Common forces in mechanics :
(i) Weight : Weight of an object is the force with which earth attracts it. (W = mg)
(ii) Reaction or Normal force : When a body is placed on a rigid surface, the body experience a force which is perpendicular to the surfaces in contact. Then force is called ‘Normal force’ or ‘Reaction’.
(iii) Tension : The force exerted by the end of taut string, rope or chain against pulling (applied) force is called the tension. The direction of tension is so as to pull the body.
(iv) Spring force : Every spring resists any attempt to change its length. This resistive force increases with changes in length. Spring force is given by F = – Kx; where x is the change in length and K is the spring constant (unit N/m).
