In curling, do the sweepers slow down or speed up the rock

Slicker surface speeds up the rock

Not only does it speed it up but it also prevents it from being thrown off course by any debris that may be on the ice. l think that is a lot of the reason behind sweeping as well.

Speed up and are able to direct where the rock is going as well as where it will stop

as the sweepers sweep the ice it melts and makes the granite stone speed up

The surface of the ice is not smooth, it has a pebbled surface. Brushing the ice makes it melt which allows the stone to travel farther. However, if you are wanting to make the stone curl, you wait for the stone to slightly sway in the direction you want then brush hard to keep the stone curling in that direction. This is what allows a team to play their stone behind a guard stone to protect its position on the ice. Hope this helps.