Definition:

         A machine is a device use to work with ease. We have two types of machines namely simple machines and compound machines. Simple machines include an eating spoon, pulley, lever, inclined plane.

         Compound machines include computer, grinding mill, helicopters, and plane and air craft.

TERMS ASSOCIATED TO MACHINES

1°) Mechanical Advantage (MA)

   Mechanical advantage is defined as the ratio of load to effort or it is the number of times the machine multiplies the effort. MA can be calculated from the formula below;

Mechanical Advantage= LoadEffort

MA= LE

 Mechanical advantage has no unit because it is a ratio.

Example: An effort of 500N is required to raise a load of 1000N onto a platform. Calculate the MA of the machine.

Solution

MA= LE                    But L = 1000N and E = 500N

MA= 1000500=2  

2°) Velocity Ratio (VR)

Velocity ratio is defined as the ratio of distance moved by effort to distance moved by load. It can be calculated by the formula below;

Velocity Ratio(VR)= Distance moved by effort(SE)Distance moved by loadSL

VR= SESL

Velocity ratio has no unit because it is a ratio.

3°) Efficiency (Ω)

Efficiency is defined as the ratio of work output to work input expressed as a percentage. It is also defined as the energy output to the energy input express as a percentage. Efficiency can be calculated from the formula below;

Efficiency(Ω)= Work outputWork input*100

Efficiency(Ω)= Energy outputEnergy input*100

Efficiency(Ω)= Power outputPower input*100

Why is the efficiency of a machine always less than 100%?

19. Work is done against the movable part of the machine. I.e. Work is done to overcome friction force.
19. Work is done in raising the lower blocks.

The Pulley System

The velocity ratio of a pulley system is obtained by counting the number of wheels or by counting the number of ropes midway the pulley. The velocity ratio of the single fixed is

Lever:

The lever is a bar which is free to rotate at a fixed point is called the pivot. Depending on the relative position of pivot, load and effort we have three types of levers namely;

First class, second class and third class.

• First Class Lever: With the first class lever, the pivot is situated between lo ad and effort.

• Second Class Lever: With the second, the load is between pivot and effort. Eg: wheel barrow, beer opener.

• Third Class Lever: With the third class lever, the effort is between load and pivot. Eg: Sugar tong.

The Inclined Plane

MA= LE= mgmg sinθ= 1sinθ                       VR=LN= LLsinθ=1sinθ

For an inclined plane, MA equals VR. i.e. MA=VR= 1sinθ