This came up in a movie I watched recently: a golfer was tyring to make a simple putt (3 or so meters) on a perfectly flat, level green. Because reasons, the green was rotating clockwise at a certain number of RPMs (use whichever number of RPMs is easiest for you to use when you do your calculations, and assume that the hole is at the center of the green, and the radius from which the green rotates). If this happened in real life, what would happen to the ball, and how could the golfer compensate?
I believe that the ball is going to go off in one direction or the other, but I can’t grok which. The golfer, I think, would have to hit opposite to the direction the ball is going to go.
If the centre of rotation is the hole, and the golfer plays the ball towards that hole, and the green rotates clockwise, then the ball will be deflected to the left. This is an instance of Coriolis forces at work.
The ball in the video above is staying on the turntable because it can roll freely. In the scenario posed in the film we’ve got three potential options for what might happen:
The “turf” on the green is sufficient to hold the ball in place until struck, in which case Schnitte’s answer presumably applies.
The green is rotating too fast for the ball to stay in place but there’s still enough resistance from the turf to prevent it from rolling freely in all directions, in which case it would likely roll off the green (like the penny in the video).
The rotation of the green starts the ball in motion but once moving it is able to roll freely on the green like the ball on the turntable, in which case it stays on for a while but trying to putt it while also standing on the rotating green poses a whole new issue.
Based on a question I once heard:
If you are in a room and everything is like Earth but you are really on a rotating (for simulated gravity) space station, how would you know?
Answer: try to spin a coin. It will refuse to because of the conservation of angular momentum.
Specific to this thread, if the golf ball is rolling to the hole, how would conservation of AM affect it?
That’s not entirely correct. If the space station is spinning enough to provide 1-g of simulated gravity, you can spin the coin. It will drift and wobble due to the Coriolis effect, but it’ll spin. How much it drifts will depend on the size of the rotating arm. Small station = rapid rotation = noticeable Coriolis drift, very large station is slower rotation = less noticeable drift. At some given size, say a 200m station rotating at 2 rpm, the effect will essentially be negligible.
Notice that the reference frame we’re used to also rotates. Just very slowly, taking 24 hours to make a rotation. Yes, it’s true we’re not using that centripetal force due to rotation as pseudo gravity, but if you do something which is big enough and flies long enough for the rotation to become significant … then it’s significant.
OTOHm on a human scale throwing or hitting something, say of ~<150mph and ~<400 yards, Earth rotation can be ignored. It does have a real consequence, but it’s down in the noise of your measurement errors.
