Notes on Simple Machine | Grade 7 > Science > Simple Machine | KULLABS.COM

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### Introduction

We use various types of machine in our daily life to perform various activities. These machines make our work easy and efficient. For example, we use a knife to chop vegetables, scissors to cut papers, beam balance to measure weight, bottle opener to open the bottle, etc. There are a simple machine and complex machine. Forceps, punching machine, crowbar, bottle opener, etc. are examples of the simple machine while motorcycle, truck, car, etc. are some examples of the complex machine. A simple machine is a device, which is simple in structure and makes our daily work easier, faster and more convenient.

### Types of Simple Machines

Mainly, there are six types of simple machines, which are given below,

• Lever
• Wheel and axle
• Screw
• Pulley
• Inclined plane
• Wedge

#### Lever

Lever is a type of simple machine that is used to lift the heavy loads. It is made of a rigid bar that moves about a fixed point called fulcrum. It consists of three parts, effort arm, fulcrum and load arm. Fulcrum is the point where rigid bar rotates. By applying effort in effort arm the load is lifted by the help of fulcrum. Effort arm is the distance between the fulcrum and the point where effort is applied and load arm is the distance between fulcrum and load where the load is kept. Input work is equal to output work in an ideal lever which is the balanced condition of the lever. It is the principle of the lever.
Levers are of three types depending upon the positions of fulcrum, load, and effort which are as follows,

1. First class lever: In the first class lever, fulcrum lies between effort and the load. Effort arm is longer than load arm. Beam balance, scissors, crowbar, etc are some examples of the first class lever.
2. Second class lever: In the second class lever, the load is placed between the fulcrum and the effort. Since effort arm is longer than load arm it multiplies the applied effort which helps to lift the heavy load by applying small effort. Wheel-barrow, nut- cracker, paper- cutter, etc. are some examples of the second class lever.
3. Third class lever: In the third class lever, the effort is located in between fulcrum and load. Here, effort arm is shorter than the load arm. It cannot lift the heavy load but increases the speed of doing work. Fire tongs, fishing rod, shovel, etc. are the examples of the third class lever.

Activity 1

Bring a rigid bar, one heavy stone, and two bricks. Then, lift the stone without using a rigid bar. Place stone in the one end of the bar and place the middle part of the bar in the bricks of a certain height. Then, apply the effort on the other end of the bar. What do you conclude from this experiment? What is the reason behind it?

#### Pulley

A pulley is a simple machine consisting grooved circular disc and a rope. The rope passes over the circular disc. In pulley, a load is attached to one end of the rope while the effort is applied at the another end of the same rope. Here, the effort is applied in a convenient way which makes our work easier. There are two types of the pulley on the basis of their movements. They are as follows,

1. Fixed pulley: In fixed pulley, the pulley remains in the same position or fixed at the point while the pulley’s wheel moves with the rope that passes through it while raising the load. It is used to lift water from well. It is also used in flag poles.
2. Movable pulley: In movable pulley, the pulley moves with the load. Both load and pulley move upward when the rope is moved upward. One end of the rope is fixed at one point and effort is applied to another point. Here, applied effort is equally shared by both parts of the rope due to which we can lift the load two times heavier than the applied effort. For example, we can uplift the load of 20N by applying 10N effort.

Activity 2

Lift the water from the well by using a pulley. The water bucket moves upward though you are pulling the rope downward. What do you conclude from this experiment? What is the reason behind this?

#### Wheel and axle

It consists of two cylinders having a different radius. Cylinder with a small radius is axle and cylinder with a large radius is a wheel. Formally, a rope is coiled in wheel and axle. The effort is applied in wheel and load in the axle. They move in the same manner but the distance covered is different due to the difference in radius. Since effort applied on the wheel is magnified so, by applying small effort on the wheel, heavy loads can be lifted. Some of the examples of wheel and axle are paddle of the bicycle, a drill used by carpenters, steering of vehicles, etc.

Activity 3

Ride and use the paddle of the bicycle. You can find that the tyres move faster though you paddle slowly. What do you conclude from this experiment? What is the reason behind this ?

#### Inclined plane

It is very difficult to load heavy things onto a truck or some area of a certain height. A huge effort is needed. In such case, the inclined plane is used. It is a sloping surface or a wooden plank. It multiplies the applied effort. It helps to push the heavy load upward easily. The winding road, staircase, ladder, etc. are the examples of an inclined plane.

Activity 4

Bring a sloping surface or a wooden plank and a heavy load like a small drum. Then lift the drum up to the certain height without using the wooden plank. After this, again lift the drum in the same height by using wooden plank i.e. inclined plane. What do you conclude from this two activity? What is the reason behind it?

#### Screw

A screw is an inclined plane wrapped around a nail. It consists of circular edges called thread. The pitch is the distance between two screw thread. The effort is applied to the head of the screw. It looks similar to nail and requires less effort to insert into the wood. Screw, nail, jack screw, etc.are some of the examples of the screw.Jack screw is used to lift the vehicles up to the certain height.

Activity 5

Bring a screw and the wood. Then insert the screw in the wood by rotating its head instead of pressing it inside. The screw moves downward though we don’t press the screw. What is the reason behind it?

#### Wedge

A wedge is a triangular shaped tool. Wedge consists of two or more sloping surfaces with one end sharp or pointed edge while the other one is a blunt edge. Here, the effort is applied at the blunt side. It is mainly used for cutting and splitting things, drilling holes etc. Some of the examples of wedges are axe, knife, nail, sickle, etc.

Activity 6

Bring a knife and a small piece of wood. Then cut the piece of wood with the help of the knife. Though you hit the piece of wood in the straight direction or apply force in one direction (vertical), the woods gets separated (horizontal force). What is the reason behind it?

Activity 7

Identify the simple machines given below. Classify them and write down their uses and types. What do you learn from this activity? Write down your conclusion.

 S.N. Names of simple machine Types of Simple machine Uses

### Importance of Simple Machine

The importances of simple machine is as follows:

• It can transfer force from one place to another.
• It increases the amount of a force so that we can lift heavier objects or exert greater force with the help of a simple machine.
• It can change the direction of the force so that we can move objects in another direction.
• It increases the distance and speed of force so that we can move things farther and faster.
• The simple machine makes our work easy, fast and more convenient.

• Lever is a type of simple machine that is used to lift the heavy loads.
•  In the first class lever, fulcrum lies between effort and the load.
• A pulley is a simple machine consisting grooved circular disc and a rope.
• A screw is an inclined plane wrapped around a nail.It consists of circular edges called thread.
• A wedge is a triangular shaped tool. Wedge consists of two or more sloping surfaces with one end sharp or pointed edge while the other one is a blunt edge.

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#### Click on the questions below to reveal the answers

Any five types of simple machine with two example of each are given below,

1. Lever
Examples: see- saw and nut- cracker
2. Wheel and axle
Examples: screw- driver
3. Inclined plane
4. Screw
Examples: nail and driller
5. Wedge
Examples: sickle and knife

A lever is a rigid bar which moves freely about a fixed point called the fulcrum. There are three types of lever which are as follows,

1. First class lever
Examples: Beam balance and see- saw
2. Second class lever
Examples: Wheel- barrow and nut- cracker
3. Third class lever

The work done on a machine is called the input work and the useful work done by the machine is called the output work. The principle of lever is given below,
In ideal lever when it is in balanced condition then,
Input work = output work
Or, Effort $$\times$$ effort arm = Load \(\times) load arm.

A wedge is a simple machine having two or more sloping surfaces that taper either to form a sharp edge or pointed edge. Any three examples of wedge are axe, knife, and needle.

Any three advantages of using simple machines in our daily life are as follows,

• It makes or work easier, faster and more convenient.
• It increases the amount of a force so that we can lift heavier objects or exert greater force with the help of simple machine.
• It change direction of the force so that we can move objects in another direction.

A pulley is a simple machine having a grooved circular disc over which a rope passes. There are three types of pulley which are as follows,

1. Fixed pulley: In fixed pulley, the pulley does not move as the load is raised. It is used to lift water from the well.
2. Movable pulley: If the pulley moves along with the load, then it is called movable pulley. Construction crane and modern elevator are the examples of movable pulley.
3. Combined pulley: Combined pulley is a type of pulley that consists of the combination of fixed pulley and movable pulley. Crane used to lift heavy objects is an example of combined pulley.

A second class lever is a type of lever in which load is situated between the fulcrum and the effort. Since in bottle opener, the load ( bottle cork) is situated between the fulcrum and effort so the bottle opener is a second class lever.

Simple machines: Beam- balance, nut- cracker, flag pole, screw- driver, ladder, nail and axe.
The simple machines with their types are given below,

• Beam- balance: first class lever
• Nut- cracker: second class lever
• Flag pole: fixed pulley
• Screw- driver: Wheel and axle
• Nail: screw
• Axe: wedge

Any five simple machines used in our homes are as follows,

1. Knife: It is used to cut vegetables.
2. Beam- balance: It is used to measure the weight or mass.
3. Bottle- opener: It is used to open the cork of the bottle.
4. Paper- cutter: It is used to cut the papers.
5. Lemon- squeezer: it is used to squeeze the lemon.

In second class lever, load is situated between the fulcrum and the effort and in third class lever the effort is situated between the fulcrum and the load. Since in shovel, the effort is situated between the fulcrum and load so it is called third class lever but not a second class lever.

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Effort arm
Fulcrum
Mid arm
• ### Which one of the following is not the example of lever ?

Screw
Beam balance
Crowbar
Paper- cutter
• ### Which one of them is an example of third class lever ?

Shovel
Paper- cutter
Beam balance
Crowbar
• ### Which one of them is a example of second class lever ?

Crowbar
Screw
Paper- cutter
Beam balance
• ### Which types of pulley is used to lift the water from the well ?

Combined pulley
Lever pulley
Fixed pulley
Movable pulley
• ### Paddle of bicycle is the example of

Pulley
Lever
Screw
Wheel and axle
• ### Which one of them is an example of wheel and axle ?

Crowbar
Beam balance
Paper- cutter
Screw- driver
• ### Drill used by carpenters is an example of

Wheel and axle
Lever
Wedge
Pulley
• ### Which one of the following is an example of Screw ?

Jack- screw
Forceps
paper- cutter
Screw- driver

Screw
Crowbar
Knife
Beam balance

Knife
Needle
Nut- cracker
Axe

Pulley
Lever
Screw
Wedge

Pitch
Edge
Grooves
Cone
• ### If the pulley moves along with the load then it is called

Fixed pulley
stationery pulley
Movable pulley
Lever pulley

Fulcrum arm
Effort arm
• ### The distance between fulcrum and the point at which load acts is called

Effort arm
Fulcrum arm
Effort distance

Screw
Pulley
Wedge
Lever
• ### The lever in which the load is situated between the fulcrum and the effort is called

First class lever
Fourth class lever
Second class lever
Third class lever
• ### The lever in which the effort is situated between the load and the fulcrum is called

Third class lever
Second class lever
First class lever
Fourth class lever
• ### The lever in which the fulcrum is situated between the load and the effort is called

Third class lever
First class lever
Fourth class lever
Second class lever

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