What Does Sweeping Do, Really?
Let's imagine the sport of curling without sweeping for a second. The shooter lets go of the rock, and then everyone just stands there silently, watching it go down the ice. No yelling of the "hurry hard" variety, nothing. Pretty uninteresting, right?
So, that begs the question: does sweeping really do anything, or is it just something we made up in order to make the sport look more exciting?
The effect of sweeping the ice in front of a moving curling stone isn't all that obvious to the casual observer, so perhaps a little skepticism is understandable. But, really, sweeping does make a difference. Really! You can trust us. It's subtle, but it's very important, and can make the difference between winning and losing.
As veteran curlers know, you sweep a rock for two reasons: to make the rock travel farther, or to keep the rock traveling straighter (i.e. curl less from side-to-side). The exact science behind sweeping has been studied and debated over the years, and there are actually several articles in peer-reviewed science journals about it. But the basic idea is that sweeping warms up the ice directly in front of the rock, reducing the friction just enough to allow you to extend the rock's path for an extra six feet or so, depending on how good you are at sweeping. (Note that sweeping does not melt the ice surface as was once thought, but it does warm the ice, which alone is enough to slightly reduce the friction.)
"Six feet? That's it? Big deal." Well...six feet is the difference between a rock sitting just outside the house, and a rock sitting right on the button in the center of the house. In curling terms, that's a pretty big difference! If you're talking about the last shot of the game, that six feet - or more, if you're really good at sweeping - can be the difference between winning or losing the game. The shooter still needs to do his or her part and give the shot a chance - not every shot can be "rescued" by sweeping, certainly - but it's up to the sweepers to do the fine tuning. It adds an entirely new dimension to the game, and among other things, it requires a level of physical fitness that would otherwise be far less important in curling.
"But how do you tell in advance whether a rock needs to be swept?" Experience. Many top curlers use stopwatches to give them a little bit of numerical guidance regarding how fast a rock is moving upon release, but even without a stopwatch, this is something that sweepers generally get a better "feel" for as they gain experience.
"What about keeping the rock straight? How much of a difference does sweeping make there?" It's hard to put a number on this aspect of sweeping since a rock's curl depends more on how fast the rock is moving - whether it's a hit or a draw, for instance - than the sweeping. But let's look at it this way. Even if sweeping only affects the curl of the rock by one inch - one measly inch - that can make a huge difference. For instance, it can mean the difference between a shot crashing on a guard, or getting around the guard and into the house. And that's just one example.
"Now, about all that yelling. That HAS to be for show, right?" Well...okay, some curlers tend to go a little overboard in their sweep calls and their "HURRY HARD"s and whatnot. We'll concede that point. But communication between the Skip and his or her sweepers, whether it's in the form of extreme yelling or at a more controlled volume, is vital. The sweepers have the best perspective on how fast the rock is moving, but the Skip has the best view of the line the rock is taking. So, should you sweep a rock or not? Maybe, maybe not - it's up to the Skip and the sweepers to communicate with each other all the way down the ice.
"Does sweeping work the same way on both dedicated curling ice and arena ice?" The basics are the same, but sweeping has more of an effect on dedicated curling ice than it does on arena ice. That's because dedicated curling ice has more texture, or "pebble", then arena ice does, and textured/pebbled ice makes sweeping more effective.
"I've seen some old curling highlights where people aren't using synthetic 'brooms' like today. Instead, they're using actual straw brooms to sweep, as if they just grabbed one out of their kitchen. There's no way sweeping with a broom like that makes a difference, right?" This just goes to show you how sweeping has evolved over the years. Back in "the day", curling took place outside, and curling ice had all kinds of imperfections. Back then, you just swept a rock to get frost and debris out of the way. Over time, ice conditions improved, and broom technology improved along with it, such that we sweep rocks for an entirely different reason today.