Physics help! Center of mass

Question

How do you calculate the body's center of mass when one leg is raised and bent while the other is on the ground?

Answer 1

Well, you can't do it without a lot of data. A minimum would be the mass of the body, the mass of the legs, the center of mass position of the body (3 inches below navel or so), and the center of mass position of the two legs (probably a few inches above the knee. I would assume that we only have to worry about y change in COM because the COM has to stay above your foot when you balance on one leg, so the body adjusts in small ways to accommodate this. The last estimate will have to be the new COM of the bent leg which will be a slight bit higher up from the knee on the leg (further below the bent knee).

y_CMN = (M_By_CMO - M_Ly_LO + M_Ly_LN)/(M_B)

N means new. O means old. y is position. B means whole body mass. CMO means old center of mass. L is one leg (1/2 the mass of both legs). LO and LN are COMs of the leg old and new.

Hope that helps.