Why are raindrops shaped like pear instead of a ball?

Raindrops are spherical when they begin to fall from the cloud, but as they encounter air resistance, their shape changes to an oblate spheroid with flattened faces. This shape is sometimes referred to as "tear-drop" or "pear-drop," even though it is actually more of an ellipsoid like an American football.

A number of factors contribute to this change in shape:

* Viscosity: Water has a relatively high viscosity, which means that it resists flow. This means that the water on the outside of the drop slows down as it encounters air resistance, while the water on the inside continues to move at a higher speed. The resulting shear force causes the drop to flatten.

* Gravitational force: The force of gravity pulls down on the raindrop, causing it to be flattened in the vertical direction.

* Surface tension: Water has a relatively high surface tension, which means that its surface molecules tend to stick together. This surface tension helps to support the weight of the raindrop and prevents it from breaking apart.

The size of a raindrop also plays a role in its shape. Smaller raindrops are more spherical than larger raindrops, because they experience less air resistance.

The average size of a raindrop is about 1-2 mm in diameter. This size range is large enough to experience significant air resistance, but small enough to be supported by surface tension.