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Simple machines are of the following types:

1. Lever
2. Pulley
3. Inclined plane
4. Wheel and axle
5. Screw
6. Wedge

Lever

A lever is a rigid bar may be straight or bent which is capable of rotating fixed point called fulcrum. In a lever, effort distance and load distance are measured from fulcrum. The distance between fulcrum and load is load distance and fulcrum and effort is effort distance.

Pulley

A pulley is a metallic or wooden disc with a grooved rim. The rim rotates about a horizontal axis passing through its centre.

A pulley can be used in single fixed pulley, single movable pulley or combined form (block and tackle). A single fixed pulley makes our work easier by changing the direction only; mechanical advantage is not gained because value of effort and load distance is equal. But in single movable pulley, mechanical advantage is gained. In a block and tackle, MA and VR are directly proportional with the number of pulleys used. If the number of pulley increases in block and tackle the VR also increases. In the same way MA increases.

VR in pulleys = No. of pulleys used (except in single movable pulley) or number of rope segments that support the load.

We have,
MA = $$\frac{Load}{Effort}$$

Inclined plane

Slanted surface which is used to lift the heavy load by applying less effort is called inclined plane. In this device, the length of slope (l) acts as effort distance and height of slope (h) acts as load distance. The value of length of slope is always greater than value of height of slope; therefore value of VR is always greater than 1.

Input work = E × Ed = E × l (∴ l= length of slope)

Output work = L × L d = L × h (∴ h = height of slope)

VR =$$\frac {l}{h}$$

We have,

MA = $$\frac{Load}{Effort}$$

Wheel and axle

Wheel and axle consists of two coaxial cylinders of different diameters. Some examples of wheel and axle are string roller, screw driver etc. in wheel and axle effort is applied on big cylinder called wheel and load is overcome by small cylinder called axle. The circumference of big cylinder 9wheel) is considered as effort distance and circumference of small cylinder (axle) is known as load distance. Therefore, the calculation of VR in wheel and axle can be done by following formula

VR=$$\frac{circumference \;of \;big \;cylinder}{circumference \;of \;small \;cylinder}$$

Or, VR = $$\frac{2πR}{2πr}$$ [∴circumference = 2 πr]

∴ VR = $$\frac{R}{r }$$(R=Radius of big cylinder (wheel) and r=Radius of small cylinder (axle) )

We have,

MA = $$\frac{Load}{Effort}$$

• A lever is a rigid bar may be straight or bent which is capable of rotating fixed point called fulcrum.
• A pulley is a metallic or wooden disc with a grooved rim. The rim rotates about a horizontal axis passing through its centre.
• Slanted surface which is used to lift the heavy load by applying less effort is called inclined plane.
• Wheel and axle consists of two coaxial cylinders of different diameters.
.

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

A rigid bar that can be turned about a fixed point is called lever.
Principle of lever: When lever is in equilibrium i.e. horizontal position, Effort x effort arm = Load x load arm

The lever are classified into three types on the basis of the position of fulcrum and they are

• First class lever: e.g. hammer, scissors, etc.
• Second class lever: bottle opener, wheel barrow, etc.
• Third class lever: shovel, forceps, fishing rod, etc.

For 2nd class lever, load is in between fulcrum and effort. So, effort arm is always greater than the load arm, MA = . This shows that the value of MA is greater than one.

For 3rd class lever, effort is in between fulcrum and effort. So, effort arm is always less than the load arm, MA = . This shows that the value of MA is less than one.

Tight knot can be opened by using a long spanner because long spanner has long handles which gives longer effort arm than the load arm. So, the MA is greater than one and it magnifies the force applied. As MA =

When load is shifted towards wheel of wheel barrow, load distance decreases ultimately the value of MA increases and it magnifies force which makes our work easier.

A metallic or wooden disc with a grooved rim is called pulley. There are three types of pulley:

1. Single fixed pulley
2. Single movable pulley
3. Combined pulley

A pulley having a fixed axis of rotation is called single fixed pulley.

The pulley along with the load is capable of sliding on the string when an effort is applied upward from the free end is called single movable pulley.

Here, load is supported by only one segment of the string. To raise the load by 'l' m, the free end has to take up 'l'' m of slack.
So, distance travelled by load = l m
Distance travelled by effort = l m
∴ VR = = 1

There is no gain in the mechanical advantage in a single fixed pulley. It merely changes the direction in which the effort is applied to a more convenient one. So, even if it does not magnify force, it is still used.

Here, load is supported by two segments of the string. To raise the load by 'l' m requires each side of the string to shorten by l m. The free end has to take up '2l'' m of slack. So, distance travelled by load = l m
Distance travelled by effort = 2l m
∴ VR = = 2

We know that combined pulley has VR greater than 1but in fixed pulley the VR is 1.Hence, the force applied is magnified in the combined pulley and not in the single fixed pulley. So, it is easier to work with a combined pulley than a fixed pulley.

An inclined plane is a slope or ramp which is used to lift a load more easily or by using a little effort than the load. It is called a simple machine because it works in small time as well as it makes our work easier.

Mountainous roads act as a inclined plane in which if slope is made longer than height, mechanical advantage will be more and it makes easy to overcome the slope.

Screw is a simple machine having circular thread on its circumference.
The distance between two consecutive thread is known as pitch.

A system, formed by the combination of two co-axial cylinders in which the cylinder with larger radius is arranged to revolve on the cylinder with the smaller radius to facilitate the motion for various mechanical purposes is known as wheel and axle.

When load is connected to axle and effort is on the wheel, it acts as a first class lever with fulcrum in the middle. The ordinary lever can be turned by an effort through an angle less than 900 but wheel and axle can even turn 3600 continuously. So, it is called a continuous lever.

Wedge is a simple machine having two inclined planes such that one end is sharp and the other end is blunt. Example: knife, axe, blade, etc.

Radius of wheel (R) = 6cm = 6/100 = 0.06m
Radius of axle (r) = 2cm = 2/100 = 0.02 m
Effort (E) = 100N
If friction is neglected, MA = VR,
Or, =
Or, =
Or, L = 3 x 100 = 300N
Hence, the maximum load that can be lifted is 300N.

Effort (E) = ?
Efficiency (η) = 80%
Radius of wheel (R) = 8cm = 0.08m
Radius of axle (r) = 2cm – 0.02m
According to formula of efficiency,
η = x 100%
or, η = x 100%
or,80% = x 100%
or, E x 6.4 = 16 x 100
or, E = 1600/6.4
or, E = 250N
Hence, 250N effort is needed to balance.

0%
• ### What does MA stand for in simple machines?

Minimum average
Mechanical Automatic

(m/s)/(m/s)
no unit
M/s
m/m
• ### What is a fulcrum?

the end point of a lever
the middle point of lever
the movable point of lever
the fixed point of a lever

First class

fourth class

second class

third class

• ### VR of pulley is equal to

number of segments supporting the load
number of pulleys
number of segments connecting pulley
number of segments in the load

to decrease MA
it is cheap
to increase length of inclined plane
to provide less friction
• ### Which is implementation of 2nd class lever?

Cutting paper with scissors
Pushing a wheelbarrow
digging with a shovel
rowing a boat with ors
• ### Which is implementation of 3rd class lever?

using nutcracker to break a nut
using hammer to take out a nail from plywood
Using tweezers to pluck hair
Using a jack to lift a car
• ### Why is it easier to open a bolt if the length of the wrench is longer?

Because it increases turning effect
Because wrench with longer handle are stronger
Because a longer handle overcomes friction more easily than shorter handle
Because it is easier to hold a wrench with long handle

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