How does applying oil to a bicycle the bicycle to work better?

The frequency of the fundamental of the guitar string is 320 hz. at what speed v do waves move along that string?

The two most prominent wavelengths in the light emitted by a hydrogen discharge lamp are 656(red) and 486 (blue). light from a hydrogen lamp illuminates a diffraction grating with 500 lines per mm, and the light is observed on a screen 1.50 behind the grating. what is the distance between the first-order red and blue fringes?

What is "decrease in velocity" i need offering 60 !