Question

After a long lecture, the daring physics professor stretches out for a nap on a bed of nails, How is this possible?​

Answer 1

Answer:

The reason that it is possible to lie down on a bed of nails without being hurt is that there are plenty of nails on such a bed and so there is very little actual force pressing down on any given nail.  As long as there is not much force on any given nail, it will not hurt your body to lie on the nails.  Pressure = force/area, so if you have a lot of area (many nails) you get less pressure on any given area.

There is no reason why the nails should be closer together at the bottom of the bed unless that is where you are going to sit down first (before you lie down).