So your going into the atmosphere of a planet. It is above you (you are underneath) so you are flying up into it. When you get into the atmosphere will you suddenly be falling rather than going up? It doesnt make any sense to me
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To "fly up" to a planet, you have to leave the vicinity of the earth. But once you've left the vicinity of the earth, your notions of "up" and "down" don't mean anything.
Think about it. The earth is a ball, right? What does "up" mean? It just means, "pointing away from the center of the earth". The direction identified as "up" by a person in Australia is completely different from the "up" identified by a person in the U.S. And once you're away from the earth, there just aren't any meaningful up or down directions. So you are not flying "up" into the other planet's atmosphere, you're just flying TOWARDS it.
Even your body's sensation of up and down depends on the presence of gravity. There's an organ in your inner ear that "tells" you which way is up, and it works by responding to the pull of gravity. Once you move into a weightless environment, your feeling of which way is "up" disappears.
Think about it. The earth is a ball, right? What does "up" mean? It just means, "pointing away from the center of the earth". The direction identified as "up" by a person in Australia is completely different from the "up" identified by a person in the U.S. And once you're away from the earth, there just aren't any meaningful up or down directions. So you are not flying "up" into the other planet's atmosphere, you're just flying TOWARDS it.
Even your body's sensation of up and down depends on the presence of gravity. There's an organ in your inner ear that "tells" you which way is up, and it works by responding to the pull of gravity. Once you move into a weightless environment, your feeling of which way is "up" disappears.
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Atmosphere has nothing whatsoever to do with gravity. Despite the common misconception there IS gravity in space. Astronauts in orbit only feel weightless, just like a skydiver does. They feel weightless because being in orbit means that they're just falling towards the Earth, but have enough forward speed that they in essence fall past the Earth before hitting it. That's not an analogy, it's an accurate description of being in orbit. The speed needed to attain orbit depends on altitude. At normal orbital altitudes like where the space station is this speed is about 17,000 mph. Technically it's possible to be in orbit at any altitude high enough to clear the terrain. But on Earth if you're in the atmosphere there's so much friction from the air that you can't reach and maintain these velocities. In orbit there's no air friction so if you reach orbital speed you can shut the engines off and just keep coasting at orbital speed. Re-entering the atmosphere upside down would be no different than flying an airplane upside down. Except you would burn up when re-entering unless your heat shield was on top. But astronauts re-entering the atmosphere experience several G's. This is due to their rapid deceleration though. Once the spacecraft hits the atmosphere the friction slows it down rapidly. It's this friction with the air that will cause you to burn up without a heat shield. If you were upside down the G forces would be pulling you towards the spacecraft's ceiling, up into your seatbelts rather than just down into the seat.