There are three types of friction. friction occurs when an object is not moving. friction occurs when an object is moving against another surface. friction occurs in the case of wheels or other round objects. The amount of friction depends on two things. First, how the surfaces are; and second, how the object is. It is to keep an object moving than to start it moving. This is because static friction is than sliding friction. Word Bank:

static
sliding
rolling
bumpy
heavy
easier
greater