Leavers

Levers

A lever is a rigid body that turns about a fixed point known as the fulcrum or pivot. It is commonly used to shift or lift heavy loads by applying an effort force.

Classes of levers

There are three main classes of levers, which are categorized based on the relative positions of the Load (L), Effort (E), and Fulcrum (F):

i. First class lever

In this type of lever, the Fulcrum is positioned between the Load and the Effort.

Arrangement: $\text{Effort} \quad \longrightarrow \quad \text{Fulcrum} \quad \longrightarrow \quad \text{Load}$

Examples: Seesaw, crowbar, pair of scissors, claw hammer.

The mechanical advantage (M.A) for a lever is calculated by:

$$\text{M.A} = \frac{\text{Load}}{\text{Effort}}$$

The velocity ratio (V.R) for a lever is:

$$\text{V.R} = \frac{\text{Distance from Effort to Fulcrum}}{\text{Distance from Load to Fulcrum}}$$

ii. Second class lever

A Second Class Lever is the type of lever in which the Load (L) is positioned between the Fulcrum (F) and the Effort (E).

Arrangement: $\text{Fulcrum} \quad \longrightarrow \quad \text{Load} \quad \longrightarrow \quad \text{Effort}$

In this setup, a small effort can be used to move a large load, giving the lever a mechanical advantage.

Examples: Wheelbarrow, nutcracker, bottle opener, tongs (with correct configuration).

Mechanical Advantage (M.A):

$$\text{M.A} = \frac{\text{Load}}{\text{Effort}}$$

Velocity Ratio (V.R):

$$\text{V.R} = \frac{\text{Distance from Effort to Fulcrum}}{\text{Distance from Load to Fulcrum}}$$

Note: Second class levers always have a mechanical advantage greater than 1, meaning they multiply force.

Second Class Lever

iii. Third class lever

A Third Class Lever is the type of lever in which the Effort (E) is applied between the Fulcrum (F) and the Load (L).

Arrangement: $\text{Fulcrum} \quad \longrightarrow \quad \text{Effort} \quad \longrightarrow \quad \text{Load}$

This lever does not provide a mechanical advantage in terms of multiplying force, but it is useful in increasing speed and distance of movement.

Examples: Fishing rod, human arm lifting a weight, tweezers, broom.

Mechanical Advantage (M.A):

$$\text{M.A} = \frac{\text{Load}}{\text{Effort}} \lt 1$$

Velocity Ratio (V.R):

$$\text{V.R} = \frac{\text{Distance from Effort to Fulcrum}}{\text{Distance from Load to Fulcrum}}$$

Note: Third class levers usually require more effort than load, but they are ideal for tasks needing greater control or speed.

Third Class Lever

Use of levers in daily life

1. Lifting heavy objects with a crowbar (First Class Lever); A crowbar acts as a lever to multiply the force applied by a person, making it easier to lift or move heavy stones or nails. The fulcrum is placed under the bar, and a small effort can lift a heavy load.
2. Cutting materials using scissors (First Class Lever); Scissors use two first class levers connected at a fulcrum (the screw in the middle). Effort is applied at the handles, and the cutting force is applied at the blades, allowing us to cut paper or fabric with ease.
3. Carrying loads in a wheelbarrow (Second Class Lever); In a wheelbarrow, the load is placed between the wheel (fulcrum) and the handles (where the effort is applied). This allows a user to lift and transport heavy materials like soil or bricks with less force.
4. Lifting a person using a seesaw (First Class Lever); A seesaw or teeter-totter is a classic example of a first class lever where the fulcrum is in the middle. Two people balance each other by adjusting their positions and weights to move up and down.
5. Using a broom to sweep (Third Class Lever); In a broom, your top hand acts as the fulcrum, the effort is applied in the middle, and the load is the resistance of the floor. This allows fast sweeping motion over a wide area.
6. Using a fishing rod (Third Class Lever); The hand holding the rod acts as the fulcrum, effort is applied near the middle, and the load is the weight of the fish. This lever increases the speed and distance of the rod tip, making casting easier.