Mechanical Advantage

Mechanisms are often used to allow a small effort to move a large load. For example, a car jack allows an average person to lift a car which may weigh as much as 2000kg whilst exerting only a force equivalent to 10 or 20kg.

This property of mechanisms is known as Mechanical Advantage (MA), and for any particular system, has a specific numerical value. The Mechanical Advantage of a system is calculated by dividing the load by the effort.

In an ideal world, the Mechanical Advantage of a mechanical system would be numerically equivalent to its Velocity Ratio - i.e. we ‘pay’ for being able to raise a large load by applying effort over a large distance. Machines are not 100% efficient however, there are losses due to wear and tear, friction, heat and noise for example, and so we do not ‘get out’ quite as much as we ‘put in’. The Efficency (or inefficiency!) of a mechanical system can therefore be calculated by dividing its Mechanical Advantage (MA) by its Velocity Ratio (VR) and then multiplying by 100 to get a percentage - i.e. Efficiency = MA/VR x 100%