Homework Help

Why is it that a person can lie down on a bed of nails unharmed?

user profile pic

angel-girl | Student, Undergraduate | Salutatorian

Posted July 3, 2009 at 5:11 PM via web

dislike 0 like

Why is it that a person can lie down on a bed of nails unharmed?

3 Answers | Add Yours

user profile pic

neela | High School Teacher | Valedictorian

Posted July 3, 2009 at 9:36 PM (Answer #1)

dislike 1 like

A bed of several nails are more comfortable than one single nail.Ask the person to stand one or two or just not more than 3 pins to make show!

Pressure is the weight force  divided  by the area on which the body rests. The more the area of the weight force is spread over , you feel more comfotable.

Pressure per unit area reduces if the weight force is distributed over a larger area, larger number of pins.

On the other hand you consider the reaction, you get an equal reaction from  the area on which the weight force acts by Newton's 3rd law..

The reaction or is extremely high if the man is  made to lie or stand on a single one or  two sharp nails. If the average man wieighs 70 kg , his weight force of 700 Newtons shall be reacted back from from one or two nails or needles , he will be thoroughly punctured from one side to through the body to the other side.

That is the reason a number of nails do not make pain.

 

 

user profile pic

krishna-agrawala | College Teacher | Valedictorian

Posted July 3, 2009 at 6:38 PM (Answer #2)

dislike 0 like

Whether or not a nail will pierce human body depends on sharpness of the nail as well as the pressure with which the pin presses against the body. When a parson lies on on a bed of nails having hundreds without getting hurt by nails, he takes care to ensure that the total wight of the body is resting on a very large number of pins. Thus, for example, if a person weighing 60 kilograms is resting on 1200 nails, the average weight on each nail is just about 50 grams. As there will be some difference in weight on different nails, we can assume that maximum weight on any nail will not exceed, say, 100 grams. This weight of 100 grams is not enough to exert enough pressure required to pierce the body.

user profile pic

Ashley Kannan | Middle School Teacher | (Level 3) Distinguished Educator

Posted July 3, 2009 at 8:53 PM (Answer #3)

dislike 0 like


The primary reason why a person can lay on a bed of nails and not experience physical pain (but emotional fear) is the same reason why  high heeled shoes are a hardwood floor worker’s worst nightmare.  When hardwood floors are placed down for the first time, you will be warned to not let someone with high heeled shoes walk on them for a couple of days.  They will even say that you can let an elephant walk on the floors, but not someone with high heels.  The reason is that that pressure is more focused with a high heeled shoe than the foot of an elephant, which is wider and thus spread out over more area.

When a person presses one nail against their skin, pressing it from the nail’s head, it hurts. However, when nails are placed on a board in a diffused alignment, a person can lie down on them because the pressure is not solely focused in one area.  Rather,  the division of pressure into wider area dilutes the impact.  The alignment of the nails and the level to which they are hammered into the board are critical.  If these are done appropriately

Join to answer this question

Join a community of thousands of dedicated teachers and students.

Join eNotes