Simple Machines

$\frac{\text {Load}}{\text {Effort}}$

Reason — The factor by which a machine multiplies the force applied (i.e. effort) is called the mechanical advantage of that machine and it is the ratio of the load to the effort. In other words,

${\text{Mechanical Advantage} =\frac{\text{Load}}{\text{Effort}}}$

equal to unity

Reason — For an ideal machine, the work output is equal to the work input, i.e., the efficiency of an ideal machine is 1 or equal to unity.

$\frac{\text {Effort Arm}}{\text {Load Arm}}$

Reason — According to the principle of a lever the mechanical advantage of a lever is equal to the ratio of the effort arm to the load arm and is given by :

$\text {Mechanical Advantage}=\frac{\text {Load}}{\text {Effort}}=\frac{\text {Effort Arm}}{\text {Load Arm}}$

helps to apply the force in a convenient direction

Reason — A pulley is a simple machine by which the direction of effort is changed to raise up a load.

rolling friction is less than the sliding friction

Reason — When a wheel rotates on its axle, the contact surfaces roll instead of slide. Rolling friction is much smaller than sliding friction, so using a wheel-and-axle arrangement greatly reduces the resistive force and makes it easier to move loads.

Both A and R are true and R is the correct explanation of A

Explanation

Assertion (A) is true because the mechanical advantage (MA) of a lever is given by,

$\text {MA} = \frac{\text {Load}}{\text {Effort}} \quad \quad [\textbf {Equation 1}]$

So, when the effort required is greater than the load then the mechanical advantage of such type of lever is less than one.

Reason (R) is true because mechanical advantage of a lever is also given by,

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

By using Equation 1,

$\frac{\text {Effort arm}}{\text {Load arm}} = \frac{\text {Load}}{\text {Effort}}$

So, if the effort arm is shorter than the load arm, a larger effort is needed to balance the load.

The Reason justifies the Assertion because when the effort arm is shorter, the effort becomes greater than the load, making the mechanical advantage less than 1.

Therefore, both A and R are true and R is the correct explanation of A.

A is false but R is true

Explanation

Assertion (A) is false because a forearm holding a load is an example of a class III lever, not class II. In this case, the effort (applied by muscles) lies between the fulcrum (elbow joint) and the load (held in the hand).

Reason (R) is true because in a class II lever, the load is positioned between the fulcrum and the effort.

Therefore, A is false but R is true.

(a) The useful work done by an actual machine is always less than the work done on the machine.

(b) In class II levers, the load is in between fulcrum and effort .

(c) The mechanical advantage of class III lever is always less than 1.

(d) A pulley is used to change the direction of effort.

(e) Mechanical advantage of an inclined plane is always greater than 1.

(a) False because work is said to be done if the force applied on the body moves it. If no motion or change in position takes place, no work is said to be done so when a boy pushes a wall, no work is done by him since wall remains stationary.

(b) False because a machine can do useful work only when energy is supplied to it; it cannot work by itself.

(c) True because a machine in which no part of the work done on the machine is wasted, is called an ideal or perfect machine. Thus, for an ideal machine, the work done on load is equal to the work done by effort.

(d) False as Class I and Class II levers can act as force multipliers when the effort arm is longer than the load arm, but Class III levers have the effort applied closer to the fulcrum and thus do not multiply force.

(e) True because a pulley is a simple machine by which the direction of effort is changed to raise up a load.

(f) True because the effort required to push a load up an inclined plane is less than the load. Thus, the mechanical advantage of an inclined plane is always greater than 1.

Work is said to be done if the force applied on the body moves it. If no motion or change in position takes place, no work is said to be done.

The energy of a body is its capacity (or ability) to do work.

A machine is a device which helps us to do work more easily by applying less force and spending less energy.

A machine does not work by itself. When energy is supplied to it (or work is done on it), it does some useful work. Hence, the machine works on the principle of conservation of energy.

A machine has the following functions :

1. It decreases the magnitude of the force required, i.e., the effort is less than the load.
2. It changes the direction of effort in a convenient direction.

Work Input : The work done on a machine by the effort (input force) is called work input.

Work Output : The work done by the machine on the load is called work output.

The factor by which a machine multiplies the force applied (i.e. effort) is called the mechanical advantage of that machine. It is the ratio of the load to the effort.

$\text {Mechanical Advantage} = \frac{\text {Load}}{\text {Effort}}$

The efficiency of a machine is the ratio of the useful work done by the machine to the work put into the machine by the effort. Thus,

$\text {Efficiency} = \frac{\text {Work output on load}}{\text {Work input by effort}}$

A machine in which no part of the work done on the machine is wasted i.e., the efficiency of the machine is 1 or 100 per cent, is called an ideal or perfect machine.

In practice, no machine has an efficiency of 100% because some part of the work done on a machine is always used up (or wasted) in overcoming the friction between the moving parts of the machine. Therefore, the work output of a machine is always less than the work input.

If a machine is 75% efficient, it means that 75% of the work input to the machine is obtained as the useful work output and the remaining 25% of the work input has been wasted in overcoming friction.

A lever is a simple machine which in its simplest form is made up of a rod which can turn about a fixed point called the fulcrum.

The mechanical advantage of a lever is equal to the ratio of the effort arm to the load arm and is given by :

$\text {Mechanical Advantage}=\frac{\text {Load}}{\text {Effort}}=\frac{\text {Effort Arm}}{\text {Load Arm}}$

The mechanical advantage of class II levers is always more than 1. Example : nut cracker.

The mechanical advantage of class III levers is always less than 1. Example : knife.

(i) A pair of pliers

(ii) Beam balance

(iii) Pair of scissors

(a) A pair of scissors → Class I lever

(b) A lemon squeezer → Class II lever

(c) A nutcracker → Class II lever

(d) A pair of sugar tongs → Class III lever

(e) A beam balance → Class I lever

(f) An oar oar rowing a boat → Class I lever

(g) A wheelbarrow → Class II lever

(h) A seesaw → Class I lever

(i) A pair of pliers → Class I lever

(j) A crowbar → Class I lever

Three kinds of friction are as follow :

(a) Class II lever
Example: Wheel barrow

(b) Class I lever
Example: Pair of scissors

(c) Class III lever
Example: Knife

The mechanical advantage of a lever can be increased by increasing the effort arm or reducing the load arm.

Friction at the fulcrum uses up part of the effort applied to the lever, so the lever delivers less output force than it would ideally. As a result, the mechanical advantage is reduced.

A pulley is a simple machine by which the direction of effort is changed to raise up a load.

In an ideal pulley, the effort applied is equal to the load to be lifted so it's mechanical advantage is 1.

A screw is a simple machine which appears like an inclined plane wound around a rod with a pointed tip. Hence, it appears like a nail with grooves on its circular curved surface. Examples : Car jack screw, bottle cap etc.

A wheel and axle is a simple machine made up of a wheel attached to a central rod (axle), where both rotate together. It helps in multiplying force to make work easier. Example : Steering wheel of a car, door knob.

The wheel acts as a force multiplier. When the wheel rotates, it turns the axle with it, resulting in linear motion. In a wheel-and-axle system, effort is usually applied to the larger wheel, while the smaller axle carries the load, making movement easier. The linear motion of the axle is obtained by rotating the wheel so as to reduce friction.

A wedge is a simple machine having a sharp edge which is formed by putting two inclined planes together. Example : Knife, axe etc.

(a) Beam balance : Class I lever

(b) Lemon crusher : Class II lever

(c) Sugar tongs : Class III lever

(d) Ramp : Inclined plane

(e) Door knob : Wheel and axle

(f) Needle : Wedge

To increase the life span of a machine following precautions must be followed :

1. We should keep the machines clean and free from dust.
2. If the parts of the machine are made of iron, they can rust. To prevent them from rusting, such parts must be painted.
3. Friction causes wear and tear of the moving parts of a machine. To reduce friction, these parts must be properly lubricated from time to time.

(a) Incorrect : A wheel barrow is a Class II lever.

(b) Incorrect : The efficiency of a machine is always less than 100%.

(c) Correct

(d) Incorrect : Class II levers have mechanical advantage greater than 1.

(e) Incorrect : It is easier to push a load along an inclined plane than to lift it vertically up.

(f) Incorrect : A wedge is made by two inclined planes placed together.

1. Lever → beam balance
2. Pulley → well pulley
3. Wheel and axle → steering wheel
4. Inclined plane → ramp
5. Wedge → nail
6. Screw → bottle cap

1. Lever of Class I : The lever in which the fulcrum is in between the load and the effort are called lever of class I. Generally, the effort arm of lever of class I is longer than the load arm, therefore, the mechanical advantage of a class I lever is greater than 1. However, if the effort arm is equal to the load arm, the mechanical advantage is equal to 1. But if the effort arm is shorter than the load arm, its mechanical advantage is less than 1. Thus, the mechanical advantage of a lever of class I can be greater than 1, equal to 1 or less than 1. Example : see-saw.

2. Lever of Class II : The lever in which the load is in between the fulcrum and the effort are called lever of class II. In class II lever, the fulcrum is at one end and the load is closer to the fulcrum. Thus, the effort arm is always longer than the load arm. Hence, the mechanical advantage of a class II lever is always more than 1. Example : nut cracker.

3. Lever of Class III : The lever in which the effort is in between the fulcrum and the load are called lever of class III. In class III lever, the fulcrum is at one end and the effort is close to the fulcrum, thus the effort arm is always shorter than the load arm. Hence, the mechanical advantage of a class III lever is always less than 1. Example : knife.

(a) See-saw is an example of class I lever in which the fulcrum is in between the load and the effort so that the effort arm is equal to the load arm.

(b) Beam balance is a type of class I lever in which the fulcrum is in between the load and the effort so that the effort arm is equal to the load arm.

(c) Nut cracker is an example of class II lever in which the fulcrum is at one end and the load is closer to the fulcrum. Thus, the effort arm is always longer than the load arm.

(d) Pair of forceps is a type of class III lever in which the effort is in between the fulcrum and the load so that the fulcrum is at one end and the effort is close to the fulcrum, thus the effort arm is always shorter than the load arm.

The mechanical advantage of an actual pulley is less than 1 due to friction present in pulley. The reason why we use the pulley when its mechanical advantage is equal to 1 or less than 1 is that the pulley allows us to apply the effort downwards i.e., in a convenient direction to raise the load.

The labelled diagram of a pulley being used to lift a load is given below :

In an ideal pulley, the effort applied is equal to the load to be lifted.

An inclined plane is a slanting wooden plank or a sloping surface. It is a simple machine which is used to move a load up with a less effort.

The effort required to push a load up an inclined plane is less than the load. Thus, the mechanical advantage of an inclined plane is always greater than 1.

Example :

1. Hospitals and huge buildings are provided with ramps which help nurses to move up the patients on a stretcher or to carry heavy equipments.

2. A coolie while loading a heavy drum on a truck uses a wooden plank. One end of the plank is kept on the edge of the truck and the other end on the ground. He then pushes the drum along the sloping surface and places it on the truck.

1. Machine makes work easier.
2. Friction force at the fulcrum reduces the mechanical advantage.
3. A wheel and axle is also a simple machine.
4. A pulley is a simple machine which is used for raising a load up by applying the effort downwards.
5. Screw driver is an example of wheel and axle.
6. Work is said to be done when a force applied on a body moves it.
7. Lever is a rod which can turn about a fixed point (fulcrum)

Given,

Effort = 10 kgf

Load = 100 kgf

Mechanical advantage of a machine is given by :

$$\begin{aligned}\text {Mechanical Advantage} =\frac{\text {Load}}{\text {Effort}} \\[1em] = \frac{100\ \text{kgf}}{10\ \text{kgf}}\\[1em] = 10\end{aligned}$$

So, the mechanical advantage of the machine is 10.

Given,

Mechanical advantage of the machine = 5

Effort = 2 kgf

As,

$$\begin{aligned}\text {Mechanical Advantage}=\frac{\text {Load}}{\text {Effort}}\\[1em] \Rightarrow \text {Load} = \text {Mechanical Advantage} \times \text {Effort} \\[1em] = 5\ \times 2 \text { kgf} \\[1em] = 10\text { kgf}\end{aligned}$$

Thus, the load can exert 10 kgf force for the effort of 2 kgf.

Given,

Mechanical advantage of the machine = 2

Load = 15 kgf

As,

$$\begin{aligned}\text {Mechanical Advantage}=\frac{\text {Load}}{\text {Effort}} \\[1em] \Rightarrow \text {Effort} = \frac{\text {Load}}{\text {Mechanical Advantage}} \\[1em] = \frac{15 \text{ kgf}}{2} \\[1em] = 7.5 \text{ kgf}\end{aligned}$$

Hence, to raise a load of 15 kgf, an effort of 7.5 kgf is needed.

Given,

Lever length = 100 cm

Effort = 15 kgf

Effort arm = 40 cm

Load arm = Lever length = 100 cm

Mechanical advantage of a lever is :

$$\begin{aligned}\text {Mechanical Advantage} = \frac{\text {Load}}{\text {Effort}} = \frac{\text {Effort Arm}}{\text {Load Arm}} \\[1em] \Rightarrow \text {Load} = \frac{\text {Effort Arm}}{\text {Load Arm}} \times \text {Effort} \\[1em] = \frac{40 \text { cm}}{100 \text { cm}} \times 15 \text { kgf}\\[1 em] = \frac{4}{10}\ \times 15 \text { kgf} \\[1em] = 6 \text { kgf}\end{aligned}$$

Thus, a load of 6 kgf should be applied for the effort of 15 kgf.

Given,

Distance of fulcrum from the load = 30 cm

Distance between load and effort = 90 cm

(a) Length of load arm = Distance of fulcrum from the load = 30 cm

(b) Length of effort arm = Distance between load and effort + Length of load arm

= 90 + 30

= 120 cm

(c) Mechanical advantage of a lever is :

$$\begin{aligned}\text {Mechanical Advantage} = \frac{\text {Effort Arm}}{\text {Load Arm}} \\[1em] = \frac{120 \text { cm}}{30 \text { cm}} \\[1em] = 4\end{aligned}$$

(i) The loading ramp is an inclined plane. It is used to raise heavy objects to a height with less effort.

(ii) The workers use a gentle sloping ramp because it requires less force to move the trays upwards. The smaller force has to be applied over a longer distance.

(iii) Yes. The loading ramp provides mechanical advantage because the effort required to raise the load is less than the load itself. A gentler and longer slope requires less effort.

(iv) A fishing rod is a Class III lever because the effort is applied between the fulcrum and the load.

(v) Yes. The length of a fishing rod makes a difference. If the position of the hands remains the same, a longer fishing rod has a longer load arm. Therefore, its mechanical advantage decreases and greater effort is required to handle the same load. However, the longer rod provides a greater reach.