So, to my knowledge, things burn up when entering the atmosphere due to the friction caused by all of the air molecules hitting them on the way down which would make sense when an object gets faster, it hits more air molecules, and heats up, however, when an object reaches terminal velocity it no longer goes any faster, and objects that aren’t aerodynamic have a relatively low terminal velocity, meaning it may go just as fast being dropped from a tall building, and obviously, things don’t burn up (or even get hot) when being dropped from a tall building. So my question is why exactly being something falling into the atmosphere will burn up, but not if it’s dropped at a much lower height that would still reach it’s terminal velocity.
In: Physics
Okay so the thing to know about terminal velocity is that it’s kind of a simplification. The faster you move through air, the more force you need to apply to push the air out of the way. As you fall, gravity will provide a force on you, and as this force accelerates you the air you’re falling through will start to provide more and more drag. At a point, the force of your weight pulling you down, and the force of drag pushing back at you will be equal. This is called terminal velocity.
But terminal velocity is only the speed you’d fall at if you were falling for long enough through air of a constant density. When something comes into the atmosphere from space. It was travelling in a near vacuum. So there was nothing to slow it down and depending on what it was doing out in space it could be approaching the earth at a speed of several kilometres per second. Obviously this is above terminal velocity, which means it will slowly start to slow down. But if something goes that fast there’s not really any way to slow it down much.
Some other important things to note are that the earth’s atmosphere is less dense higher up so terminal velocities will be higher. And also when something is going faster than the speed of sound, drag doesn’t really work the same way. At this kind of speed air can’t get pushed out of the way fast enough to let the object coming from space through. So instead it gets turned into a superheated plasma by the object coming through it. And it’s that, not friction, which makes objects burn up and produces the majority of the heat on the way down.
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