JSS 2: Simple machine (II)

             Mechanical Advantage (M.A)

Mechanical advantage or force ratio is the ability of a machine to overcome a large load through a small effort.

M.A has no S.I. unit 

Example: A load of 20N is raised by an effort of 4N. Calculate its mechanical advantage.

Solution: 

Mechanical advantage = Load/Effort

M.A = 20/4 

M.A = 5 

                       Velocity ratio (V.R)

Velocity ratio is the ratio of the distance moved by the effort to the distance moved by the load at the same time interval.

V.R has no S.I. unit 

Example: Calculate the velocity ratio of a machine if the distance moved by effort is 5m and that of the load is 2m.

Solution: 

V.R = distance moved by the effort/ distance moved by the load 

V.R = 5/2 

V.R = 2.5 

               Efficiency of a machine 

Work output: Work output is the useful work done by the machine 

Work input: Work input is the work done on the machine by the effort.

Efficiency is expressed in percentage (%)

A perfect or ideal machine has a 100% efficiency. This means that all the work done by the effort is completely used to overcome the load.

In practice, the efficiency of a machine is usually less than 100% because of friction in the moving parts of the machine.

Example: The mechanical advantage of a machine is 3. Calculate the efficiency. Given that its velocity ratio is 4.

Solution: 

Efficiency = (M.A / V.R.) x 100%

Efficiency = 3/4 x 100%

Efficiency = 0. 75 x 100%

Efficiency = 75%