# Paradox while Cooling & Heating in Air? [duplicate]

I was thinking about how asteroids get "burned" up in the upper atmosphere as they approach the earth surface due to the atmosphere of earth heating the asteroids immensely as a result of air compression which is nothing strange.

This however seems opposite of things I observe day to day. While I am travelling in my car I open my window, and to my surprise the car became very chilly and I develop goosebumps (body response to cold), so I am inclined to think that the temperature of my body dropped slightly as a result of me travelling in our Air.

This creates a sort of paradox, for a person travelling at asteroid-speeds s\he would say that as we speed up we heat the objects up, but for a person who travels at day-to-day speeds they would say as we increase in speed we cool things down, but both cannot be correct so who is correct?

So my question is at what speed does temperature raise and not fall as we travel through air? And if so why is that?

## marked as duplicate by John Rennie, Brandon Enright, Jim, Danu, David Z♦Sep 7 '14 at 8:07

• possible duplicate of After what speed air friction starts to heat up an object? – John Rennie Sep 6 '14 at 19:37
• A person dropping into water at around 100mph will say that water is very hard - almost solid and hitting it will break all your bones and kill you. A person dropping into water at 1mph will say that water is very soft and hitting it will save you from a long fall. – slebetman Sep 7 '14 at 0:14

A breeze at 35°C and 90% humidity (typical conditions in Houston, Texas) doesn't cool you off. It just makes you feel even more miserable. A breeze at 40°C and 20% humidity (typical conditions in Phoenix, Arizona) doesn't cool you off, either. It, too, just makes you feel even more miserable.

Your body cooled because the air velocity was much lower than the speed of sound and because the air was cool, and perhaps dry as well.

None of the above have anything to do with why an object entering the Earth's atmosphere heats up, sometimes drastically. Those reentering bodies are initially traveling at many times the speed of sound. The high speed means air can't flow around them smoothly. It instead develops a shock. The air in front of the shock is heated by a very rapid compression. Some of this extremely hot air (so hot the gas turns into a plasma) will flow inside the shock front, e.g., where the reentering body is. The flow can be extremely turbulent, and oftentimes, non-ideal. The combination of heat and vibration is what tears an incoming meteorite apart.

There are several major difference between the asteroid and you.

You have moisture on the skin. As the air passes over the skin, it picks up the moisture, making you feel cooler.

The asteroids are travelling hundreds of times faster. The compression of air increases the heat substantially. You would barely notice the heat increase from a car.

• A passenger airplane travels many times faster than an automobile, and yet they don't suffer much compression heating. The problem becomes acute only for an object traveling a good deal faster than the speed of sound. – David Hammen Sep 6 '14 at 19:58