Now that the stage has been set, it’s time to examine the forces exerted on any object coming through the atmosphere. Two things can happen if the angle of entry is not just right for space shuttle reentry: if the angle is too shallow, bounce off the atmosphere like a rock on water and if the angle is too steep, the shuttle will heat up too fast and far too much for the heat shields to withstand and probably incinerate the shuttle. Almost all meteors are incinerated before ever reaching the ground, but there is also the possibility that the meteor will ricochet off the atmosphere like the space shuttle could.
When the object begins its decent into Earth’s atmosphere, its speed is incredibly high. The object begins to compress the air in front of it. If we assume the air is an ideal gas, we apply the ideal gas law (PV=nRT where P is pressure, V is volume, n is the number of moles of a given gas, R is the ideal gas constant, and T is temperature in Kelvin) and see that if the pressure is going up, temperature also has to increase. Furthermore, this ram pressure, “a pressure which is exerted on a body which is moving through a fluid medium, causes a strong drag force to be exerted on the body.” (http://en.wikipedia.org/wiki/Ram_pressure) The drag force slows the object down, but the friction associated with drag adds to the inferno growing around the object. This same pressure is possible to be exerted on objects leaving the atmosphere or flying in the atmosphere, however, the speeds required to obtain the similar effects are almost impossible to reach near the surface do to air resistance and aren’t felt as a shuttle is put into orbit since pressure is constantly decreasing rather than increasing and by the time the shuttle is up to its orbit speed, the pressure has almost gone to zero.
With the temperature increasing, material expands. Space shuttles are designed to withstand these thermal expansions. Meteors are rigid and when they expand, they end up breaking up which catalyzes their incineration in the atmosphere.
http://newsimg.bbc.co.uk/media/images/41380000/jpg/_41380943_shuttle_land_203.jpg (left)
http://www.stratcom.mil/fact_sheets/images/reentry_brief2.gif (right)