It does neither.

Sweeping makes the rock go straighter and decreases friction between the rock and the ice, thus making it go further down the sheet.

It increases speed relatively to not sweeping and reduces curl. That is however in a momentum perspective. Because the stone loses less speed when sweeping, the overall curl will usually be greater. The stone will decrease in speed from beginning to end no matter what you do, but the decrease will be smaller if you sweep.

Sweeping DOES NOT increase the speed. 

Pushing the rock would increase it's speed.

You're simply slowing the deceleration.

If sweeping increased the speed, the rock would never stop. 

Basically you're taking your foot of the break of a car that's coming to a stop on a flat surface, that's not increasing the speed.

Sweeping INCREASES the 

speed

 and REDUCES 

curl

.
So sometimes if you want your stone to curl a lot, it is difficult to put a lot of speed on it.

It does NOT increase the speed. It slows deceleration, learn physics... Like I said, if it increased speed the rock would NEVER stop.

If the rock travels 15mph, sweeping will NOT make it go 16mph.

The Rake is correct and LOVES being corrective, even at the cost of being unattractively pedantic. Nevertheless I do get a kick out of reading some of The Rake's stuff.

A more helpful answer to the originator of this thread would be that brushing warms the ice surface, creating a slippery liquid film which reduces friction.  This allows the stone to decelerate less quickly and therefore to go further before stopping.  At the same time it's curl between any two fixed points will not be as pronounced because, when brushed, its forward progress is quicker than its sideways deviation between those points.  In both cases, the stone might end up having curled about the same amount but when brushed it would have gone further before achieving it, thereby having curled less as it passes the point where the un-brushed stone stopped.  So sometimes we brush it to try to reduce the curl so it can get by an upcoming obstructing stone.
Another impact of brushing (on real ice) is to clean any stray debris away from the path of the stone.

I posted the correct answer before any of you, so please...

This statement by The Talent was confusing...

-----------------
 

 Because the stone loses less speed when sweeping, the overall curl will usually be greater. 

-----------------

If you think about it, if the stone is swept and runs into the far end "boards" it will have curled significantly less than an unswept stone that stops deep in the rings.  It is exactly for that reason that many stones are swept.

So the thread continued to reduce the ambiguity.  So thanks...

hello..VERY new here..but i seem to nitice if i  click my mouse instead of sweeping motion, i can stop the stone faster..or is this just my imagination?..at least it seems to work for me..

LOL just my nature, sorry. I've been playing the real game of curling since I was 15 and I'm 29 now so I know what's going on compared to a lot of people on here.

I think what Talent is saying is... in curling you might continue to sweep a rock has it curls behind because the keeps the momentum of the rock going. 

Youre sweeping is down a different line, but you're not curling the rock more. The increase in friction will make it curl more 

BUT if it loses too much speed it will stop before you get it behind a rock or such so you have to continue to sweep to bury it. The rock will be a little further down the ice but buried behind a guard or such.

It'd be easier if I could illustrate it, but yeah. 

Correct. If you put a stone without sweep on the button and then try again with same aim, but less speed, and sweep it until it reaches teeline, it will curl more than the other stone. TheRake understood me correctly...Sweeping does reduce curl in a momentum view (minimum distance view), but overall, your reduction of friction and the angle the stone has coming towards the house, means that more sweeping lets the stone get more buried, at the cost of being a longer distance from the guard. A stone given more ice and maximum sweep will have a better approach angle then a stone given less ice and no sweeping. Therefore the ideal draw would be to give so much ice that the stone exactly passes the guard with maximum sweep (given that it won't overcurl), and will be completely buried, with almost the only option for the other team to runback a guard. Sometimes it is better to have more distance to the guard, because the runback would not be very tough with short distances.

@egour: not correct. If you try, you will find that a stone deep in the rings without sweep will curl less than a stone with same ice given and swept deep into the rings.

@Talent:  I fully agree.  We must be saying the same thing without finding compatible words.

Sweeping does not speed the rock up .sweeping cleans the ice surfice and heats up the ice a little which allows the rock to keep its forward momentum and reduses curl .Since the introduction of the push broom this momentum and curling effect has been increased as compared to the old style of corn broom .The corn broon would leave debre on the ice surfice which would effect the curl and speed of the stone and make it curl more or make it die and ruin the shot 

I chose the Practice page and tried clicking the mouse to slow or stop the stone.

It seemed to make no difference.