But beyond being a good movie, it reminded me of something I just read in renowned MIT physics professor Walter Lewin’s For the Love of Physics about why astronauts are weightless in orbit. If you think it’s because they’re far enough away to no longer be affected much by the Earth’s gravity—which is what my intuition was, without having thought about it seriously— think again.
Now, if they had travelled up a space elevator, for instance, and were standing on the top floor, 559 km up, they would feel only 15% lighter. The reason they feel 100% lighter instead… is that they are in free fall. The Hubble Space Telescope, the International Space Station, and space shuttles and satellites when they’re in orbit, are all in the process of falling back down to Earth. As Professor Lewin explains, “The reason why the astronauts don’t go splat is because the Earth is curved and the astronauts, the spaceship, and everything inside it are moving so fast that as they fall toward Earth, the surface of the planet curves away from them.” And of course, if the force of gravity were really negligible up there, they wouldn’t keep circling the Earth; they would shoot off into space in a straight line.
Even though I have two years of high school physics under my belt, and have tutored high school physics now and again over the years, I still had it wrong. It’s a humbling reminder, for me, of how imperfect human intuition can be.