I’m talking about those simple roller coasters, just after you crest a hill and start going down. Is it weightlessness, or high acceleration? I get this feeling and I’m wondering what’s causing it.
How about on viking ships? I get the same feeling at the top of the swing.
You’re falling - so what you’re feeling is an instinctive (not sure if that’s really the right term) panic.
Essentially, your ape-brain is telling you that you’re falling out of your tree, and should grab something.
So, weightlessness? Then which points of roller coasters induce high Gs? Or are they only caused by corkscrews and more complex tracks?
Weightlessness. You get maximum acceleration - at the top and bottom of the hills. At the top it opposes acceleration due to gravity, so you feel less weight (through to zero weight and then negative weight), at the bottom of the hill it is in the same direction as gravity and you feel a lot heavier. Just how much acceleration you get depends upon the engineering and evil imagination of the roller-coaster. Clearly one without captive wheels cannot go negative weight.
On a Viking ship, if the swing reaches 90 degrees, you are, for a small moment, in free fall, and thus feel no weight. Bottom of the swing you feel heavier than usual.
As has been said, you’re falling, and there is less to oppose your acceleration. It’s probably worth noting that even though you may still be going up near the top of the viking ship, you are accelerating downward in that you aren’t going up as fast.
In anatomical terms, I’d assume what you’re feeling comes mainly from stretch receptors in your abdomen responding to various soft tissues that aren’t getting pulled down as strongly as you are used to.
You experience G forces whenever you accelerate or change direction. Sometimes those G forces are negative, and sometimes they are positive. If you go down a steep drop and then up, as your direction changes you will experience positive G forces (your butt presses into the seat). A fast banked turn will induce positive G forces if your seat swings out, and negative G forces if the seat rotates inward against the swing.
Generally, the trick for designers is to get really good G forces along the spine and into the back, while minimising left/right and frontal forces (to prevent injury). The modern locking seat restraint allows higher G forces without whiplash.
Si
Oh, I don’t think I like the feeling of weightlessness then. Maybe I should rethink my dream of riding the vomit comet.
I think the feeling of falling is different than the feeling of weightlessness.
Falling is accelerating downward with nothing pushing back up on you.
Weightlessness is when you’ve reached terminal velocity and can’t even feel that you’re falling, just floating. You’d probably have to ride the vomit comet or go parachuting to experience it.
No.
Weightlessness has nothing to do with terminal velocity. In fact, once you reach terminal velocity you are effectively not weightless - your “weight” is the effective resistance that stops you accelerating. But I doubt that you could tell that. In general, falling is indistinguishable from weightlessness.
Si
Not really.
If you are in freefall there is no apparent acceleration that you can feel. If you were in a box and could not see outside you could not tell the difference between being in zero gravity or in freefall. This is one of the key points of physics.
When you reach terminal velocity you cease to accelerate - so you feel the full force of gravity. It is only whilst you are accelerating up to terminal velocity that you feel weightless, or feel as if you have less weight.
This is counter-intuitive I know.
The vomit comet dives in an as close a trajectory as it can to free fall in order to get weightlessness for the passengers. It needs power to overcome aerodynamic drag on the way down, and to keep accelerating down. It is only while it is accelerating downwards that the passengers feel weightless. When it runs out of either height or reaches its maximum safe speed it must slow down, and weightlessness vanishes.
So astronauts floating around inside the space shuttle are not feeling weightless?
They are not at terminal velocity.
Terminal velocity is something that happens in an atmosphere. It’s the point at which the acceleration due to gravity is matched by the drag from the medium you are moving through. It’s the point at which your velocity stabilises. Astronauts in the space shuttle are not moving through the air, their space craft is constantly falling toward the Earth and missing. Velocity is a speed AND a direction. Astronauts in orbit may have a stable speed but their direction is constantly changing as they circle the Earth, therefore their velocity is constantly changing and is not “terminal”.
A lot of what your body responds to is the jerk. That’s jerk in the technical sense, meaning ‘change in acceleration’, in the same way that acceleration is ‘change in velocity’.
The ‘raw sensors’ of acceleration (the vestibular system in the ears) can detect linear and rotational acceleration. Your brain processes this and assumes a constant linear acceleration in one direction to be ‘down’ and normal. Thus you aren’t alarmed when standing straight or lying on your back. Rapid changes to this (i.e. jerk) trigger a response.
Rotational acceleration inherently has a nonzero jerk as well, at least from our point of view. Any rotational acceleration will be noticed. Due to the sensors mechanism (liquid in a tube), there is some time after the changes stop that it will still be felt. This is what ‘dizziness’ is. Rapidly changing rotational acceleration (e.g. a fall followed by a tight turn followed by a twist) probably is meant to combine those effects to trigger more reactions in your brain.
wrong topic
-sorry
I know mine does.
Weightlessness is what you feel when you are not supported, but are being pulled straight down by gravity and nothiing is stopping that motion.
You will feel it if you jump out of a tree, off a diving board, or jump on a trampoline nice and high. Note that if you are going upward but slowing down, it is the same feeling as falling. You are simply accelerating downward but your initial velocity was up. The vomit comet does exactly the same thing. It heads up, then on the way up points the nose down so that it and everything/one in it is floating free as if they’d been tossed in a big arc - but without the wind resistance of being flung at 500mph.
The Viking boat thing does sometning similar; you are swung up almost vertical, until you come to a stop and fall back. For most of the upper arc you are close to weigtless because your motion is mostly vertical.
Similarly, when you go over the arc and down the really big hill in a roller coaster, you are falling nearly vertical. Of course, the front is being held back by the not-yet-over-the-hump back, which is pulled faster by the ahead-of-the-curve front. (To simplify things)
Terminal velocity (IIRC, usually about 100mph to 120mph for a human) is when you are falling so far that your velocity reaches the point where the pull of gravity is approximately equal to wind resistance. Unless you are skydiving or scored a really good acid, or that other mountain climber was lying about being your friend, you will never experience this. (Or it could be one of those wing suits in the wind shaft rides…)
Of course, if you are accelerating downward at some point you must stop - either by going “splat”, or by slowing down, or by turning direction like a roller coaster to the horizontal 9and then up again?) If you are slowing down or turning, you will experience extra forces over and above the pull of gravity.
Several things are at work; as mentioned, the feeling in your stomach that it does not need to work to hold your guts up, they aren’t pushing down any more; there’s the motion sense in your inner ear (tiny hairs being moved by a ring of fluid) that tell you if there is change in your movement; never underestimate the value of visual cues, and our instinctive fear of heights or the panic of being in a risky position.
So is weightlessness different than “hang time”?
I’ve always heard of hang time as being those microseconds where the forces pushing you up and pulling you down cancel eachother out.
Is the OP refering to hang time and not free fall weightlessness?
So, on the subject of weightlessness and astronauts, is what they feel inside a spacecraft exactly the same as what I feel on a rollercoaster? They won’t have the visual cues of the earth rushing up, the track speeding by, or even the wind in the face, but still… I don’t know how they are able to ignore that feeling and get any work done, let alone sleep, eat, and relax. I can only imagine that my mind and body would be screaming the whole time.
I only wish I could speak from experience but having talked to astronauts, their response is basically that they get used to it.
It’s actually simpler if you look at it from a relativistic perspective. One of the central tenets of General Relativity is that the reading on an accelerometer is correct. Right now, with you just sitting quietly in your chair, you are accelerating upwards at 9.8 m/s^2, as an accelerometer could tell you. You have this upward acceleration due to your seat pushing up on your butt. If you were skydiving and reached terminal velocity, you would also be accelerating up at 9.8 m/s^2, except this time the acceleration is caused by the air pushing up on you. I imagine, if you had an opportunity to get used to the feeling, that it would feel like laying in a very soft, comfortable bed (well, it’d be quite loud, too, but that’s not a feeling). Right after you jump out of the plane, before the wind resistance has a chance to become significant, that’s when you’re at zero G, as your accelerometer will tell you.