Rain Drop Shape Dynamics

The shape of a falling rain drop is determined by a balance between surface tension and air resistance.

• Surface Tension: Acts to minimize the surface area, naturally pulling liquid into a spherical shape. This is dominant for very small drops.
• Air Resistance: As a drop falls faster, the pressure of the air pushing up against its bottom increases. This pressure difference flattens the drop.

Drop Size and Shape Effects

Rain drops are not perfectly spherical, especially larger ones. The size of the drop significantly influences its shape:

• Drops smaller than 1 mm in diameter are nearly spherical.
• Drops larger than 1 mm become increasingly flattened on the bottom due to air resistance. A 5 mm rain drop is large enough for this effect to be very pronounced.

5mm Rain Drop Shape

A rain drop with a diameter of 5 mm experiences significant air resistance. The air pressure pushing upwards on the bottom of the drop is much greater than the surface tension holding it together in a spherical form. This causes the bottom of the drop to flatten, and the drop takes on a shape resembling a hamburger bun or a parachute, wider than it is tall.

The image depicting this flattened, disc-like shape accurately represents a 5 mm rain drop falling through the atmosphere.