I was listening to a podcast about the geocentric model of the solar system vs heliocentrism. Apparently a “proof” at the time that the earth was not spinning was that if you tossed a ball into the air, it would land right back where it started (assuming a perfectly vertical toss). If the earth was spinning, the logic goes, it would land a good bit away. The answer of course was that the earth and the air that surrounds it is moving.
That’s all easy enough to understand in this day and age but it got me thinking…
Why does the surrounding gas (air) move so in sync with the solid (earth)? It doesn’t seem like there is anything to really to drag the air along with the planet except a tiny amount of friction.
If you toss a ball up in a plane, for example, it follows the path of the plane because the air is trapped between walls. But the air over the earth has no such containment, the surface of the earth has no boundary. It seems like there should be some slippage.
Actually that’s wrong - the ball is already moving with the earth when it is in your hand. Tossing it straight up doesn’t change that, there’s no reason why it should suddenly move backwards when it leaves your hand. Air has nothing to do with it, that would happen in a vacuum too.
To the original question, it is gravity and friction together doing this. But not completely; weather generally moves from the west to east because the earth is revolving east to west under the atmosphere, which is only partially dragged along with it.
Not sure why that would be the answer. If I set a basketball on the back of a flatbed truck and accelerate, the ball will not follow along even though it is being acted on by gravity.
There is slippage. The Coriolis force is apparent via this slippage, and from there the weather systems. So the slippage is manifested as the cyclonic form of high and low pressure systems, and from there the direction of winds.
Actually the earth revolves the other way, west to east (counterclockwise as seen from above the North Pole). The prevailing winds are in opposite directions in most of the northern vs southern hemisphere. The direction of prevailing winds is a complex mix of prevailing pressure differentials at different latitudes plus Coriolis forces as already mentioned, and look like this:
Indeed, and even then the friction induced by gravity may be enough to allow very, very, very gradual acceleration without the ball rolling backwards. And of course once you reach a steady velocity it’ll sit there quite happily.
I actually tried the ball-tossing experiment as a young-un. I was disappointed to find that the ball dropped neatly back into my hand.
A slightly older, slightly wiser me decided that the earth’s movement would have been too subtle to demonstrate any effect of 10-year-old Mean Kid Mustard tossing a rubber ball five feet in the air.
Yes. The Earth’s surface is accelerating, constantly in a circle, but you need more patience and something more sensitive than your hand and a ball. Like this:
Actually, the critical word in L_J’s thesis is “accelerate.” The basketball, stationary truck, and Earth are all moving at the same speed and direction. When the truck changes in relation to the Earth by driving away, the basketball gets left behind – less the effects of friction.
Umm, isn’t the Earth moving at a constant velocity, not accelerating?
Just want thank the OP, this thread is giving me major flashbacks to all the time I’ve heard this all explained to YouTube flat Earthers!
Of course the friction is tiny, but so what? That just means that it would take a long time for the air to (mostly) come to rest with respect to the surface… Maybe as long as a day or so?
But it’s had four billion years. Even with only a very tiny amount of friction, that’s plenty.
Gravity affects air, too, but there are other things going on with weather, such as the surface of the Earth heating because of the sun, exciting air particles, plus changes in humidity, etc.
Felix was still subject to gravity at 128K feet, though. You have to escape gravity to let the Earth spin below you without pulling you along.
But the fact you are moving in a circle is acceleration, from a physicist’s point of view. The acceleration is what makes the Foucault pendulums alluded to above change their direction over time.
