Free fall :
- Force of gravity due to the earth acts on each and every object.
- Whenever an object moves under the influence of the force of gravity alone, it is said to be falling freely.
- In free fall, the initial velocity of the object is zero and goes on increasing due to the acceleration due to gravity of the earth.
- During free fall, the frictional force due to air opposes the motion of the object and a buoyant force also acts on the object.
- Thus, true free fall is possible only in vacuum.
- For a freely falling object, the velocity on reaching the earth and the time taken for it can be calculated by using Newton’s equations of motion.
- For free fall, the initial velocity u = 0 and the acceleration a = g. Thus we can write the equations as
s = ½ gt
v² = 2gs
- For calculating the motion of an object thrown upwards, acceleration is negative, i.e. in a direction opposite to the velocity and is taken to be – g.
- The magnitude of g is the same but the velocity of the object decreases because of this -ve acceleration.
- The moon and the artificial satellites are moving only under the influence of the gravitational field of the earth. Thus they are in free fall.
Galileo Experiment :
- When we drop a feather and a heavy stone at the same time from a height, they do not reach the earth at the same time.
- The feather experiences a buoyant force and a frictional force due to air and therefore floats and reaches the ground slowly, later than the heavy stone.
- The buoyant and frictional forces on the stone are much less than the weight of the stone and does not affect the speed of the stone much.
- Recently, scientists performed this experiment in vacuum and showed that the feather and stone indeed reach the earth at the same time.