Question

Jim is performing a magic show where he has to lie on the plank fixed with 1000 nails. He weighs 650N. Each nail has an area of 0.000001 m2. The pressure requires to penetrate through a person skin is about 700kPa.
a) Calculate if the meddles will pierce through him when he lies in the nails. b) Calculate if the needles will protect through him if there are only 800 needles in the plank

Answer 1

a) They will not pierce his skin

First you need to find the average force on each needle, which can be found by dividing the total force (650) by the number of nails (1000). This gets you can average force of 650/1000, or .65 N. To find pascals, you divide the force in newtons by the area in square meters, so you get .65/.000001, which is 650000. You can divide that by 1000 to convert it from pascals to kPa, which gets you 650 kPa, which is less than the 700kPa needed to pierce the skin.

b) They would pierce the skin in this case.

Here, the average force would be 650/800, which is .8125. With the same .000001 m^2 surface area, you'd get .8125/.000001 pascals, which is 812500 pascals. Divide this by 1000 to convert to kPa and you get 812.5, which is higher than 700, so it can pierce the skin.