In a laboratory experiment, a student places a block of copper (2 kg) on a surface of a flat piece of steel and tilts the steel. The student determines that for any angle up to 30˚ (with respect to the horizontal), friction will prevent the block from sliding, but larger angles necessarily allow the block to slide. Consider the situation in which the block is not moving, and the angle of the tilt is its maximum 30˚. (Use 9.8 m/s2 for the acceleration due to gravity.)
What frictional force prevents the block from sliding?