What can you conclude about the surface of an object and the coefficient of friction? What is
the relationship?

The relationship is the normal force, that is equal to the product of the mass by gravity.

Explanation:

The friction force is defined as the product of normal force by the value of the coefficient of friction, in this way we have:

f = μ * N

Where:

f = friction force [N]

μ = friction coefficient

N = normal force [N]

On a flat surface, the normal force is equal to the weight of the body, this way we have:

N = m*g

Therefore:

f = μ * m * g

We can conclude that for a flat surface the friction force depends on the coefficient of friction, this is a value that depends on the surfaces in contact, and the weight of the body.

wavelength divides in half and speed stays the same.