A student hangs a balloon from a string then rubs it on their hair and releases it. They rub a second balloon on their hair then move it towards the hanging balloon the moving balloon moves away because ..
A) like charges attract each other
B)unlike charges repel each other
C) like charges repel each other
D)unlike charges attract each other

The space between two 15-in.-long concentric cylinders is filled with glycerin (viscosity = 8.5 × 10-3 lb·s/ft2). the inner cylinder has a radius of 1 in. and the gap width between cylinders is 0.1 in. determine (a) the torque and (b) the power required to rotate the inner cylinder at 180 rev/min. the outer cylinder is fixed. assume the velocity distribution in the gap to be linear.