Will the giants leg hold.. ?

Question

"Will the giants leg hold? How does the pressure (counted in N/cm2) on a cross section of a humans leg change if the length is multiplied by 10? How big could the giant get if the legs could stand a pressure of 1000 N/cm2 and a normal human beings leg has a cross section of 8 cm2? (1 kg has the weight 10 N)"

Help me please?! You'd be saving my life!!

Answer 1

As you get bigger, your volume (and thus weight) increases as the cube of size, but the cross-section of your legs (and presumed strength) only increases as the square of size.  So being 10 times as big without changing shape puts 10 times the pressure on your leg.

For the second part, a "normal human" cross section (and they must be talking about the bone only, because that's way too small to be a whole leg) of 8 cm^2 could hold 8000N.  If you figure a normal human weighs about 150 pounds = 68.4 kg = 684N, then the bone has a "safety factor" of about 11.7 - it could hold 11.7 times your actual weight.  So in theory, a giant could be 11.7 times as big before its bones snapped under its own weight.  Of course, this only applies if it stands still its entire life.  In practice, it would have problems much sooner.  You need that 11.7 safety factor if you're physically active. Real life "giants" almost all develop back and/or leg problems at less than twice normal size.