If you had a hot air balloon and a realy calm windless day, could you hover in the air and get all the way around the earth by letting it turn beneath or would you just sit in one spot and move with the earth? My kid asked me this today. Any one like to offer an opinion.
Cheers Dave
personally, i think it’s plausible to do so.
although, you may need more than one day. You’d need probably a couple of years at the least, as you’d probably just move a few inches every day or week or something.
But i’m no expert on um… balloons and calm days and the rotation of the earth. It’s just my guess.
Windless indicates that the air does not move with respect to the ground. The balloon would remain over the same spot on the earth.
Interesting question. That’s a good question for The Science Guy.
Does the Earth spin in the atmosphere or does the atmosphere spin along with the Earth? I would suspect that at the height you get in a hot air balloon that the atmosphere is spinning along with the Earth. I’d say that you wouldn’t land in the same spot where you took off from, but it would take much longer than 24 hours for the Earth to spin a complete revolution beneath the balloon.
If you’re able to take the balloon all the way up to the stratosphere or all the way out to space then things would be different.
Maybe a way to test this.
Will a helium balloon on a string that is tied to the ground in the center of a closed room fall to the side of the room that is away from the earths rotation as the helium slowly escapes?
No. When you set the balloon in the middle of the room, it is stopped relative to the Earth’s surface. The only thing that would cause the balloon to move would be an external force acting on the balloon (air). But if it is a windless day, then the air around the balloon is also stopped relative to the surface of the Earth. Therefore nothing is acting on the balloon and it remains motionless.
Because I’m such a nice guy, I drew a picture that should be completely irrelavent to my explanation explained above, but I’ll post it anyway because I’m proud of the little monster that I so cunningly drew in the Atlantic ocean.
Like Harper said, wind is a relative thing, and we set it to be relative to the earth’s surface. So, with no wind and the balloon moving at the same speed as the earth and the wind, you would just hover in one spot.
The big question is whether this problem is over simplified… where you would never find such a situation where there would be no wind.
At the equator, the earth surface is moving at about 1000 miles an hour. If you could stop in mid air over that… you could hop some killer gaps 
The room is full of air. Air is a very sparse fluid… so the room is just a container of fluid. Since the room is a rigid object, the fluid will remain motionless inside the room. The balloon would have no forces applied to it that would move it to one side of the room or the other… it will only experience the forces of gravity and buoyancy, causing it to rise or fall.
As the helium escapes, the balloon will experience some action/reaction force which will cause it to move (just as if you blew up a balloon and let it go, just not quite so violent). Its movement, however, is not affected by the motion of the room.
Wind is the movement of the air, relative to the Earth. On a calm day, the air is not moving relative to the Earth. (In fact the air is moving at exactly the same speed as the surface fo the Earth.) Therefore, on a calm day, the balloon would just hover over the same spot.
In fact, I saw it happen once. I was on a motorcycle trip to Yorkshire, and a group of us sat for a while and watched a hot air balloonist who was in a state of near panic. He was becalmed exactly above the canal. He kept going up and down, hoping to find an airstream, but whatever he did, he just sat there, exactly above this 14 foot (4 - 5 metre) wide strip of water, burning his gas supply and knowing that if nothing changed, he would end up with a very wet wicker basket.
However, it would not be possible for the entire atmosphere to be calm at the same time. The land surface at the equator of the Earth moves farther than the land surface further north or south. What tends to happen is that the atmosphere lags slightly behind at the equator. This sets up big swirling eddies. This is called the Coriolis effect. The swirls are clockwise in the northern hemisphere and anticlockwise in the southern hemisphere. It’s the same effect that makes the water spin round as it goes down the plughole.
Also, the amount of lag of the atmosphere varies with altitude. A mile above the Earth’s surface, the atmosphere would have to move faster to keep up with the Earth’s surface. There is no force acting to make it move faster, so it doesn’t.
Also, winds are caused by changes in the temperature and therefore the density of the air. These changes happen because different land surfaces (or sea surfaces) either hold or reflect the sun’s heat.
If your child wants to go all the way round the world with minimal effort, he will need to become a student and take a gap year.
Here’s a thought experiment to explain one possibility.
Assumption: Calm and windless means that there is no wind due to weather and air pressure differences
Fill a large bucket with water
Get a wood dowel or similar long cylindrical object
Put the dowel in the center of the bucket
Spin the dowel like a top (spin the dowel, do not stir the water)
The water next to the dowel will move with the dowel
The water farther away from the dowel will move less with the dowel
The farther you move away from the dowel the less effect the spinning dowel has on the water
Think of the air as a low viscosity liquid. The Earth spinning is like the dowel. The air next to the surface of the Earth feels the effect of the spinning Earth. The air higher in the atmosphere feels the effect less.
The higher you go in the hot air balloon the less effect the spinning Earth has on the surrounding air. The higher you go in the balloon the more the Earth will spin below you. Next to the ground the balloon will move with the surrounding air which is moving at the same speed as the spinning Earth. Go higher and the Earth starts to spin more than the surrounding air. If you go high enough the Earth will spin beneath you more than the surrounding air will move you. The effect will be that you go up, float, and then land in a location that is some distance from where you took off. The distance will depend on how high the balloon goes and how long it stays up.
It’s a thought experiment. I don’t know if it reflects reality or not.
take a few more tabs and get back to us.
I don’t have pull tabs here at home.
check the corner by the nearest circle K
Yes, friction with the surface of the Earth (and the gravitational effect of the Earth) tend to pull the lower atmosphere round with the Earth. The higher atmosphere is further away, and the effect is lessened.
However, as I said about the coriolis effect: the equator moves faster then the tropics, which move faster than the poles. This sets up massive eddies. If you went up in a balloon on a calm day, you would eventually reach an altitude where the atmosphere was moving relative to the earth. (i.e. it was windy!) However, you would tend to be carried round in a big circle, headig up north (or down south) towards one of the poles before tracking back and almost passing over where you started rather than simply tracking round the globe at a constant latitude.
The effect is masked by a number of things, such as the effect of the sea, different land masses, warm and cold currents int he sea, and even the effect of tall mountain ranges. That is why the atmosphere is a chaotic system - all causal relationships, but impossible to predict with perfect accuracy or over a long period.
