# Air baloon and came back down about 12 hours later

1. Jan 20, 2006

### gm5170

If I went up in an air baloon and came back down about 12 hours later (assuming there was no wind), would I be half way around the globe ? this has been rattling my brain for a while. there are obviously practical difficulties, but theoretically, is this feasible ? if not, why ?

2. Jan 20, 2006

### Homer Simpson

The thing is here is that the air mass rotates with the earth as well. Otherwise the wind would be blowing at about 1000 miles per hour at the equator. If the balloon left the atmosphere I guess it would work.

3. Jan 20, 2006

### gm5170

interesting. how high up does the 'atmosphere' stretch ?

4. Jan 20, 2006

### chroot

Staff Emeritus
The atmosphere does not have a 'limit,' but its pressure decreases rapidly with increasing altitude.

From wikipedia http://en.wikipedia.org/wiki/Earth's_atmosphere#Pressure

Think about it this way. When your balloon is in contact with the Earth's surface, it's moving the same speed as the Earth's surface. The Earth's surface is, in fact, rotating at about 1000 mph (at the equator) with respect to the Sun.

Objects in motion tend to stay in motion -- this is Newton's first law of motion. Your balloon would continue moving at the same speed, 1000 mph, hovering over the same point on the Earth's surface, unless some force acted upon it. You could fire a rocket motor, for example, in the direction counter to the Earth's rotation.

You could eventually sit still with respect to the Sun, and watch the Earth's surface rush past below you at 1000 mph. As has been said, though, you'd have to deal with the air also rushing past you at 1000 mph, and it might not be a very pleasant ride.

- Warren

5. Jan 20, 2006

### Homer Simpson

Quite a bit further than a balloon will take you, like 100 km or so. It thins as you go up, so a balloon will become less bouyant a lot sooner.

6. Jan 20, 2006

### tony873004

It also depends on your latitude. If Earth had no atmosphere, and your baloon could rise anyway (baloons need air) then the Earth would rotate under you. But imagine trying this at the North Pole. You wouldn't be halfway around the world when you landed 12 hours later. You'd still be at the North Pole. The speed which the Earth rotates is ~1000 km/hr * cos(latitude). cos(0)=1 so at the equator the Earth rotates ~1000 km/hr. cos(38)=0.788, so in San Francisco, the Earth rotates 788 km/hr. cos(90)=0 so at the North Pole (& South Pole) the Earth rotates 0 km/hr.

But when you rise you will have the velocity of the ground you were on. So actually, you'd ultimately change hemispheres as you would be travelling on a Great Circle and the ground you were on holds steady to its latitude.

7. Jan 21, 2006

### gm5170

dang! so my hopes of an efficient way of travelling long distances isnt possible this way :(

thanks all 4 ur responses.