7 ms·
How are you able to achieve 0G while still within the escape velocity of earth, what's the science behind this?
by 40acres 8y ago
How are you able to achieve 0G while still within the escape velocity of earth, what's the science behind this?
- deleted 8y ago[deleted]
- koolba 8y agoSame way you’d experience it in an elevator if someone cuts the safety cable. With a plane they can repeatedly climb / drop to recreate the experience.
- MystX 8y agoThe jet flies parabolic arcs in the sky. If you imagine you shoot a bullet on a 45 degree angle upwards, it follows a ballistic path in a big arc right? Now fly that same path with a big plane. The bullet and the plane are both in freefall essentially.
- deleted 8y ago[deleted]
- jonsen 8y agoFree fall. Like inside an elevator with a broken cable. Here the aeroplane starts the free fall with considerable upwards speed. That and the horisontal speed form an upward parabola path of free fall.
- djsumdog 8y agoThat's how Hollywood studios do a lot of their anti-gravity shots as well. They have to be shot really quickly, in short takes, with custom planes that have movie sets built into the interior. It's pretty crazy and dangerous when you think about it.
- deleted 8y ago[deleted]
- gambler 8y agoFascinating. Didn't know they use real zero-g. Do you have links to any articles that describe the process in more detail?
- chrisco255 8y agoHere's a video of Kevin Bacon and Bill Paxton in the vomit comet from Apollo 13: https://www.youtube.com/watch?v=5IAAjk3QdU8 https://www.youtube.com/watch?v=5IAAjk3QdU8
- vxNsr 8y agoThere are a whole lot of random sharp edges there to be jumping around and then suddenly dropping out of the air every 30 seconds. one of them almost faceplants into something, yikes!
- JumpCrisscross 8y ago> what's the science behind this? Earth's gravity in low-earth orbit is almost the same as on the surface [1]. What makes things on the ISS float isn't their distance from earth. It's horizontal (or more accurately, tangential) speed. Objects in orbit are in free fall. To replicate that, parabolic flights free fall. (Parabolic paths are similar to the elliptical paths orbiting objects take [2].) They then stop free falling (to avoid hitting the ground) before climbing back up and doing it again and again. And again. [1] https://en.wikipedia.org/wiki/Low_Earth_orbit#Orbital_characteristics https://en.wikipedia.org/wiki/Low_Earth_orbit#Orbital_charac... [2] https://history.nasa.gov/conghand/traject.htm https://history.nasa.gov/conghand/traject.htm
- qznc 8y agoThis always reminds of the Hitchhikers Guide: "There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss." ISS constantly falls down to earth. It is also moving so fast that it constantly misses earth.
- 40acres 8y ago>> ISS constantly falls down to earth. It is also moving so fast that it constantly misses earth. I'm gonna have to roll up some herb while you explain this comment further.
- Dylan16807 8y agoIt is always accelerating straight toward the center of the planet at ~1G.
- superice 8y agoThink of firing a canon sideways: it takes a while for the cannon ball to drop and hit the earth. Now imagine firing it faster and faster, till eventually it's dropping at the same rate as the earth curves. That is essentially what the ISS is doing at a height of about 400km above the surface.
- PhasmaFelis 8y agoAny time you're not resting on a surface, hanging from something, or otherwise being held up against gravity, you're in freefall. ("Zero G" is admittedly a bad term, since there's no such thing as "zero G" literally anywhere in the universe. It's all freefall.)
- Gitnumb 8y agoHave done Zero G, it's fun if you have money to burn. The floating is fun but I got sick towards the end.
- CydeWeys 8y agoYou can't truly experience freefall except in a vacuum or in an object that is producing an accelerating force to counteract the force of air resistance (like a really fast elevator, or a vomit comet plane). The reason is that the air itself is imparting substantial acceleration upon you from you hitting it, which leads to terminal velocity. Once you reach terminal velocity the air pressure is imparting exactly the same kind of force against you to repel gravity as the floor would be at ground level, so you experience one full g. You only really feel weightless the moment you jump off a surface, before you've accumulated any velocity and thus before you're being accelerated by air resistance.
- mirimir 8y ago> Once you reach terminal velocity the air pressure is imparting exactly the same kind of force against you to repel gravity as the floor would be at ground level, so you experience one full g. And what's interesting, is that what feels "down" is actually "up". Which is one of the gotchas in flying. > You only really feel weightless the moment you jump off a surface, before you've accumulated any velocity and thus before you're being accelerated by air resistance. This is a very useful thing in ice skating, skiing, martial arts, etc. Especially combined with changing moment of inertia.
- crimsonalucard 8y agoNet G relative to your frame of motion is zero G is a better way to put it. G is a unit. 9.81 Newtons. So 3G is 3*9.81 newtons.
- derekp7 8y agoAnother way of picturing this, is what happens when you throw a baseball. You typically aim at about a 45 degree angle, let it lose from you hand, then from that point on the ball experiences free fall until it lands on something (well, not exactly, due to air resistance, but close enough).
- jonsen 8y agoAn airplane can get closer. It can actively compensate for air resistance.
- chrisweekly 8y agoAstronaut training is done the same way in a modified Boeing 727(? IIRC), nicknamed the "vomit comet". As a student pilot I used to love doing heavy-G steep climbs then pushing the nose over and enjoying a few seconds of weightlessness....
- LoSboccacc 8y ago> what's the science behind this? The same: in both cases the vessel is falling toward earth accelerating at 1g, so for the passenger that are also experiencing 1g of gravity it feels like they're floating
- TangoTrotFox 8y agoPretty common misconception, but what you're implying is not how/why you have 0G in space. So for instance the space station still experiences about 90% of Earth's gravity. Orbit is about going really fast, horizontally. If you flew straight up to the ISS, you'd fall right back down. This is why when you see a rocket take off their course looks extremely bent - it's not an optical illusion. So why horizontally? Imagine there was no air resistance on Earth. If you shot a bullet that bullet would keep going until the force of gravity pulled it down and it hit the Earth. But now imagine that you shoot it fast enough that the vertical distance gravity is pulling it down is less than the vertical distance it gains due to the curvature of the Earth. That equilibrium is exactly what orbit is. It also leads to the highly counter intuitive fact that the height of a given circular orbit is determined exclusively by how fast an object is moving relative to the body it's orbiting. Mass doesn't matter. Okay so back to the plane. If it's not intuitive yet imagine throwing a ball. It works exactly the same as our bullet, but we can visualize one important part easier. The ball's trajectory will be a parabola. And at the highest point of that parabola the net vertical force on the ball is zero. It's where the force you exerted on it to send it up, and the force of gravity pulling it down eventually reach an equilibrium. Something inside of that ball would experience 0g at the moment when it was at its parabolic peak. And that's exactly what these planes do. They simply 'throw' the planes into a parabolic path, and the passengers experience near 0 g while traveling through the parabolic peak.
- jonsen 8y ago...throwing a ball... disregarding air resistance it will be in free fall all the way back to the ground. There is nothing special about the peak.
- crimsonalucard 8y agoOrbiting a planet is basically free fall with translational velocity. If the earth were flat we would fall down and horizontally and eventually hit the ground. However the earth is a sphere and the direction of the free-fall constantly adjusts itself to point towards the center of the sphere creating an orbit. It is literally throwing oneself at the ground and missing.
- hathawsh 8y agoThey fly the plane downward, matching the vertical acceleration with the acceleration caused by gravity. You owe it to yourself to see these amazing videos filmed on planes that simulate zero G: OK Go - https://www.youtube.com/watch?v=LWGJA9i18Co https://www.youtube.com/watch?v=LWGJA9i18Co Physics Girl - https://www.youtube.com/watch?v=q1_AJWZajEk https://www.youtube.com/watch?v=q1_AJWZajEk Veritasium - https://www.youtube.com/watch?v=SAQ-iIJkLzA https://www.youtube.com/watch?v=SAQ-iIJkLzA
- JumpCrisscross 8y ago> They fly the plane downward, matching the vertical acceleration with the acceleration caused by gravity "Contrary to popular misconception, the 0 g freefall phase of flight begins as the aircraft climbs, and does not occur solely as the aircraft descends. Although the aircraft has upward velocity during the initial 0 g phase, its acceleration is downward: the upward velocity is decreasing" [1]. [1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2598414/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2598414/
- hathawsh 8y agoGood clarification, thanks. By "downward", I meant downward acceleration, not necessarily downward velocity, although colloquial usage of "downward" usually means velocity.
- modernerd 8y agoAnd Stephen Hawking! https://youtu.be/jhCPincElC4?t=49 https://youtu.be/jhCPincElC4?t=49
- jerf 8y agoYou've already collected a nice set of replies, but here's another way of looking at it: Imagine the Earth is a single point mass at its center of mass. Now consider the collection of orbits around it. You still have (to a first approximation) all current orbital possibilities as you know and love them. But now you also have a lot of new orbits. There's orbits just a few inches above the point mass that require nearly the speed of light. There's orbits at what is now ground level. And there are all kinds of elliptical orbits that go through what is now the ground. All of those orbits represents trajectories in which you are in free fall. The primary reason these orbits don't "exist" is that they impact the surface of the Earth [1]. However, if you "ride" one of these orbits briefly, you still get the free fall effect, just as if you were in orbit! It's just that you can't stay on the orbit freely because of the minor issue of surface impact. When you juggle or something, the balls are actually, very briefly, in orbit. Minus air resistance, which is a big deal for a ball. (I initially wrote "throw a baseball", but air resistance becomes a factor very quickly even then.) With a powered projectile, like, say, an airplane, you can deliberately overcome the air resistance for a while and stay in the orbit for longer, even through the atmosphere. It may seem like a bizarre idea of "powering" through an orbit, but it's perfectly reasonable. It's still a gravitational orbit, it's just that electromagnetic forces (contact forces) are getting involved and mucking up the purity of the orbit, so we cancel them out briefly with other ones via the jet engines. If you had a device that could continue powering through the Earth, you could stay at free-fall even through the rock. [1]: The secondary reason is that the Earth isn't the aforementioned point mass. A neutrino could hypothetically "orbit" through the Earth for a while before being captured, but its orbit will be complicated by the fact that as it goes below the surface, the "mass" of the Earth starts dropping. Which makes me wonder if there ever are any such neutrinos. The only thing stopping such a thing from existing is the need for a process to create neutrinos that have less than escape velocity for the Earth, and I'm not sure if there is such a process.
- IshKebab 8y agoTry jumping.
- stetrain 8y agoThere's a difference between experienced "G-Force" and the amount you are accelerating due to gravity. Basically, gravity can accelerate you all that it wants, but if there is no force resisting that acceleration (air drag, your feet against the ground, the seat pushing on your back in an airplane) then you don't feel that acceleration. https://en.wikipedia.org/wiki/G-force https://en.wikipedia.org/wiki/G-force "Gravitation acting alone does not produce a g-force, even though g-forces are expressed in multiples of the acceleration of a standard gravity. Thus, the standard gravitational acceleration at the Earth's surface produces g-force only indirectly, as a result of resistance to it by mechanical forces. These mechanical forces actually produce the g-force acceleration on a mass. For example, the 1 g force on an object sitting on the Earth's surface is caused by mechanical force exerted in the upward direction by the ground, keeping the object from going into free fall."
- robotresearcher 8y agoAny time you fall freely you experience this. If you jump off a table you are weightless[1]. Unfortunately a planet is accelerating at you so the experience doesn’t last long. You can choose your frame of reference when considering interacting masses. I choose mine, which gives the interpretation above. [1] ignoring buoyancy and drag from air, which are small in this scenario.
- bbojan 8y agoBecause 0G is a (slightly imprecise) term for weightlessness, and weightlessness is by definition when the only force acting on a body is the gravitational force. If you're in an elevator, and the elevator cable snaps, you'll be in free fall (at least initially), although you are nowhere near the escape velocity.