Non-contact force

A non-contact force is a force applied to an object by another body that is not in direct contact with it. The most familiar example of a non-contact force is gravity. In contrast a contact force is a force applied to a body by another body that is in contact with it. However it is to be noted that the origin of all contact forces (such as, for example, friction) can be traced to non-contact forces.

The four known fundamental interactions are all non-contact forces:

• Gravity, a non-contact force between an two objects, and related to the concept of mass. The force exerted on each body by the other through weight is proportional to the mass of the first body times the mass of the second body divided by the square of the distance between them. The direction of the force is from the body acted on towards the body applying the force. A human body's weight is a non-contact force exerted by the Earth on their mass.

• Electromagnetism is the force that causes the interaction between electrically charged particles; the areas in which this happens are called electromagnetic fields. Examples of this force include: electricity, magnetism, radio waves, microwaves, infrared, visible light, X-rays and gamma rays.

• Strong nuclear force: Unlike Gravity and electromagnetism, the strong nuclear force is a short distance force that takes place between fundamental particles within a nucleus. It is charge independent and acts equally between a proton and a proton, a neutron and a neutron, and a proton and a neutron. The strong nuclear force is the strongest force in nature; however, its range is small (acting only over distances of the order of 10⁻¹⁵ m).

• Weak nuclear force: The weak nuclear force appears only in certain nuclear processes like β decay of a nucleus, in which the nucleus emits a β particle and an uncharged particle called a neutrino. Both the strong and weak forces form an important part of quantum mechanics.