Here's a breakdown of the factors involved:
* Pressure = Force / Area Pressure is the force exerted on a surface divided by the area over which that force is distributed.
* Large Number of Nails = Large Surface Area When there are many nails, the weight of the fakir is distributed over a large surface area. Each individual nail then bears only a small fraction of the total weight.
* Reduced Pressure on Each Nail Because the weight (force) is distributed over a large area, the pressure exerted by each individual nail on the body is significantly reduced. If the pressure is low enough, it won't break the skin or cause serious injury.
* Blunt Nails While some nails may be sharper than others, typical beds of nails don't use needle-sharp points. Blunter points further increase the contact area and reduce pressure.
* Even Weight Distribution The fakir needs to distribute their weight evenly across the bed of nails. This prevents any one area from bearing too much pressure. A slightly curved or contoured bed of nails can also help with even weight distribution.
* Slow and Controlled Movements Sudden movements or shifting weight can increase the pressure on specific nails and cause injury. Fakirs typically lie down and get up slowly and deliberately to maintain even weight distribution.
* Pain Tolerance and Training While the physics is the primary explanation, some element of pain tolerance may be involved. Over time, practitioners may develop a higher threshold for discomfort.
In summary: The bed of nails works because the large number of nails increases the surface area over which the body's weight is distributed. This significantly reduces the pressure exerted by each individual nail to a level that is not enough to cause serious injury, provided the weight is evenly distributed and movements are controlled.