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In our previous article we talked about distances and measurements. Using simple physics principles and some math we found, that the distances in curling could be easily measured with a common stopwatch. Let us remind you the formula:

It describes distance from the hog-line to the stop-point of the stone. As you remember, w - is a deceleration coefficient, constant for uniform ice. What's about V – it is velocity of the stone on the hog-line. We accepted it as:

and after combining (1) and (2) it appears as:

Well, the only thing that influences distance S is time that stone spends during moving from the backline to the hog-line. But there is weak point in the last equation. This point is that (2) is an average speed. In fact, we are interested in instantaneous speed on the hog-line Vhog, but (2) congruent with the one only in case of uniform motion.

Let’s try to explain. Stone will move like (3) only in case of nothing affects its movement except the friction force. So it is possible only after release of the stone. And the very moment when your hand is very-very close to it, but you already do not touch the way of its own movement. That is why the release process is so important in Curling.

Take a look on the figures below:

Scary, aren’t they? On the left chart we can see how stone will move from backline to hog-line. Vertical axis – is a curling sheet between two lines, horizontal axis – is time. And between two timestamps stone passed between two lines. Easier now? On the right graph – stone velocity. It is absolutely constant between two timestamps and nothing changed during release moment – green circle. And moreover, it is the same as average stone speed (well, it should be obvious). So we can say that these figures represent uniform stone motion. And in this case (3) will work perfect!

But who is able to push the stone uniformly all 27 foots? Nobody! Quite the contrary every curler tries to correct stone movement between back- and hog-lines, or he can lose his balance and hold a stone or push it - in other words change its velocity. You can say: “But Curling champions can!” No again! Even if you would be the Best Curler Ever Seen in the Universe you would not be able to move uniform because of… friction. Your (and stone velocity since you hold it) decreases, as it decreases after release until stone’s stop.

Now, let’s come back from stars to the Earth. If we are common Curlers, as we are, our process of real stone movement between back- and hog-lines will look like this:

First graph is not a curved trajectory of the stone – it shows us that Curler moved not steady, he was moving faster or slower. …seems, he lost his balance. And the second graph really shows us that stone velocity was not constant. And in the middle Curler started to speed-up the stone (graph goes up). Definitely, he was doing something wrong…

And what is really bad in this case, that common velocity measured with a common stopwatch – will be average velocity. And it will be different than exact final velocity of the stone on the hog-line (green circle). As you can see, velocity deviation may be considerable and as a result, evaluation of desirable stop point will be with sufficient error. Remember, when you measure weight and stone goes further than you expected… That’s awful! The very same will be in our example.

There are two ways to measure correct stone weight. First is to move uniformly between two lines. But that may be possible only for the Best Curler Ever Seen in the Universe, but do you know him?..

The second way that can guarantee correct data for (1) is precise measurement of Vhog instead of average velocity. You may ask “HOW?!” Well, soon we'll share with you some ideas.