Question

Rain drops are spherical in shape because of

• A. surface tension
• B. capillary
• C. downward motion
• D. acceleration due to gravity

Hint:

Surface tension is nature's way of minimizing surface area.
Whenever a question asks why liquid droplets, soap bubbles, or mercury beads are spherical, the answer is always surface tension.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Surface tension is a physical property of liquids arising from cohesive forces between molecules.
A molecule inside the liquid is pulled equally in all directions by neighboring molecules, whereas a molecule on the surface experiences a net inward pull.
This net inward force acts to minimize the surface area of the liquid.

Step 2: Detailed Explanation:
Let us analyze why raindrops take a spherical shape:
1. For any given volume of liquid, a sphere is the geometric shape that has the minimum surface area.
2. Since cohesive forces pull the surface molecules of a falling raindrop inward, the liquid naturally tries to minimize its surface area.
3. This continuous inward contraction forces the liquid droplet to adopt a spherical shape.
While other forces like gravity and air resistance act on the falling raindrop:
- Gravity causes the downward motion but does not shape the droplet.
- Air resistance actually flattens the bottom of larger falling drops slightly, making them look more like a hamburger bun, but the fundamental binding force keeping them cohesive and spherical is surface tension.
Capillary action (B) describes the movement of liquid through narrow spaces and is not responsible for the shape of falling drops.
Thus, surface tension is the correct physical reason.

Step 3: Final Answer:
The correct option is (A).