machine It is a device that transmits force from one point to another, changing its magnitude and direction. The basic machines are the lever, the inclined plane, and the hydraulic press. All other machines are developments of these basic machines.

Actual mechanical advantage (AMA) of a machine is defined as the ratio of output force, F_out to the input force F_in.

Actual mechanical advantage (AMA) = F_out / F_in

Theoretical mechanical advantage (TMA), is the mechanical advantage without friction. It is given by,

Theoretical mechanical advantage (TMA) = d_in / d_out

where d_in and d_out respectively are the distances through which the input and output forces act.

Efficiency of a machine is defined as,

Efficiency = work output / work input

= AMA / TMA

= power output / power input

Fig.m1 shows the lever. The TMA of the machine is given by,

TMA = L_in / L_out

The wheel and axle (fig. m2), belt and gear drives (fig. m3) and pulley systems are all developments of the lever.

Belt and gear drives (fig. m3) transmit torque from one shaft to another. The actual mechanical advantage of any such system is,

AMA = output torque / input torque

The theoretical mechanical advantage of a pulley system equals the ratio between the radius of the driven pulley, r_out and that of the driving pulley, r_in .

TMA = r_out / r_in

In case of a gear drive, since the number of teeth on a gear is proportional to radius,

TMA = no. of teeth on driven gear/ no. of teeth on the driving gear

In any torque transmission system, the angular velocity ratio is the inverse of the TMA.

TMA^-1 = output angular velocity / input angular velocity

For an inclined plane (fig. m4) the theoretical mechanical advantage is given by,

TMA = L/ h

Wedges and screws are developments of the inclined plane.