Physical Science:

Gravitational force or Force of Gravity: The gravitational force exists due to the mass of an object. Gravitational force is the weakest known forces in nature. It is a long range force. It holds all the planets together. We discuss this force later in this section. This force is acting on any object due to attraction of earth. Near the surface of the earth force of gravity is given by its weight, i.e., Foece, \(F\) = weight = \(mg\text{.}\) Where g is the acceleration due to gravity and the direction force is acting along the center of the earth. Weight: It is the force acting on an object due to gravitational acceleration. Weight is the effect of force of gravity on an object located at a particular point. One kg of mass has a weight of about 10 N (\(F = 1 kg\times 9.8 m/s^2 \approx 10N\)).

Electromagnetic force: The electromagnetic force exists due to the charge in the object. It is also a long range force but stronger than the gravitational force. It holds all the atoms and molecules together. We discuss this force later in another chapter.

Strong nucleur force: The strong nucleur force is a short range force and it exists only inside the nucleus. It binds all the nucleons together to have atomic existance. It is the strongest force in nature.

Weak nuclear force: The weak nucleur force is also short range force and only exists inside the nucleus. It is weaker than strong nuclear force and electromagnetic force. It is responsible for radioactivity of nucleous. The improper ratio of nucleons may cause the weak nuclear force to exist.