. The car steering wheel in Figure 16.20 is another example of a wheel and axle. In a wheel and axle, force may be applied either to the wheel or to the axle. In both cases, the direction of the force does not change, but the force is either increased or applied over a greater distance. When the input force is applied to the axle, as it is with a Ferris wheel, the wheel turns with less force, so the ideal mechanical advantage is less than 1. However, the wheel turns over a greater distance, so it turns faster than the axle. The speed of the wheel is one reason that the Ferris wheel ride is so exciting. When the input force is applied to the wheel, as it is with a steering wheel, the axle turns over a shorter distance but with greater force, so the ideal mechanical advantage is greater than 1. This allows you to turn the steering wheel with relatively little effort, while the axle of the steering wheel applies enough force to turn the car.

You may be wondering why you would use a third-class lever when it doesnt change the direction or strength of the applied force. The advantage of a third-class lever is that the output force is applied over a greater distance than the input force. This means that the output end of the lever must move faster than the input end. Why would this be useful when you are moving a hockey stick or baseball bat, both of which are third-class levers?

inclined plane

The man in Figure 16.14 is using a ramp to move a heavy dryer up to the back of a truck. The highway in the figure switches back and forth so it climbs up the steep hillside. Both the ramp and the highway are examples of inclined planes. An inclined plane is a simple machine consisting of a sloping surface that connects lower and higher elevations. The sloping surface of the inclined plane supports part of the weight of the object as it moves up the slope. As a result, it takes less force to move the object uphill. The trade-off is that the object must be moved over a greater distance than if it were moved straight up to the higher elevation. On the other hand, the output force is greater than the input force because it is applied over a shorter distance. Like other simple machines, the ideal mechanical advantage of an inclined plane is given by: Ideal Mechanical Advantage = Input distance Output distance For an inclined plane, the input distance is the length of the sloping surface, and the output distance is the maximum height of the inclined plane. This was illustrated in Figure 16.12. Because the sloping surface is always greater than the height of the inclined plane, the ideal mechanical advantage of an inclined plane is always greater than 1. An inclined plane with a longer sloping surface relative to its height has a gentler slope. An inclined plane with a gentler slope has a greater mechanical advantage and requires less input force to move an object to a higher elevation.

wedge and screw

Two simple machines that are based on the inclined plane are the wedge and the screw. Both increase the force used to move an object because the input force is applied over a greater distance than the output force.

wedge

Imagine trying to slice a tomato with a fork or spoon instead of a knife, like the one in Figure 16.15. The knife makes the job a lot easier because of the wedge shape of the blade. A wedge is a simple machine that consists of two inclined planes. But unlike one inclined plane, a wedge works only when it moves. It has a thin end and thick end, and the thin end is forced into an object to cut or split it. The chisel in Figure 16.15 is another example of a wedge. The input force is applied to the thick end of a wedge, and it acts over the length of the wedge. The output force pushes against the object on both sides of the wedge, so the output distance is the thickness of the wedge. Therefore, the ideal mechanical advantage of a wedge can be calculated as: Ideal Mechanical Advantage = Length of wedge Maximum thickness of wedge The length of a wedge is always greater than its maximum thickness. As a result, the ideal mechanical advantage of a wedge is always greater than 1.

screw

The spiral staircase in Figure 16.16 also contains an inclined plane. Do you see it? The stairs that wrap around the inside of the walls make up the inclined plane. The spiral staircase is an example of a screw. A screw is a simple machine that consists of an inclined plane wrapped around a cylinder or cone. No doubt you are familiar with screws like the wood screw in Figure 16.16. The screw top of the container in the figure is another example. Screws move objects to a higher elevation (or greater depth) by increasing the force applied. When you use a wood screw, you apply force to turn the inclined plane. The output force pushes the screw into the wood. It acts along the length of the cylinder around which the inclined plane is wrapped. Therefore, the ideal mechanical advantage of a screw is calculated as: Ideal Mechanical Advantage = Length of inclined plane Length of screw The length of the inclined plane is always greater than the length of the screw. As a result, the mechanical advantage of a screw is always greater than 1. Look at the collection of screws and bolts in Figure 16.17. In some of them, the turns (or threads) of the inclined plane are closer together. The closer together the threads are, the longer the inclined plane is relative to the length of the screw or bolt, so the greater its mechanical advantage is. Therefore, if the threads are closer together, you need to apply less force to penetrate the wood or other object. The trade-off is that more turns of the screw or bolt are needed to do the job because the distance over which the input force must be applied is greater.

instructional diagrams

Shown in the diagram are the six types of simple machines. A simple machine is a mechanical device that makes work easier. It includes the inclined plane, wedge, lever, wheel and axle, screw and pulley. An inclined plane is a flat surface that is slanted, or inclined, so it can help move objects across distances. A common inclined plane is a ramp used to lift heavy objects in a back of a truck. Instead of using the smooth side of the inclined plane to make work easier, you can also use the pointed edges to do other kinds of work. When you use the edge to push things apart, this movable inclined plane is called a wedge. An ax blade is one example of a wedge. Any tool that pries something loose is a lever. Levers can also lift objects. A lever is an arm that turns against a fulcrum (the point or support on which a lever pivots). Think of the claw end of a hammer that you used to pry nails loose; it's a lever. The Wheel and Axle makes work easier by moving objects across distances. The wheel (or round end) turns with the axle (or cylindrical post) causing movement. On a wagon, for example, a container rests on top of the axle to help transport heavy objects. A Screw helps you do work is that it can be easily turned to move itself through a solid space like turning a jar cover to keep it the jar air tight. Instead of an axle, a wheel could also rotate a rope, cord, or belt. This variation of the wheel and axle is the pulley. In a pulley, a cord wraps around a wheel. Instead of an axle, you can use the wheels rotation to raise and lower objects, making work easier. On a flagpole, for example, a rope is attached to a pulley to raise and lower the flag more easily.

questions

Which type of simple machine is a chisel?

``````a. lever

b. screw

-->  c. wedge

d. none of the above
``````

Which type of simple machine is the head of an axe?

``````-->  a. wedge

b. lever

c. screw

d. none of the above
``````

Which of the following is an example of a screw?

``````-->  a. spiral staircase

b. Ferris wheel

c. seesaw

d. axe
``````

Which of the following is a second-class lever?

``````a. seesaw

b. chisel

-->  c. wheelbarrow

d. hockey stick
``````

The ideal mechanical advantage of a screw is always

``````a. less than 1.

b. equal to 1.

-->  c. greater than 1.

d. greater than 2.
``````

The ideal mechanical advantage of a pulley equals the

``````-->  a. number of rope segments lifting up on the object.

b. length of the rope segments between the pulley and the object.

c. height of the pulley above the surface of the ground.

d. number of rope segments between the pulley and the beam.
``````

Which statement about a wheel and axle is true?

``````a. It consists of two simple machines.

b. It changes the direction of the applied force.

-->  c. It changes the distance over which the force is applied.

d. two of the above
``````

Which class of lever does not change the direction of the applied force?

``````a. class 1

b. class 2

c. class 3

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

Which of the following is an example of a third class lever?

``````a. seesaw

b. wheelbarrow

-->  c. hockey stick

d. pry bar
``````

The ideal mechanical advantage of an inclined plane is always

``````a. less than one.

b. equal to one.

-->  c. greater than one.

d. less than zero.
``````

A wheel and axle increase the applied force when

``````a. the input distance is equal to the output distance.

b. the input distance is less than the output distance.

-->  c. the input force is applied to the wheel.

d. the output force is applied by the wheel.
``````

How many rope segments pull up on the object in a single moveable pulley?

``````a. 1

-->  b. 2

c. 3

d. 4
``````

There are seven different types of simple machines.

``````a. true

-->  b. false
``````

The input distance of an inclined plane is always greater than the output distance.

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

b. false
``````

The input force is always applied to the thinner side of a wedge.

``````a. true

-->  b. false
``````

The center of a wheel and axle is called the fulcrum.

``````a. true

-->  b. false
``````

The closer together the threads of a screw are, the harder it is to turn the screw.

``````a. true

-->  b. false
``````

A wedge is used to cut or split objects.

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

b. false
``````

When you use a hammer to pry a nail out of board, the hammer is a first class lever.

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

b. false
``````

A lever always increases the force applied to the lever.

``````a. true

-->  b. false
``````

When you turn a screw, you apply force along its inclined plane.

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

b. false
``````

The wheel of a Ferris wheel turns more quickly than the axle.

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

b. false
``````

A lever may or may not change the strength of the applied force.

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

b. false
``````

The wheel of a wheel and axle turns more slowly than the axle.

``````a. true

-->  b. false
``````

A single fixed pulley has an ideal mechanical advantage of 1.

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

b. false
``````

A compound pulley always contains at least two fixed pulleys.

``````a. true

-->  b. false
``````

A zip-line pulley is an example of a single moveable pulley.

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

b. false
``````

simple machine that consists of a rope and grooved wheel

``````a. inclined plane

b. class 2 lever

-->  c. pulley

d. screw

e. class 1 lever

f. wheel and axle

g. fulcrum
``````

type of lever in which the fulcrum is between the input and output forces

``````a. inclined plane

b. class 2 lever

c. pulley

d. screw

-->  e. class 1 lever

f. wheel and axle

g. fulcrum
``````

simple machine consisting of two connected rings or cylinders that both turn around a single center point

``````a. inclined plane

b. class 2 lever

c. pulley

d. screw

e. class 1 lever

-->  f. wheel and axle

g. fulcrum
``````

simple machine that consists of an inclined plane wrapped around a cylinder or cone

``````a. inclined plane

b. class 2 lever

c. pulley

-->  d. screw

e. class 1 lever

f. wheel and axle

g. fulcrum
``````

fixed point of a lever around which the bar rotates

``````a. inclined plane

b. class 2 lever

c. pulley

d. screw

e. class 1 lever

f. wheel and axle

-->  g. fulcrum
``````

simple machine consisting of a sloping surface that connects lower and higher elevations

``````-->  a. inclined plane

b. class 2 lever

c. pulley

d. screw

e. class 1 lever

f. wheel and axle

g. fulcrum
``````

type of lever in which input and output forces are on the same side of the fulcrum

``````a. inclined plane

-->  b. class 2 lever

c. pulley

d. screw

e. class 1 lever

f. wheel and axle

g. fulcrum
``````

diagram questions

By what letter is the fulcrum represented in the diagram?

``````-->  a. R

b. K

c. E

d. N
``````

Which letter indicates the fulcrum?

``````a. P

b. K

-->  c. R

d. J
``````

Which letter represents a fulcrum?

``````a. M

b. N

-->  c. R

d. E
``````

Which letter corresponds to the part where a lever rests?

``````a. P

-->  b. R

c. A

d. Y
``````

By what letter is the screw represented in the diagram?

``````a. E

b. L

-->  c. J

d. C
``````

What is the machine represented with the letter L?

``````-->  a. INCLINED PLANE

b. WEDGE

c. LEVER

d. PULLEY
``````

Identify the lever in this picture

``````-->  a. E

b. L

c. C

d. J
``````

Which machine would be best for transporting bricks?

``````a. E

b. L

-->  c. C

d. J
``````

Which label refers to the axel?

``````a. M

b. P

-->  c. S

d. J
``````

Identify the axle in the following image:

``````a. M

-->  b. S

c. P

d. F
``````

By what letter is the pulley represented in the picture?

``````a. K

b. U

c. L

-->  d. M
``````

Identify the lever in this picture

``````a. N

b. K

-->  c. L

d. M
``````

A pulley uses some form of a rope and wheel. Which picture is a pulley?

``````-->  a. M

b. L

c. K

d. U
``````

A simple machine that consists of a rope and grooved wheel. What am I?

``````a. WEDGE

b. LEVER

c. SCREW

-->  d. PULLEY
``````

Identify nutcracker in this picture

``````-->  a. W

b. S

c. A

d. P
``````

Which represents a pair of tongs?

``````-->  a. A

b. X

c. P

d. W
``````

Find the lever.

``````a. V

b. F

-->  c. E

d. L
``````

Which label represents the screw?

``````a. E

b. M

-->  c. P

d. L
``````

What simple machine requires some kind of balance beam?

``````a. pulley

-->  b. lever

c. inclined plane

d. wheel and axle
``````

In a pulley, what happens to the load when force is applied?

``````a. The load goes down

-->  c. The load goes up

``````

What are the two elements needed for a pulley?

``````-->  a. Load and Force

c. Force and Lever

d. Wheel and Force
``````

How many simple machines are shown in the diagram?

``````a. 5

-->  b. 6

c. 4

d. 7
``````

What simple machine should you used to lift heavy object from one point to another?

``````-->  a. the pulley and the lever

b. wedge

c. screw

d. inclined plane
``````

How do you prevent the load from falling down?

``````a. release the load

b. Decrease effort force

-->  c. Increase effort force

d. increase gravitational force
``````

What is a pulley used for?

``````a. suspend load

c. use as a compound

``````

How many pulleys does the compound pulley in the diagram consist of?

``````a. 3

b. 1

c. 4

-->  d. 2
``````

A compound pulley is composed of what?

``````-->  a. a fixed and a movable pulley

b. two fixed and two movable pulleys

c. two movable pulleys

d. two fixed pulleys
``````

Which label shows a single movable pulley?

``````a. D

b. C

-->  c. B

d. A
``````

How many wheels are there in pulley D?

``````a. 2

b. 4

c. 1

-->  d. 3
``````

How many wheels in pulley D?

``````-->  a. 3

b. 5

c. 1

d. 2
``````

Which letter represents that the object has been fully raised up by the pully?

``````a. B

b. A

-->  c. D

d. C
``````

Which pulley system would require the least energy to life the weight?

``````a. C

b. A

c. B

-->  d. D
``````

What is the simple machine shown in the diagram?

``````a. wedge

b. ramp

c. lever

-->  d. pulley
``````

When load increases, what needs to happen to effort?

``````a. It must decrease to lift the load

b. It must stay the same

c. It must change the mechanical advantage

-->  d. It must increase to lift the load
``````

How much is the ideal mechanical advantage?

``````-->  a. 1

b. 2

c. 3

d. 4
``````

What moves the axle?

``````a. only effort

b. only resistance

-->  c. the wheel and effort

d. only the wheel
``````

When the man turns the wheel in a clockwise manner, what is the direction of the motion?

``````-->  a. upward

b. counter-clockwise

c. downward

d. sideways
``````

Which machine consists of a sloping surface that connects lower and higher elevations?

``````a. Screw

-->  b. Inclined Plane

c. Pulley

d. Lever
``````

This is a simple machine consisting of a sloping surface that connects lower and higher elevations.

``````a. Screw

b. Pulley

c. Lever

-->  d. Inclined plane
``````

How many simple machines is shown in the figure?

``````a. 4

b. 3

c. 2

-->  d. 5
``````

What is a wheel with a grooved rim around which a cord passes?

``````a. Screw

-->  b. Pulley

c. Lever

d. Wedge
``````

What type of pulley is indicated in the drawing?

``````-->  a. Compound pulley

b. Single Fixed Pulley

c. lever pulley

d. Single movable pulley
``````

How can the man prevent the load from falling down?

``````a. Increase the load

b. Decrease the pull on the rope

c. Release the rope

-->  d. Increase the pull on the rope
``````

How many pulleys are there in the diagram?

``````a. 3

-->  b. 1

c. 2

d. 4
``````

How many wheels on a pulley?

``````a. 2

b. 4

-->  c. 1

d. 3
``````

What is the man using to help him lift the heavy load?

``````a. wedge

-->  b. pulley

c. inclined plane

d. lever
``````

What simple machine is shown in this picture?

``````a. Screw

b. Wedge

c. Lever

-->  d. Pulley
``````

A seesaw is an example of what simple machine?

``````a. ramp

-->  b. lever

c. wedge

d. pulley
``````

Which of these is NOT a Lever?

``````-->  a. Bottle

b. Nut Cracker

c. Seesaw

d. Pair of Tongs
``````

In a pair of scissors, what is located in the middle of the load and the applied force?

``````a. applied force

b. wheel

-->  c. Fulcrum

``````

How many examples of lever in daily life are shown?

``````a. 3

-->  b. 6

c. 4

d. 5
``````

What is an example of a lever in daily life that is used by two people to play at the same time?

``````a. Nut cracker

-->  b. Seesaw

c. Fishing Rod

d. Pair of tongs
``````

What is a sloping ramp up which heavy loads can be raised by ropes or chains?

``````a. Lever

b. Pulley

c. Skewer

-->  d. Inclined Plane
``````

What is the object called that makes pushing the wheelbarrow easier?

``````a. elevator

b. stairs

-->  c. inclined plane

d. sand
``````

How many wheels does the wheelbarrow have?

``````a. 3

-->  b. 1

c. 4

d. 2
``````

In the diagram what is the man pushing the wheel barrow up?

``````-->  a. Inclined plane

b. Turning left

c. Level

d. Down a hilll
``````

What is the man using to help him push the wheelbarrow up?

``````a. pulley

b. wedge

c. lever

-->  d. inclined plane
``````

What happens if you pull the cord on the first image?

``````a. The object doesn't move

b. The object falls

-->  c. The object rises

d. The object goes down
``````

How many pulleys shown in the figure?

``````a. 1

b. 0

c. 3

-->  d. 2
``````

Which simple machine consists of an inclined plane wrapped around a cylinder or cone?

``````a. 1) Lever

-->  b. 3) Screw

c. 6) Pulley

d. 5) Wedge
``````

Which of the following types of simple machines is used to bind two physical objects together?

``````a. Pulley

b. Inclined plane

-->  c. Screw

d. Wedge
``````

How many types of simple machines are there?

``````a. 2

-->  b. 6

c. 8

d. 4
``````

How many types of simple machines is shown in the diagram?

``````a. 3

-->  b. 6

c. 4

d. 5
``````

A crowbar would be considered which one of these simple machines?

``````a. screw

-->  b. Lever

c. wedge

d. inclined plane
``````

Which number shows a wheel with a grooved rim around which a cord passes?

``````a. 1

b. 4

c. 3

-->  d. 6
``````

How many pulleys are being used here?

``````a. 4

b. 2

c. 3

-->  d. 1
``````

What is the simple machine shown in the diagram?

``````a. lever

b. wedge

-->  c. pulley

d. inclined plane
``````

How many pivots does this lever have?

``````a. 2

b. 0

c. 3

-->  d. 1
``````

What equipment is the man using to move the rock?

``````a. Truck

b. Bulldozer

-->  c. Rod

d. Crane
``````

What is the man trying to carry?

``````a. Table

b. Tree

-->  c. Rock

d. Wood
``````

Which is a more complex pulley system?

``````a. a

-->  b. c

-->  c. d

d. B
``````

What simple machine is found here?

``````a. lever

b. screw

-->  c. pulley

d. rope
``````

Identify the wedge

``````a. L

b. P

c. E

-->  d. M
``````