PHYS 106L Chapter Notes - Chapter 1: Lapse Rate, Partial Pressure, Compressible Flow
Document Summary
The atmosphere is a compressible fluid, made up of gases whose molecules are pulled to earth"s surface by gravity. The molecules that make up the atmosphere are most compressed close to earth"s surface, and atmospheric density decreases most rapidly with height there. The atmosphere thins out with increasing height, but never actually ends. The phenomenon is analogous to repeatedly dividing a number in half. Each division produces a smaller number, but theoretically one never reaches zero. However, since very few gas molecules within earth"s gravitational field exist beyond. 100 kilometers (km), we can consider this height an arbitrary top to the atmosphere. We may use a simple rule to describe the rate at which density decreases with height: for every 5. 6 km you ascend, there is half the atmospheric mass above you as when you started. Since barometric pressure reflects the weight of the atmosphere above a point, there is also a close relationship between height and atmospheric pressure.
