Force

'To push' or 'Pull' any object is called force. Means it creates change in position of any object.

Properties of force -

1. It will be in point form.
2. Due to force the shape, size and mass will change.
3. No any contact required for apply force.
4. When multiple force applied on any object. Object is in rest then it is condition of equilibrium. In this condition total force on object is zero.
5. When multiple force applied on any object. Object is not in rest then it is condition of non-equilibrium. Object moves in the direction of resulting force.
6. When force applied perpendicular to the direction of motion of object. Object moves in elliptical path.
7. When force applied perpendicular to the direction of motion of object at every point of motion. Object moves in circular path.

Fundamental forces are following -

1. Gravitational force - Every object which have mass attract another object of mass.
It is the weakest force in nature. 

Its range is very high.
It is given by Newton.
According to Newton's universal law of gravity - "The force between two objects is directly proportional to product of their masses and inversely proportional to square of distance between them.
If two objects of masses M1 & M2 placed R distance apart then
F ∝ M1 M2
F ∝ 1/R^2
F ∝ (M1 M2)/R^2
So F = G(M1 M2)/R^2
Unit of force is Newton, denoted by N.
Here G is gravitational constant.

G = F.R^2/(M1 M2)
  =N.m^2/kg^2
For earth G= 6.67*10^(-11) Nm^2/kg^2

2. Electromagnetic force - When constant electric current flow in circuit then magnetic field generate around it.

It is second strongest force in nature.

3. Strong nuclear force - It is applied between nucleons(neutron, proton). It is high attracting force which bind nucleons.
It is the strongest force in nature.

4. Weak nuclear force - It is due to ß decay from nucleus. Then that nucleus attract nearby nucleus.