A simple mechanical machine is a device that changes the direction or/and magnitude of a force. A simple machine can be defined as the most simple mechanism which can provide mechanical advantage.
The forces acting on simple mechanical machines can be divided into:
For a mechanical machine in equilibrium, the mechanical advantage is defined as the ratio of the effort force and resistant. Mathematically it is:$$VM = \frac{\Gamma}{R}.$$
The lever is a rigid bar which can rotate around an axis in which it is supported. The rotation axis of a lever is called fulcrum.
The equilibrium condition for any lever is: $$ R \times B = \Gamma \times b,$$ where \(B\) is the force of the resilient arm and \(b\) is the effort arm of force.
The pulley is used to transfer force and motion. A pulley is composed of a rigid material wheel which rotates on a shaft driven by a belt or rope.
It is a rigid plane, in this given example frictionless and inclined of an angle \(\theta\) (see drawings above). The equilibrium condition for this machine is: $$ \Gamma = P sen(\theta). $$ Examples of machines that use the principle of the inclined plane: screw, jack screw and wedge.