First Class Lever

A first-class lever has the fulcrum/pivot in the middle and the load and effort on each side of the fulcrum.

Examples of a first class lever

Pliers, scissors, a crow bar, a claw hammer, a see-saw and a weighing balance.

Second Class Lever

In second class levers the load is between the effort (force) and the fulcrum. A common example is a wheelbarrow where the effort moves a large distance to lift a heavy load, with the axle and wheel as the fulcrum.

Nutcrackers are also an example of a second class lever.

Third Class Lever

With third class levers the effort is between the load and the fulcrum, for example in barbecue tongs. Other examples of third class levers are a broom, a fishing rod, etc.

First Class Lever

A first-class lever has the fulcrum/pivot in the middle and the load and effort on each side of the fulcrum.

Examples of a first class lever

Pliers, scissors, a crow bar, a claw hammer, a see-saw and a weighing balance.

Second Class Lever

In second class levers the load is between the effort (force) and the fulcrum. A common example is a wheelbarrow where the effort moves a large distance to lift a heavy load, with the axle and wheel as the fulcrum.

Nutcrackers are also an example of a second class lever.

Third Class Lever

With third class levers the effort is between the load and the fulcrum, for example in barbecue tongs. Other examples of third class levers are a broom, a fishing rod, etc.

Work = Force x Distance

Force = 100 N
Distance = 2 m

Work = 100 x 2 = 200 J

Force = 100 N
Distance = 2 m

Work = 100 x 2 = 200 J

Time = 10 s

Power = $\frac{\mathrm{200\; J}}{\mathrm{10\; s}}$ = 20 Js^-1 = 20 W

A complex machine is a combination of two or more simple machines. Examples: Tractors, Cars, Mist blower, Sewing machines & Mower

Work = Force x Distance

If there is no movement (distance = 0), work is also 0.

Thus when distance = 0,

Work done = Force x 0 = 0 J

Work done = Force x Distance

Force = 2.5 N

2.5 = $\frac{25}{10}$

Distance = 4 m

Work done = 2.5 x 4 = $\frac{25}{10}$ x 4 = 10 J

Note:
1. 2 divides 4, 2 times and 10, 5 times
2. 5 divides itself 1 time and 25, 5 times
3. 5 x 2 = 10
4. The unit of work done is Joule (J)

Alternatively

2.5 = 2.⌒5. = 25 x 10^-1

2.5 x 4 = 25 x 10^-1 x 4

2.5 x 4 = 25 x 4 x 10^-1

2.5 x 4 = 100 x 10^-1

100 = 10 x 10 = 10^{1 + 1} = 10²

2.5 x 4 = 10² x 10^-1

Law of multiplication of indices

a^m x aⁿ = a^{m + m}

2.5 x 4 = 10^{2 + -1}

2.5 x 4 = 10^{2 - 1}

2.5 x 4 = 10¹

Any number raised to the power 1 is the same number.

2.5 x 4 = 10

Work done = Force x Distance

Force = 40 N

Distance = 10 m

Work done = 40 N x 10 m = 400 J

Work done = Force x Distance

When there is no movement, distance = 0

Work done = Force x 0 = 0 J

Work done = Force x Distance

Force = Weight = 40 N

Distance = 1 m

Work done = 40 N x 1 m = 40 J

Work done = Force x Distance

Distance = $\frac{\mathrm{Work\; done}}{\mathrm{Force}}$

Work done = 80.0 J

Force = 40.0 N

Distance = $\frac{\mathrm{80.0\; J}}{\mathrm{40.0\; N}}$ = 2 m

Work done = Force x Distance

Force = 20.0 N

Distance = 10.0 cm

The S.I unit of distance is metre. Hence convert the 10.0 cm to metre by dividing by 100

10 cm = $\frac{10}{100}$ m

Work done = 20 N x $\frac{10}{100}$ m = 2 J

Notes:

1. 20 divides itself 1 time and 100, 5 times

2. 5 divides itself 1 time and 10, 2 times

Efficiency of a machine = $\frac{\mathrm{Work/Energy\; Output}}{\mathrm{Work/Energy\; Input}}$ x 100%

Work/Energy output = Work/Energy input - Energy Lost

Work/Energy output = 600 J - 200 J

Work/Energy output = 400 J

Efficiency of a machine = $\frac{\mathrm{400\; J}}{\mathrm{600\; J}}$ x 100% = 66.67% ≈ 67%

Work done = Force x Distance

Force = 20 N

Distance = 2 m

Work done = 20 N x 2 m = 40 J

Work done = Force x Distance

Force = Weight = 60 N

Distance = 2 m

Work done = 60 N x 2 m = 120 J

Work done = Force x Distance
Force = 50 N
Distance = 6 m

Work done = 50 x 6 = 300 J

Work done = Force x Distance

For work to be done, force must be applied and distance must be covered.

When at a fixed position, distance covered is 0 hence work done will be 0 even when force is applied to a load at a fixed position.

Efficiency = 100% - % Energy Loss
Efficiency = 100% - 10%
Efficiency = 90%

First class → Pivot/Fulcrum at the middle
Second class → Load at the middle
Third class → Effort at the middle

In summary PLE which is the last three letters of PEOPLE if you may forget in an examination.

Work done = Force x Distance

Divide both sides by Force

Distance = $\frac{\mathrm{Work\; done}}{\mathrm{Force}}$

Distance = $\frac{75}{50}$ = 1.5 m

Mechanical Advantage = $\frac{\mathrm{Effort\; Distance}}{\mathrm{Load\; Distance}}$

Load Distance: is the distance between the pivot (fulcrum) and the load
Effort Distance: Is the distance between the pivot (fulcrum) and the effort

Since the effort distance is the numerator in the mechanical advantage formula, the greater it is than the load distance, the greater the mechanical advantage and the better the efficiency of the machine/lever.

First class → Pivot/Fulcrum at the middle
Second class → Load at the middle
Third class → Effort at the middle

In summary PLE which is the last three letters of PEOPLE if you may forget in an examination.

Work done = Force x Distance

Work done = 720 J
Distance = 12 m

720 = Force x 12

Divide both sides by 12

Force = $\frac{720}{12}$ = 60 N

Work done = Force x Distance moved
Force = 2N
Distance = 10 m
Work done = 2 N x 10 m
Work done = 20 J

Load Distance: is the distance between the pivot (fulcrum) and the load
Effort Distance: Is the distance between the pivot (fulcrum) and the effort

Mechanical Advantage = $\frac{\mathrm{Effort\; Distance}}{\mathrm{Load\; Distance}}$

Load Distance: is the distance between the pivot (fulcrum) and the load
Effort Distance: Is the distance between the pivot (fulcrum) and the effort

Since the effort distance (Y) is the numerator in the mechanical advantage formula, the greater it is than the load distance (X), the greater the mechanical advantage and the better the efficiency of the machine/lever.

Screw

A screw is an inclined plane that is coiled around a shaft. They usually have one flat end and one pointed end.

Power = $\frac{\mathrm{Work\; done}}{\mathrm{Time}}$

Forceps

Friction reduces the efficiency of the machine as part of the work input is used to overcome friction. Oiling the parts reduces the friction thereby increasing the efficiency of the machine.

The mechanical advantage of a lever can be calculated as shown below:

The higher the mechanical advantage, the better the machine our work output.

From the formula you will realize that the longer the distance of the effort from the pivot, the higher the mechanical advantage will be since the distance from the load and pivot is fixed (constant).

The distance P will have the highest mechanical advantage, hence that is the best position to apply the force to lift the load.

Work done = Force x Distance
Force = 10 N
Distance = 2 m
Work done = 10 N x 2 m
Work done = 20 J

Work done = Force x Distance

Distance = $\frac{\mathrm{Work\; done}}{\mathrm{Force}}$

Work done = 60 J

Force = 20 N

Distance = $\frac{60}{20}$ = 3 m

Note: Energy output/input is the same as work output/input

Energy output = 40 J
Efficiency = 50%

Energy input = $\frac{\mathrm{40\; J}}{\mathrm{50\%}}$ x 100% = 40 x 2 = 80 J