# Spin theoryMarch 29, 2015 11:38 PM   Subscribe

Twirl an upside-down soda glass and toss it down a tabletop (somewhat like the hero in the video game Tapper), and the glass will pull off in a direction opposite of the spin. Spin a granite curling stone and throw it down the ice, however, and it will travel in the same direction as the spin. Video blog SmarterEveryDay looks at physics theories that try to figure out why this counterintuitive result happens.
posted by a lungful of dragon (7 comments total) 17 users marked this as a favorite

I haven't watched the video but I've always understood this to be that the force of the mass of the glass being accelerated over the surface is less than the friction of the glass on the surface, whereas the rock's force from the mass accelerated is more than the friction of the surface. So, they head in opposite directions when spun the same way. This is why you can affect the trajectory of a rock by altering the surface's coefficient of friction by sweeping. But then, I'm Canadian.
posted by jimmythefish at 1:32 AM on March 30, 2015 [2 favorites]

seems like they ought to try a glass on the ice, and a curling stone on the table, too
posted by thelonius at 2:25 AM on March 30, 2015 [4 favorites]

Have they tried yelling "HURRYHAAAAAAAAAAAAAAAAAAAARD!" at the soda glass?
posted by Kabanos at 8:18 AM on March 30, 2015 [7 favorites]

22 minute video on all, and I do mean all, of the details of preparing a curling sheet.
posted by benito.strauss at 10:40 AM on March 30, 2015

I haven't watched the video

It sounds a bit more involved. I recommend watching the video, if you're interested.
posted by a lungful of dragon at 11:36 AM on March 30, 2015

Having curled a few times (why yes, I'm Canadian, why do you ask) and the proud possessor of a physics degree, I loved this video. It seems counter-intuitive that more friction = more melted ice -> less friction, but hey, that's why you test those things.

Like the video maker, I would guess that both sets of researchers are right, and the degree of effect is what's really up for grabs.
posted by sauril at 11:48 AM on March 30, 2015

I've always accepted Shegelski's theory about the water movement. I had no idea there were competing theories.
posted by jacquilynne at 6:09 PM on March 30, 2015

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