the nerds are wrong, it's because the earth likes humans and lets them fall without burning
Terminal velocity is around 200 km/h, which is not fast enough for heating to occur, but because of how both Earth and meteors are moving and one has to catch up with the other, the minimum velocity a meteor can enter Earth’s atmosphere with is Earth’s escape velocity, which is around 40000 km/h.
I’ll do my best to explain.
Escape velocity is the velocity needed to escape our gravity well. If you launch something straight up from Earth at less than escape velocity Earth’s gravity will immediately start accelerating it down, towards the center of Earth. At less than escape velocity this acceleration towards Earth will eventually overcome all of the initial velocity you gave the object and the object will fall back, eventually hitting with the same velocity you launched it with.
In your example of a meteor moseying into our gravity well at say 10 km/h Earth’s gravity will immediately start accelerating that meteor towards the center of the Earth. It will hit at escape velocity plus 10 km/h.
If we imagine that the meteor could pass straight through Earth, our gravity would start slowing the meteor down instead of speeding it up once it had passed through the center of the earth, but because it does so at escape velocity plus 10 km/h our gravity is not enough to bring it to a stop, just to slow it down enough for it to exit our gravity well once again going 10 km/h.
Not anything near Earth's orbit. Anything entering from outside and headed straight for Earth. Since escape velocity is the exact velocity Earth's gravity can cancel out for something headed straight away from Earth before it leaves our gravity well, it is also the velocity it can add to something headed straight for Earth. That makes sense since it is the exact same force. Most things that enter our gravity well do not pass straight through the center of it of course. Earth's gravity will still accelerate these things towards the center of the earth, but this will just curve their trajectories a bit for the most part.
Decaying orbits do not have a lot to do with escape velocity. That's as far as I understand it mostly the moon's gravity fucking things up. A Lagrange point is as you say a point in orbit where for example Earth and the moon cancel out eachother's gravity so your orbit will not decay. This is however still well within Earth's gravity well (which is huge). An orbit is just being in a gravity well and traveling at less than escape velocity.
No problem! If I see an opportunity to use my Kerbal Space Program addiction for something productive, I'm taking it. I just hope I'm not coming off as too insane.
That was just meant as a quick joke about how if I'm on the same sanity level as everyone else here I am clearly insane. Thank you for your concern comrade, but I'm actually having the time of my life rambling about orbital mechanics with everyone and this was not really meant to convey insecurity or fear. It might have been in bad taste, considering that people actually do share real problems and concerns here. In that case I'm sorry, otherwise don't worry!
It's helpful to visualize Earth's gravity well as a literal well--a corridor that things fall down to impact Earth. If you start outside of it, you have to traverse the whole tube in order to hit the planet. "Falling" that far imparts a certain amount of energy, regardless of what you were doing before you "jumped in" to the well. If you fell straight through the well and then "up" the other side, you'd come out at the other end with the same velocity you had before you entered, since the energy is conserved. Since you started outside the well, you have to have enough velocity to exit the well again. That's escape velocity. Therefore, anything captured by Earth's gravity well has to (more or less) be moving at at least escape velocity when it gets to the planet itself.
Remember that gravity is (among other things) a way of accelerating. In Earth's case, something "in our well" is having its velocity increased by 9.8 meters/second every second. Until you hit atmosphere, there's basically nothing else counteracting that acceleration, so you can pick up quite a bit of velocity with respect to the ground. There's no such thing as a terminal velocity in space, so you can get going good and fast. Once you hit atmosphere, all that kinetic energy has to go somewhere as other forces start decelerating you toward your terminal velocity. Heat is among the places that kinetic energy goes.
Your explanation is way better than my rambling answer I think. But just to nitpick a bit, 9.8 meters/second every second is the surface level acceleration, but since gravity weakens with distance and the edge of the gravity well is the furthest point from earth you could conceivably "drop" something and have it ever landing on earth, the initial acceleration would be incredibly slow. If we imagine a meteor that starts off static relative to earth and at the very limit of our gravity well it might be accelerated by a cm/year every year for the first few thousand years, and might take a million of years to actually hit. But when it hit it would do so at pretty much perfect escape velocity, and if it could pass through Earth it would just barely not escape our gravity well and would eventually fall back after another 2 million years.
Yeah, there's a lot of weird details here that can complicate things; I was going for a very basic answer. Even in the kind of case you're talking about, it's unlikely that the object would stay in a stable equilibrium--if it's really that close, perturbations from other objects' gravity would almost certainly kick it out of that cycle. The solar system is chaotic, and orbital dynamics get messy. Thanks for the elaboration, though!
Of course! Moon fuckery alone messes up orbits enough that you quickly realize this is impossible even without bringing the gravity of the fucking sun or Jupiter into it. It was just meant as an example of how gravity works and what escape velocity is. So this is what orbital mechanics says would happen if there were only two bodies of matter in the entire universe.
Could you please explain the second part of your answer regarding the minimum velocity? Is there no way that a meteor could be moseying around our solar system, drifting slowly until it gets pulled into Earth’s gravity?
It might be possible for something kinda small to have been in the same orbit around the sun as the Earth but moving at a speed that would be canceled out by the Earth's gravity pull by the time the object entered the atmosphere.
I think I see what you are saying, but it is not possible for anything to have the same orbit around the sun as Earth but move at a different speed. The speed is the orbit.
not an
astrophysistastrophycistastrophysicist , so what do I knowBut wouldn't the ability to maintain an orbit be a function mass as well as speed? Even if it was a decaying orbit?
Or did I just answer my own question? A smaller object (or would it be more correct to say, object with smaller gravitational effect?) would have to be moving faster than a larger slower moving object to share an orbit around the sun..
Damn, if I just learned something I'm gonna need my money back from hexbear dot net. :troll:
But wouldn’t the ability to maintain an orbit be a function mass as well as speed?
Nope. It doesn't matter if it's a feather or a brick. If you apply an equal force to objects of different mass, the less massive object will accelerate more - however - the amount of force exerted by gravity depends on the mass of the objects. A larger object will produce more gravitational force, but it requires more force to accelerate. A smaller object will produce less gravitational force, but requires less force to accelerate.
The mass of the object gets canceled out in the equation, leaving you only with the mass of the other object (i.e. the planet being orbited/fallen towards) and the distance between them.
Also not an astral physician, but I think actually no. Using the moon as an example, I'm pretty sure we technically orbit the moon, while the moon orbits us. It pulls us back and forth as it orbits around us, and that balances out since it comes from all directions. If you trace the Earth's orbit around the sun close enough we should be moving in a slightly wobbly or spiraly shape. I think since gravity pulls equally on all matter, a satellite and a planet with the same speed and direction would have the same orbit, and to mess with that you would have to increase our mass to the point where we were affecting the sun's orbit. But please don't make Earth massive enough to seriously affect the sun's orbit, because no one would ever be able to break the high jump record again.
Astronauts do not have to move at escape velocity. They are nowhere near the edge of our gravity well. If they have been in orbit, they do have to enter the atmosphere at around orbital speed however. That’s around 9 km/s, which is why anything returning from orbit is covered in heat shielding and material meant to burn up instead of the craft, because these craft experience a lot of shock heating.
You can skydive from the edge of space, because that’s actually not very high, so you don’t reach too terrifying a velocity. You could not skydive from orbit (mostly because you’re in orbit, you wouldn’t actually fall down). If you entered the atmosphere at orbital speed you would burn up. And experience winds strong enough to pull teeth. Hard to say what exactly would kill you, but it would do so very quickly.
The fucken nerds over at /r/askscience keep deleting my question because it “is based on fundamentally flawed premises”. Fucken dweebs can’t appreciate a good couple of questions.
It's next to impossible to have discussion let alone questions on reddit. It's a platform for smug reactionary tech bros to be "right" about everything on.
Your question was based on fundamentally flawed premises, and they didn't wanna bother to explain why the premises were flawed.
I can understand that, watching forums where questions based on zero knowledge of the subject of the forum are asked every day is frustrating. But even a rudely worded "The speeds involved are completely different, look up reentry heating. And terminal velocity isn't a set number." Would have been a million times better than what they did.
But that sounds "unprofessional" or whatever bullshit, and they want to sound official and proper at all times. Only insecure losers that care about that kinda stuff become reddit mods.
Complete layman answer, but yeah I'm pretty sure it's because meteors are already moving incredibly fast and so the friction destroys them before it could slow them down to terminal velocity.
FWIW, it's a common misconception that the heat from re-entry is due to friction. While it does contribute in a small way, the vast majority of the heating experienced by meteors or spacecraft is due to compression. They're moving so quickly that air literally cannot get out of their way fast enough, and so they end up "squishing" the air in front of them. Reducing the volume of a parcel of air heats it up (same principle that helps drive pistons in internal combustion engines), so as more and more compressed air piles up in front of the object, it gets hotter and hotter. This heat is harder to dissipate, because it's the air itself that's warming, not just the object.
Yep. This phenomenon is also what determines the sound barrier. At subsonic speeds, air is simply being displaced, but as you transition past mach one, the air cannot be displaced fast enough so it begins to be compressed instead.
because the human body is about as dense as water (1K/l) while rock is about 10 times that on average, so while air resistance won't let a human get past 300km/s, it will burn a meteor coming at 10km/s Idk about warmth tho is seems counter intuitive to think they would be hot as they fall through cold air
My physics is a bit rusty, but air resistence only depends on velocity and surface area, not density no?
Furthermore, meteors tend to enter the atmosphere at high velocities, so there's a lot of friction, and since they're much more massive the air resistence won't slow them down that much, because they have a ton of momentum
This thread feels like an elaborate bit.
Also, meteors are bigger and they travel at terminal velocity (same as light), so they can absorb more photons than human skin (which is reflective because of oils), and that makes it appear to be in fire when in reality it's just breaking the light barrier.
Why do meteors burn up going through our atmosphere whereas skydivers don’t?
Because meteors are traveling at much, much greater speed relatively. Like imagine even something just orbiting the earth: it's likely traveling at kilometers a second since it has to be going fast enough to keep missing the atmosphere as it falls, and if it loses enough speed to enter the atmosphere it's going fast enough that the friction creates plasma and heats it up a lot. Meteors are things on completely different trajectories from the earth itself intersecting it, meaning both they and the earth are moving very fast in at least somewhat different directions.
To put it another way, they get hot because they are being slowed down very rapidly by friction (or more accurately, they experience a lot of friction because they are moving fast, which slows them down very fast), while a sky-diver isn't slowing down and is instead simply prevented from accelerating more than a certain amount by that friction.
not all skydivers
https://www.youtube.com/watch?v=NOkolBZE3qk
Because there's no oxygen in spa e meteors tend to be made up of material which would spontaneously combust the moment it interacts with the air
