Why freely falling raindrop falls with a uniform velocity but the motion of a freely falling object/body has a non-uniform velocity?

A freely falling body experiences accelerated motion under the influence of gravitational force. If the medium in which the body is moving is a viscous material medium, it exerts a viscous force on the body in the opposite direction of motion, proportional to its velocity.

Thus the body experiences two opposite forces:

1. Gravity, downward.

2. Viscous force due to drag, upward. (This force increases in magnitude until the velocity of the object increases because it is directly proportional to the velocity.)

Now, when an object is allowed to fall freely under the force of gravity, it accelerates towards the Earth's surface with an acceleration of 9.8m/sec, and this acceleration remains constant. Having an acceleration of 9.8m/sec means the velocity of the object changes by 9.8m/sec in every next one second.

It means when the object was at rest before its fall it had a velocity (0 m/s), after one sec it attains a velocity of 9.8m/sec, after one more second its velocity increases by again 9.8m/sec and now it becomes 19.6m/sec.

As the velocity of the free-falling body keeps increasing after every second. It will start to cover more and more distance in that same one-second time interval, and the viscous force wouldn't be much sufficient that it can balance the force of gravity. Therefore the motion of a freely falling body is a non-uniform motion.

Whereas, when the raindrops fall with increasing speed due to gravity, then the speed up viscous force due to air also get increased. Eventually, the viscous force due to air is sufficient to balance the force of gravity, so the acceleration stops and the raindrop reaches a uniform or constant terminal velocity.


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