Friction on Inclines

“A box slides down a ramp with no friction. How would the box's acceleration change if friction were now present between the box and the ramp? Explain your answer. Imagine a block sliding down a ramp. If friction is introduced between the block and the ramp, what effect would this have on the net force acting on the block? Explain your reasoning. A sled is moving down a snowy hill. If the snow becomes less slippery, increasing the friction between the sled and the hill, how would this affect the sled's speed as it moves down the hill? Explain your answer.”