Concept Of Simple Machines

Machine is any device, which is used for simplifying work. Examples of machines are: a crowbar, a seesaw, a claw hammer, a pulley and an inclined plane. 

Types of machine:

There are two types of machines

1.       Simple machine

2.       Complex machine

Simple machine

What is simple machine?

Simple machine is any device, which requires single force in operation to simplify work e.g. Claw – hammer, a pulley, and an inclined plane.

In a simple machine, a force is applied at one convenient point to overcome another force acting at another point.

Claw bar.

The diagram above shows a stone being shifted. Force is applied at one end of the bar in order to exert an upward force on the stone. The down ward force is called effort and the weight of the stone is called load.

Effort is the force used to operate a machine.
                        and
Load is the resistance, which machines overcome.

Terms used in simple machine

Mechanical advantage (M.A)

 Is the ratio of load and effort.

Mathematically:

Mechanical advantage has no SI unit.

Example 1:

A simple machine raises a load of 100N by using a force 50N. Calculate the mechanical advantage.
 Solution;

 Data given

Mechanical advantage = 2

Example 2.

A force of 20N raises a load of 100kg. Calculate mechanical advantage of the machine.

Solution;
Data given ;

Mechanical Advantage = 50

Velocity ratio (V.R)

Velocity ratio is the ratio of distance traveled by effort and distance traveled by load.
                   Or
Velocity ratio is the distance moved by effort per distance moved by load.

Example

In a certain machine a force of 10N moves down a distance of 5cm in order to raise a load of 100N through a height of 0.5cm calculated the velocity ratio (V.R) of the machine.

Solution:

Data given

Distance by Effort = 5cm
Distance moved by load = 0.5cm

The velocity ratio (V.R) of the machine = 10

Efficiency of machine

Efficiency of machine is the ratio of work output and work input.

Work output = Load x Distance moved by Load

Work input = Effort x Distance moved by Effort

A perfect machine has 100% Efficiency. Therefore, M.A is equal to V.R.

Note: most machines are imperfect machines since efficiency is less than 100% this is due to the friction and heat and loss of energy.

Example1:

A certain machine with force of 10N moves down a distance of 5cm in order to raise a load of 100N through a height of 0.5cm.

Calculate:    (i) M.A
                     (ii) V.R

                     (iii) Efficiency of machine

Solution:

Date given:
Effort = 10N
Load = 100N

Distance moved by effort = 5cm
Distance of load= 0.5cm
Efficiency machine?

Efficiency of machine (£) = M.A  x 100%

The velocity ratio = 10

Efficiency of the machine = 100%