Question

(a) Gallinule (an aquatic bird with exceptionally long toes that are spread out over a large area) can actually walk across lily pads without sinking. Explain.
(b) One day while ewimming below the surface of the ocean, you let out a small bubble of air from your mouth. What happens to the bubble as it rises towards the surface?

Answer 1

(a) The bird exerts only a small pressure on the lily pads on which it walks because its weight is spred out over a large area by its long toes. Since the pressure is not enough to sink the lily pads, the bird can actually walk across the lily bads without sinking into water i.e., the bird can seemingly ``walks on water``
(b) As the bubble rises the pressure in the surrounding water decreases (as `P=hrhog` and with decreasing depth h,P decreases). This allows the air in the bubble to expand and occupy a larger volume (i.e., the diameter of the bubble increases).