Do electromagnetic waves need a medium to travel through, like mechanical waves do? Explain why or why not

Calculate the mass of an object that has a momentum of 100kg x m/sec and velocity of 4 m/sec

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.

What type of force holds atoms together in a crystal?