# Atmosphere and air pressure

1. Feb 1, 2013

### salma17

At ground level, the air pressure measured with a barometer is 1000 mb. The barometer is lifted upward by a weather balloon. When the balloon reaches 2 km above the ground, the measured air pressure is 800 mb. Explain why the air pressure decreased. After the balloon goes up another 2 km (now 4 km above the ground), will the measured air pressure be exactly 600 mb, lower than 600 mb, or higher than 600 mb? Explain the reason for your answer.

For the first part, I said the air pressure decreased because there is less air above the balloon; there are less air molecules pushing down on it.
I believe the air pressure will be exactly 600 mb when the baloon goes up another 2 km. am i right?

2. Feb 1, 2013

### cepheid

Staff Emeritus

As you may know, the atmosphere gets thinner as altitude increases. Given this information, consider the first 2 km "band" of atmosphere that the balloon goes through. This "band" is actually a spherical shell, if you think about it in 3D. Anyway, how do think the amount of air in this 2 km band compares to the amount of air in the next 2 km band immediately above that? Is it the same, or less? Based on that answer, what will the reduction be in the weight of the column of air above you after travelling the second 2 km interval? The same as the reduction in weight after getting above the first band, or less?

Last edited: Feb 1, 2013
3. Feb 2, 2013

### salma17

It will be less!