# Notes on Simple Machine

**Notes on simple machine**

**MACHINES**

A machine is any device by means of which work can be done more conveniently.

**Mechanical Advantage (M.A.)**

The M.A. of a machine is defined as the ratio of load to the effort

Mechanical Advantage (M.A.) = load / effort

**Velocity Ratio (V.R.)**

The velocity ratio V.R. of a machine is defined as the distance moved by the effort to the distance moved by the load.

Velocity Ratio (V.R.) = distance moved by the effort / distance moved by the load

**Efficiency**

The efficiency of a machine is** the ratio of the useful work done by a machine to the total work put into the machine.**

i.e. Efficiency = ( workout / workinput)*100%

Also, **Efficiency **= (M.A /V.R)*100%

**THE LEVER**

**A lever is a simple machine. **It consists of a rigid body which is pivoted about a point called the fulcrum. The lever is based on the principle of moment. The V.R is the ratio of the two arms of the lever.

**1st class Lever**

The fulcrum (F) is between the load (L) and the effort (E). The velocity ratio is usually greater than 1 but could be less than or equal to 1.

Examples of First Order Lever are: See-saw, crowbar, claw hammer, pliers, a pair of scissors or pincers.

**2nd Class Lever **

The load is between the fulcrum and the effort. M.A and V.R are always greater than 1.

Examples of Second order lever are: nutcracker and wheelbarrow.

**3rd Class Lever**

** **The effort is between the fulcrum and the load. M.A and V.R are less than 1.

Examples of third order lever are: forearm, forceps, sugar tongs, and table knife.

**THE PULLEYS**

A pulley is a **wheel with a grooved rim**, and there can be several of these mounted in a framework called a block. The effort is applied to a rope which passes over the pulleys.

**THE BLOCK AND TACKLE**

The block and tackle is the type of pulley system used in cranes and lifts. It consists of two blocks each with one or more pulleys

In a block and tickle system the V.R is always equal to the total number of pulleys in the two blocks together.

**INCLINED PLANE**

A heavy load may be raised more easily by pulling it along a sloping surface than by lifting it vertically. If l is the length of the plane and h its height, then;

V.R = L /h

For a perfect inclined plane, Load x distance moved by load = Effort x distance moved by effort

In the right–angle triangle

V.R = 1 /Sin θ

**THE WHEEL AND AXLE**

**V.R** = **R / r = radius of wheel / radius of axle
**

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