A would be the wavelength, C would be a crest, D would be the amplitude, leaving B which is the trough.
Answer:
what do you mean by this?
Explanation:
Answer: a.) Roughness of the surfaces in contact with each other .
Higher the roughness of surfaces in contact with each other, greater is the friction between bodies. Force of friction will be less between smooth surfaces.
b.) Weight of the sliding/rolling body: greater the weight of the moving body on the surface, more is the force of friction on the body by the surface.
I hope this helps