Care Bones

Why are human bones so strong?

First, they're a compound material (like fiber-glass) where the solid is a rock (calcium appetite) and the gell is collogen.
Also- look at a good x-ray of a long bone- all those arches and struts are designed (by time & experiance, yours) to give maximum strength for the least weight.
(the trick is two sets of cells - one is always desolving your bones, and the second builds up every micro break)

For weight bone is one of the strongest materials on earth, super light, flexible and strong, they are chambers of hollow walls allowing them to bend. Most people think bone is weaker than concrete because people break bones on it, but if you were to compare a piece of concrete to the exact same size as bone it would break easily. Bone is 40 times more stress resistant than concrete. Steel is 10 times stronger than bone, but is 4.5 times heavier. Bone is good with compression, a femur can hold about 1-2 tones of weight with compression strengths, but is weaker with torsion (bending) and tensile loads (stretching). Bone is made from calcium and phosphorus. 

To keep bones healthy and strong; dairy products is needed in a person's diet. How bones maintains its strength and flexibility is that every 7 years a bone replaces all of its cells, this makes bones adapt to day to day events such as running. 

Running increases the body's mass by three times, and a jump puts bones up to ten times the body's mass. Example; Currently I am an 14 year old and I weigh about 57kg. When I decide to jump; The force of jumping and landing increases my weight up to aproximately 570kg or half a ton; jumping from a roof may break my bone as this increases the force much higher which would make me weigh as much as 800 kg but since I have shock absorbers in my knees this prevent's my bones from breaking. Shock aborbers play an important role when jumping from an high height. Tendons in the knee can withstand a tonne before breaking. Cartilage absorbs pressure, it can hold about 7 tonnes before breaking! So when I jump up and down this prevents me from breaking my bones. Human's bones are well built indeed.