Explain why pregnant women often suffer from back strain late in their pregnancy.
Because of the shift in the body's Centre of mass, a stress is created, which is why pregnant women frequently experience back pain later in their pregnancy.
Pregnancy is the period during which a woman's uterus gives birth to one or more children.
In the late stages of pregnancy, the baby is quite heavy. This causes torque to appear on the spinal cord. This leads to back pains in the pregnant woman.
Due to the shift of the centre of mass of the body a torque is generated as shown in the figure below.
Stress developed due to this torque is responsible for back pains during pregnancy.
In other words, a Growing uterus is responsible for the aching of the back. The expanding uterus causes the center of gravity to shift, stretching and weakening the abdominal muscles. This changes the posture and puts a strain on the back. Plus, the extra weight carried by the body means more work for the muscles and increased stress on the joints.
As a result, pregnant women frequently experience back discomfort later in their pregnancy.
When you push a piece of chalk across a chalkboard, it sometimes screeches because it rapidly alternates between slipping and sticking to the board. Describe this process in more detail, in particular explaining how it is related to the fact that kinetic friction is less than static friction. (The same slip-grab process occurs when tires screech on pavement.)
When a glass bottle full of vinegar warms up, both the vinegar and the glass expand, but vinegar expands significantly more with temperature than glass. The bottle will break if it was filled to its tightly capped lid. Explain why, and also explain how a pocket of air above the vinegar would prevent the break. (This is the function of the air above liquids in glass containers.)
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