the answer would be conduction
When galaxies move farther away the wavelength of the light is longer causing the galaxy to shift red but if it moves closer, the wavelength of the light gets smaller causing the galaxy to blue shift. The reason that the wavelength increases or decrease is due to the doppler effect.
Balance tubes by spacing them equally around the centrifuge and Always balance tubes with other tubes containing a same volume of liquid are right.
If you don't space them out equally, you will have a lot of broken glass to clean up...trust me. The same thing can happen if you don't have equal amounts of liquid in each tube, but it doesn't have to be exactly the same in every one.
