Which describes the molecular motion of a solid nickel marble rolled across the floor?
a. the constant vibration of the nickel atoms that make up the marble
b. the motion of the nickel atoms due to contact with the floor
c. the transfer of atoms from the top to the bottom of the marble in response to gravity
( i am pretty sure it is a)

Amichelson interferometer operating at a 600 nm wavelength has a 3.02-cm-long glass cell in one arm. to begin, the air is pumped out of the cell and mirror m2 is adjusted to produce a bright spot at the center of the interference pattern. then a valve is opened and air is slowly admitted into the cell. the index of refraction of air at 1.00 atm pressure is 1.00028.how many bright-dark-bright fringe shifts are observed as the cell fills with air?