The force of attraction of earth on bodies, is called force of gravity. Acceleration produced in the body by the force of gravity, is called acceleration due to gravity. It is represented by the symbol g.

In the absence of air resistance, it is found that all bodies (irrespective of the size, weight or composition) fall with the same acceleration near the surface of the earth. This motion of a body falling towards the earth from a small altitude (h << R) is called free fall.

We neglect air friction unless mentioned

We can use equations of Motion for solving Problems

Some cases are considered below.

Case 1: If a body dropped from some height (initial velocity zero)

                     u = 0            [As body starts from rest]

                     a = +g       [As acceleration is in the direction of motion]

                     v = g t                                     …(i)

                       h =( ½)gt²            …(ii)

                       v²=0+2gh             …(iii)

                     s_n=(g/2)(2n-1)   ...(iv)

 

Case 2. If a body is projected vertically downward with some initial velocity

Equation of motion :           v= u+ at

                   h=ut+ (1/2)gt²

                   v²=u²+2gh

                  s_n=u +(g/2)(2n-1)

Case 3. If a body is projected vertically upward

v= u- at

h=ut - (1/2)gt²

v²=u²-2gh

s_n=u -(g/2)(2n-1)