A flute has several holes in it. Why?

Hole is

A hollow sphere is filled with water through a small hole in it. It is hung by long thread and as water slowly flows out from the hole at the bottom, one finds that the periods of oscillation first increases and then decreases. Explain. Why.

SO_3 has zero dipole moment. Why ?

Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her?why?

What are holes in semiconductor?

Watching the sunset on a beach, one can see for several minutes after it has 'actually set'. Explain.