why raindrops doesnt kill?

Answer 1

It a liquid, and the speed is not enough to hurt a human being expect it an acid rain.

rain can be divided into:[1]

very light rain — when the precipitation rate is < 0.25 mm/hour
light rain — when the precipitation rate is between 0.25 mm/hour - 1.0mm/hour
moderate rain — when the precipitation rate is between 1.0 mm/hour - 4.0mm/hour
heavy rain — when the precipitation rate is between 4.0 mm/hour - 16.0mm/hour
very heavy rain — when the precipitation rate is between 16.0 mm/hour - 50mm/hour
extreme rain — when the precipitation rate is > 50.0 mm/hour

Answer 2

A raindrop doesn't kill you because it is not moving at a very great velocity. A raindrop falls from high enough to achieve its terminal velocity, which means that it is no longer accelerating. And a raindrop just doesn't have a particularly large terminal velocity--only 5 to 20 mph, compared with 125 mph for a falling human.

If you want to get very technical, you can calculate the force from each raindrop. The force of an impinging fluid is F = p(v^2)A, where p is density, v is velocity, and A is cross-sectional area. p for water is 1000 kg/m^3, v in SI units is 9 m/s (for 20 mph), and the diameter of the raindrop is given in my first reference as 5 mm for a cross-sectional area of pi*0.0025^2 = 0.000020 m^2. So F = p(v^2)A = (1000)(9^2)(0.000020) = 1.59 N, which is the same as the force you experience from an 0.16 kg mass sitting on your head.

The pressure associated with an impinging fluid is just pv^2, which here would be 81 kPa. Atmospheric pressure is 101 kPa, so the falling rain can again be seen to be relatively inconsequential and harmless.

Answer 3

Because there isn't enough water in one raindrop to drown a person.