If hot air rises, why is it colder as you get farther up from the Earth's surface?

Answer 1

Heat is motion--literally. Molecules moving faster means more heat. The more you confine that motion to a smaller area, the higher the temperature--which is why the bottom of the bike pump gets hot.

The opposite is also true. The more space you have for a given amount of heat (movement) the lower the temperature. The temperature is cooler the higher you go because you literally have more space for the air molecules to spread out up there, which equals a lower temperature.

Light and heat are not the same, but an example with light that's easy to see may help you understand. The light of the Sun falling on your skin can burn you over time, but focus a small amount of sunlight with a magnifying glass and it can burn you instantly. Same with heat--compress it into a small area, and the temperature goes up. Let it spread out, the temperature goes down.

Answer 2

That always confused me too.

The reason it gets colder is as follows:

First of all, air does not absorb light as well as solid matter does. So sunlight travels from the sun, through the Earth's atmosphere (where relatively little is absorbed) and then it hits the surface. Here some is reflected back, and the rest is absorbed, thus increasing the temperature of the surface.

As is the case with any hot object, heat will escape and warm the things around the object. The closest thing to the surface of the earth is the air at ground level. So that air gets hot, and some of that heat travels to the air higher up, and so on.

Here's a much more thorough explanation:

http://www.chemistryquestion.com/English/Questions/ChemistryInDailyLife/47c_temperature_elevation.html

Answer 3

Read about earth's atmosphere on wikipedia.

http://en.wikipedia.org/wiki/Earth%27s_atmosphere

In particular, read about the different layers of the atmosphere individually.

This is a summary of what I read on Wikipedia:
The lowest layer, the troposphere, is the layer your question and experience cover. The surface of the earth is heated by the sun more effectively than surrounding air, so it warms the air near the surface. As air temperature increases, density decreases, and a convection cell develops. Air pressure decreases with elevation because the pressure is due to the weight of all the air above you. When the air rises, the atmospheric pressure decreases, so it has to expand. Whenever a gas expands against an external pressure it cools (Joule Thompson effect).

As you get in to the next layer, the stratosphere, temperature increases with altitude! In this layer, most of the energy absorbtion from the sun occurs at the top of this layer (related to ozone uv absorption). Since the top is hotter than the bottom, the hotter air is already floating on the cooler air and there are no convection cells. Also the lack of convection cell turbulence makes it safer to fly airplanes in this layer.

Answer 4

Simply because the solid ground is what keeps air the warmest, while empty air like high up from the surface can't contain its heat as well.

Answer 5

This may be easier to understand.
The air is thicker closer to the ground.
This is because of gravity.
As you go higher there is less air which means less heat.
If you are familiar with compressed air it gets hot during the compression phase. As the compressed air is released it feels cool.
The explanation can get more complicated but this is easy to envision.

Answer 6

The ideal gas law can be used to explain it.

P*V=n*R*T

(pressure*volume)=# of moles of gas*universal gas constant*Temperature (deg Kelvin)

Basically this is how it works...
Take an air parcel near sea level and move it to the top of a mountain...holding V, n, & R constant during the process. You'll notice that as P decreases--T will also decrease due to the relation.

Answer 7

Reflected solar energy from the sun is what heats our lower atmosphere. Thus the farther you get from the earth's surface, the cooler it will be.

Answer 8

the air cools.
a sunny day atop a mountain is warmer than a dark winterday in a valley which frost up quicker in winter also.