Question

Women and overweight people often experience backpain. Let us explore the reason for this. Assume
the women has a weight of 60.0 daN before pregnancy. Suppose she gains 10.0 daN during pregnancy,
due to weight of the fetus, placenta, amniotic fluid, etc. To make the calculation easy, but still realistic,
we shall model the unpregnant women as a uniform cylinder of diameter 0.30 m. We can model the
added weight due to the fetus as a 10.0 daN sphere with a 25.0 cm diameter and centered about 5.00
cm outside the woman’s original front surface.
(a) By how much does her pregnancy change the horizontal location of the woman’s center of gravity?
(b) How does the change in part (a) affect the way the pregnant woman must stand and walk? i.e.,
what must she do to her posture to make up for her shifted center of gravity?
(c) Can you now explain why she might have backaches?

Answer 1

a. Cgchange=10daN*(.05m+.125m)/70
=1/7 (.175m)=.025 or 2.5 cm outboard from the original axis.

b. He has to lean back to keep from falling frontwards.

c. getting the cg lined up, moves the upper body backwards, like a guy walking around bending backwards looking up all the time. Your lower back muscles are constantly in tension to pull backwards, as your expanding uterus is getting weaker. It is actually more complicated that this, hormones, joints, are also involved. A pregnant mom isn't going to see a physicist for back pain... http://www.babycenter.com/0_low-back-pain-during-pregnancy_9402.bc