How To Walk On Nails And Feel No Pain

The answer is "all of the others are true".

Magicians, stunt men, and street performers often do a trick where they walk on a bed of nails. It seems of course, that walking on a bed of nails would be extremely painful, as the nails would poke into the skin of the foot and hurt. However, with the right configuration of the bed, walking on nails can be quite comfortable. The reason for this is that our skin will break, we will get a puncture etc. as a result of too much pressure on our skin, not too much absolute force.

Consider the following experiment. Take your hand and place the palm flat against a table. Push down hard. Nothing hurts. Do the same thing on the tip of a pen, with the same force, and it will hurt. The force in each case is the same, the difference is that the pressure, or force per unit area, is much greater in the case of the pen against your hand than the table against your hand. When there are regions of high pressure, small areas of your skin must counteract that pressure, which means that your skin must also exert a lot of force in a small area. Too much pressure, and the bounds between the skin cells are unable to exert enough counterbalancing force. The skin ruptures, you get punctured, and need a band-aid.

The bed of nails trick is all about pressure. The force pushing down on the nails is the weight of the person, while the pressure is the weight/surface area of the nails touching their foot. Anything that reduces the pressure will mean it is easier to walk on the bed. Hence reducing the weight, making the nails less sharp or more dense (which increases the surface area), or not standing on tip toes (which would decrease the surface area) all lessen the pressure. As long as the pressure is less than what skin can withstand, one won’t get punctured. Therefore with the right bed of nails, one can walk without any difficulty at all!

All of the options are correct.As:

1) You wont' bleed if all the nails are together very closely as pressure gets divided i.e. area increases.

2) You might bleed if you stand on your tiptoes .Cause area is very less.

3)You might bleed if you weigh too much.Cause the force will be very high in this case.

When numerous pins are arranged close together they form a surface. Hence it is easy to walk on them provided we do not walk on tip-toe. Thus our whole feet will be placed on the closely placed pins and pressure will be distributed throughout our feet.

$pressure = \frac{force}{area}$

Standing on your whole foot using the whole area decreases the pressure. Less weight means less force thus the pressure is decreased. The nails close together means the area is larger (I know, it doesn't really make sense); think about it as instead of multiple situations you have a big area thus the pressure is small overall as opposed to large in multiple places.

Answer: All of the others.