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### Concept of force

• Concept of force is central to all of physics whether it is classical physics,nuclear physics,quantum physics or any other form of physics
• So what is force? when we push or pull anybody we are said to exert force on the body
• Push or pull applied on a body does not exactly define the force in general.We can define force as an influence causing a body at rest or moving with constant velocity to undergo an accleration
• There are many ways in which one body can exert force on another body
Few examples are given below
(a)Stretched springs exerts force on the bodies attached to its ends
(b)Compressed air in a container exerts force on the walls of the container
(c) Force can be used to deform a flexible object
There are lots of examples you could find looking around yourself
• Force of gravitational attraction exerted by earth is a kind of force that acts on every physical body on the earth and is called the weight of the body
• Mechanical and gravitation forces are not the only forces present infact all the forces in Universe are based on four fundamental forces
(i) Strong and weak forces: These are forces at very short distance (10-05 m) and are responsible for interaction between neutrons and proton in atomic nucleus
(ii) Electromagnetic forces: EM force acts between electric charges
(iii) Gravitational force -it acts between the masses
• In mechanics we will only study about the mechanical and gravitational forces
• Force is a vector quatity and it needs both the magnitude as well as direction for its complete description
• SI unit of force is Newton (N) and CGS unit is dyne where
1 dyne= 1005 N