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Physics Misconceptions

January 4th, 2014 · 2 Comments

How do airplanes fly?
I was taught in high school that the reason a wing provides lift is because the top is curved more than the bottom and that the air flowing faster over the top has less pressure. There is some truth to that, but the major source of lift is angle of attack, the front of the wing being higher than the rear. As a child I experimented with this effect by sticking my hand out the window of a moving car and noticing how the air would strongly push my hand up or down depending on how I positioned it. The curved top of a wing helps to smooth out the airflow and reduce turbulence and drag, but has a smaller effect on lift. If you doubt this, then consider how a plane can fly upside down. It’s not quite as efficient because the airfoil is working against you, but angle of attack easily counteracts that.

Why does a meteor burn up?
We frequently hear that a meteor or re-entering spacecraft heats up because of “friction” with the air. It’s true that the object moving through the air will generate some heat from the air rubbing against its sides, but most of the heat is generated by the air being compressed in the front (i.e. “Ram Pressure“). As the meteor enters the atmosphere, air in front is unable to move out of the way as quickly as the meteor is falling, and the air gets extremely compressed. Compressing a gas raises its temperature. Think about where the heat shield is on the old Mercury or Apollo capsules: On the bottom surface that leads its descent. The sides of the capsule are much less insulated because the air flowing over the sides adds little heat.

Tags: Computers, Tech & Science

2 responses so far ↓

  • 1 Mom // Jan 4, 2014 at 5:01 pm

    Now we know why you and Pierre (and most all other dogs) like to ride with their heads out of the windows. Air conditioning has spoiled that.

  • 2 Don // Jan 5, 2014 at 8:33 pm

    Did Mom just call you a dog?

    One issue they ran into as they were attempting to break the sound barrier is the thickness of a plane’s wings. You’ll notice planes that are designed to do so typically have a much thinner wing for the size of the plane than say a 737 or even a Cessna 150.

    Anther thing they changed on supersonic planes was the rear elevator. Most of them have the whole rear wing pivoting rather than just a trailing edge. That actually has to do with angle of attack too.

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