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Free Fall

An object is said to have a free fall when it falls vertically under the influence of gravity alone, free from air resistance.

A free-falling object is an object which falls under the sole influence of gravity. Thus, any object which is moving and being acted upon only by the force of gravity is said to be "in a state of free fall." We know that an object experiences acceleration during free fall. This definition of free fall leads to two important characteristics about a free-falling object:

  • Free-falling objects do not encounter air resistance.
  • All free-falling objects (on Earth) accelerate downwards at a rate of 9.8 m/s-2 (approximately 10 m/s-2).

Free-fall is independent of mass of the object. This means that all objects big or small should fall at the same rate. This free-fall acceleration can also be demonstrated using a strobe light and a stream of dripping water. If water dripping from a medicine dropper is illuminated with a strobe light and the strobe light is adjusted such that the stream of water is illuminated at a regular rate – say every 0.2 seconds; instead of seeing a stream of water free-falling from the medicine dropper, you will see several consecutive drops. These drops will not be equally spaced apart; instead the spacing increases with the time of fall (as shown in the diagram above), a fact which serves to illustrate the nature of free-fall acceleration.

Assuming that the position of a free-falling ball dropped from a position of rest is shown every 1 second, the velocity of the ball will be shown to increase as depicted in the diagram at the left.


This diagram is not drawn to scale – it would take no more than two seconds for a ball to drop from shoulder height to toe height

So the acceleration 'a' is replaced by 'g'.

v = u + at

s = ut + at2/2

v2 = u2 + 2as

We will take acceleration to be positive, when the object moves towards the earth and it is negative when it moves away (against) from the earth.


Examples :

i) Fruits like ripe mangoes falling from a tree.

ii) A skydiver with an unopened parachute.

iii) A bungee jumper.



Galileo Galilei



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