Question

Why is it that a person can lay still on a "bed" of nails (see the figure below) without suffering any serious injuries but would incur severe puncture wounds to his feet if he tried to stand barefoot on the same "bed"?

Why is it that a person can lay still on a bed of nails (see the figure below) without suffering any serious injuries but would incur severe puncture wounds to his feet if he tried to stand barefoot on the same bed? A person lying still on a bed of nails has his weight distributed over a much larger area than If he were standing, and so the force (pressure x unit area) on the persons skin is much greater when lying down. Because the upward force �s much greater when lying down, the net force (weight - force from nails) is closer to zero, and the nails do not puncture the skin. A person lying still on a bed? of nails takes up far more volume than a standing person, and so the buoyant force exerted by the air is much greater on a lying person than a standing person. Because the net force (weight ? buoyant force) is much less, the pressure (force/unit area) is much less for a lying person, and the nails do not puncture the skin. The weight of a person lying still on a bed of nails is much less than the weight of a standing person, and so the pressure (force/unit area) on the persons skin Is much less when lying down. Because the pressure is much less when lying down, the nails do not puncture the skin. A person lying still on a bed of nails has his weight distributed over a much larger area than if he were standing, and so the pressure (force/unit area) on the persons skin is much less when lying down. Because the pressure is much less when lying down, the nails do not puncture the skin.

Answer 1

option D is correct . it is beacuse pressure = force/ area

Answer 2

The weight of the persion is same in both cases.

In case the when the person is layins on nails in that case the total area in contact with the nails is much graeter than the case case in which he is standing.

As we know : Pressure = Force /Area = Weight/Area

So, the pressure is less when he is laying because the area of contact is much greater than that when he is standing