When a shaving brush is taken out of water its hairs cling together. Why?

There is an agriculture field in the form of rectangle of length of 20 m and width 14 m. A 10 m deep well of diameter 7 cm is dug in a corner of the field and the earth taken out of the well is spread evenly over the remaining part of the field. Find the rise in its level.

When an air bubble rise in water, what happens to its potential energy?

Explain why When we try to close a watertap with our fingers, fast jets of water gush through the openings between our fingers

Why is it that the instantaneous rate of a reaction does not change when a part of the reacting solution is taken out?

Why does a piece of red glass when heated and taken out glow with green light?

Explain why Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently, water wets glass while mercury does not.)

Take a table - tennis ball and make three slits into it. put semicircular fins cut out of a metal sheet into these slits. Pivot the tennis ball on an axle through its centre with a straight metal wire fixed to a rigid support. Now connect a cycle dynamo to this. connect a bulb in series. Direct a jet of water or steam produced in a pressure cooker at the fins. What do you observe ?