It is difficult to thread a needle with one eye closed. Explain.

It is difficult to start motion than to maintain it .Explain.

It is difficult to see through a closed glass window from the inside of a well lighted room,when it is dark outside.However,it becomes relatively easy to see outside,when the lights in the room are switched off.Explain.

It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Imagine removing one electron from He^4 and He^3 . Their energy levels, as worked out on the basis of Bohr model will be very close. Explain why?

What is the necessity of eye donation? Explain