There are many different type of force and some of them have the same origin – the electric force. The following table provides a summary.
Name of force | Description |
Gravitational | The force between objects of mass |
Electrostatic force | The force between objects separated by a distance r as a result of their electric charges |
Magnetic force | The force between magnets/currents |
Normal reaction | The force between surfaces in contact. The normal reaction force is always at rightangles to the point of contact. If the surfaces are smooth, it is the only force between them. |
Friction | The forces that oppose the sliding of surfaces in contact past each other. Acts along the surfaces. Air resistance can be thought of as friction. |
Tension | When a string is stretched, a tension is produced in the string, always acting towards the centre of the string. When the string is attached to an object it will exert a force on the object equal to the tension. |
Compression | When a rod is compressed, it experiences a force pushing the ends of the rod inwards. A force is produced opposing further compression. If the ends of the rod are put in contact with another object, they exert a force equal to the compressive force. |
Upthrust | The force that acts on an object submerged in a fluid. It is equal to the weight of fluid displaced by Archimedes principle and acts upwards. |
Lift | The force produced on an object when a fluid flows over it in an asymmetrical way. The shape of an aircraft wing causes lift which enables the aircraft to fly. |
and 
separated by a distance
as a result of their masses, also called the weight in the gravitational field of the other. Given by the equation
- the – indicates an attractive force, in the direction of r decreasing.
and
given by
The force is repulsive, in direction of increasing
of like sign and attractive for unlike charges.