What would happen if I drilled a, say, one foot diameter hole through the Moon, from pole to pole. (Assuming the Moon has poles, so to speak.)
Now, I drop a golf ball down the hole, dead-centre.
Presumably the ball will accelerate to the centre (based upon the Moon’s mass) and then decelerate until it reaches the other side; and then lather, rinse, repeat.
There’s no air friction. Will the golf ball continue to oscillate in this pattern forever?
Even interstellar space isn’t a perfect vacuum, so there is some small about of friction, so, no.
Correct.
There are two effects that are independent of any air friction: the first is gravitational radiation, which will (very very slowly) drain the energy from the system, and second, the golf ball’s interaction with the microwave background radiation of the universe, which (if I’m not mistaken) - the ball will be slowed in either direction because the radiation impinging on the “forward” side will be blueshifted (and thus of higher energy) than the radiation impinging on the other side. This also will be very very slow - I think the sun would expand to absorb the Earth and Moon before either effect was measurable.
Come to think of it, tides from the Earth and other planets will perturb the golf ball, causing it to hit the sides of the the hole long before anything else happened.
A bigger perturbation on the golf ball would be that the Moon is not of uniform density, so the gravitational forces on the ball would be somewhat non-uniform, meaning your little pendulum trick would not work perfectly. How imperfect it would be, precisely, I don’t know and I don’t know a quick way of finding out. We’d need details on precisely how the Moon is laid out and where the big concentrations of mass are, stuff I’m guessing NASA learned throughout the 1960s as part of the Apollo project.
Yeah, that too.
Ok. So let’s assume a uniform mass for the moon.
Interstellar space may not be a perfect vacuum, but what if (in this experiment) it was?
Does my Titleist oscillate indefinitely?
We can postulate a truly perfect vacuum and a uniform Moon, but I can’t see any way to postulate away the gravitational radiation. Though in the real world, there will pretty much always be other effects that aren’t quite perfect and which will be of greater significance than the gravitational radiation.
Assuming you also eliminate tidal effects on the ball (from the Earth, Sun, etc.), the gravitational radiation and interaction with cosmic radiation will eventually slow the ball to a standstill over truly vast time lengths
No.
The gravitational effect of the Sun has an effect to the ball’s motion too. If not the Sun, then the next closest star.
The only thing I can think of that may stop your infinite oscillation maybe perturbations in the rotation of the moon. I do not know if the moon’s rotation wobbles like the Earth does but if it does then your golf ball will eventually start hitting the sides of that hole.
There’s also friction with the sides of your tunnel to consider too.
Wait a tick. Since the moon is revolving around it’s axis that means the gold ball has a sideways (translation?) velocity when you let go. Doesn’t it do like anything thing else that’s dropping into a lower orbit? IE shouldn’t that sideways speed pick up and it would hit the side even if the moon was perfectly uniform in density and a perfect sphere?
So, why isn’t the Moon being pulled closer and closer to the Earth?
The moon is not only not of uniform density, it is non-uniform in a quite regular way. The densest part of the moon, its core, is on the near side, and the crust is thicker on the far side. It’s a frozen tidal bulge; the Earth’s gravity drew the heavier elements nearer itself before the crust froze. A hole drilled nearside-to-farside would work for the proposed plan, while a hole drilled from side to side (relative to the Earth) would not. That ignores local variations, of course.
Mainly because its spinning around the earth
There’s one other factor I think would exist even in an ideal system. Gravity is a two way attraction. While the moon is pulling the golf ball around much more noticeably, the golf ball is also pulling the moon towards itself. As the golf ball moves it’s minutely dragging the moon along with it. I believe the net effect of this over a few billion years would be to synchronize their movement with the golf ball motionless in the center of the moon.
Only via gravitational radiation. Newtonian gravity does not contain any mechanism which would cause this to happen.
IIRC, the moon is slowly pulling away from the earth. Is this a gravitational effect, or due to orbital velocity? If the latter, will it eventually reach equilibrium?
In either case, I think this would result in an eventual collision between the ball and the wall.
Ok, I’ve been think about this a bit more and as far as I can tell it’s totally not going to work. If I drilled a hole from the near side to the far side in the middle of the disc at the equator I have a bit of a problem. The moon rotates once every 29.5 days and the circumference is about 6800 miles. That means at the top of the hole the hole and the ball are both moving sideways at about 10 miles per hour. However as you go down the hole the hole is moving sideways at a speed slower than that so the ball hits the side on the way down. Basically in order to stay in the tunnel at all points the ball’s sideway(translational) speed needs to match the hole and I think the geometry just won’t let that work. (Hell the hole on the other side is moving in the opposite direction. If the ball was in an orbit then gravity could reverse the direction but we don’t have the option here.)
Of course if we have a non rotating moon it might be possible.