eli5: how does it work that for every pound of weight you lose, there is a 4 pound stress reduction in your knees?

Question

eli5: how does it work that for every pound of weight you lose, there is a 4 pound stress reduction in your knees?

In: 1542

Answer 1

Stress is by definition a body’s internal reaction to force. Force equals mass multiplied by acceleration due to gravity.

At your knees, hypothetically let’s say, you have a mass of 1 kg. The force exerted by this mass on the knee is approximately 10N. Now let’s say the mass on knee is 1 lb ie. 0.45kg, the appropriate force exerted is 4.5N. This force creates stress equal and in opposite direction.

So approximately 1 lb of mass reduction lessens stress by a multiple of 4-4.5.