Raindrop

Let's take a look!

Watch the video on YouTube.

What kind of experiment is this?

Experimental procedure and explanation:

• Let’s think about the speed of a raindrop. Aerodynamic resistance acts on any object falling through the air. In the beginning, the object accelerates, but after a certain distance, it reaches a speed called the “terminal velocity” and maintains the speed from that point onward.
• In this experiment, we verify that a raindrop floats when its terminal velocity coincides with the upward blowing air speed.
• We learn in high school physics that when air resistance can be ignored, an object falls with a constant acceleration. When observing the free fall of a heavy object over a limited distance, ignoring air resistance does not make much difference to the actual phenomena.
• However, when a raindrop falls from the sky, air resistance cannot be ignored.
  In most cases, air resistance is proportional to the square of the speed. This applies to raindrops as well. (Air resistance is nearly proportional to the speed in very special circumstances, such as when the object is extremely small or light.)
• A falling raindrop initially accelerates due to the gravitational force, while air resistance increases roughly proportional to the square of the velocity. However, when the magnitude of the air resistance equals the gravitational force, the speed no longer increases and the raindrops falls at a constant velocity, called the “terminal velocity.”

[Keywords]	Air resistance, Terminal velocity
[Related items]	Parachute, Heavy Ball and Light Ball, Large Ball and Small Ball
[Reference]	“Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, pp. 76–77.