Poll of the Day > I haz a science question, but reddit hasn't responsed yet

(+) Yeah! (+)

Basically, I wanna know if gravity imparts inertia.

Lets say you are moving at a reasonably super-fast speed and you approach a large mass like a planet/star so that you have a sharp course change due to gravity and then escape the gravitational pull... lets say a solid 45 degree angle of.... inflection? (what's the opposite of deflection?)

Will you feel the effects of inertia from this change in direction?

Yes

that is called the slingshot effect

and no, you theoretically should not feel it

the only reason you feel the effects of speed is because you're going through air, which has mass

if you're just in the ship, you will feel nothing

MICHALECOLE posted...

Yes

Hard_Light posted...

no, you theoretically should not feel it

...

see, this is where I'm confused. On the one hand it's intuitive that a massive change in direction will result in interia, on the other hand as far as spacetime is concerned you're still moving in a straight line

That first guy doesnt know what hes talking about, he just said yes

Inertia is an inherent property of mass, not something that gravity imparts. That said, in the case you're describing, your inertia is why you would be able to escape the gravitational pull (or at least escape the range where it's significant, since technically gravity has infinite range but the force imparted scales down by the square of the distance) instead of being sucked directly into the planet as soon as the gravity caught you. You might not feel it, since that would be a pretty gradual force, but you still have inertia regardless of what force is acting on you.

Hard_Light posted...

the only reason you feel the effects of speed is because you're going through air, which has mass

You feel speed because of air, but you feel acceleration because of your vestibular system and the fact that everything inside your body isn't rigidly fixed and will try to stay put/continue moving on its own for a brief period after the outside of your body starts moving. That doesn't depend on air (or any other medium), since it's entirely internal.

adjl posted...

Inertia is an inherent property of mass, not something that gravity imparts. That said, in the case you're describing, your inertia is why you would be able to escape the gravitational pull (or at least escape the range where it's significant, since technically gravity has infinite range but the force imparted scales down by the square of the distance) instead of being sucked directly into the planet as soon as the gravity caught you. You might not feel it, since that would be a pretty gradual force, but you still have inertia regardless of what force is acting on you.

what i mean is, will the people in the ship get whipped up into the ceiling of their ship or not

Lokarin posted...

what i mean is, will the people in the ship get whipped up into the ceiling of their ship or not

Probably not, since the gravitational force would be applying more or less evenly to everything within the ship. If the ship were to crash into something, those within it would continue moving because that object would only have applied a force to the outside and everyone within would continue to move in the same direction until a force was applied to them (such as crashing into a wall) to change their velocity. Because gravity is pulling on all of them in addition to the ship, though, they would all move as a unit. Thinking about it, this probably actually means that they wouldn't feel it, since gravity would also be tugging on the various parts of their body that would otherwise detect the acceleration by moving independently of the rest of the body, but I could also believe that there might be enough of a difference in acceleration to detect (the vestibular system is extremely sensitive), albeit very faintly.

Hypothetically, if the velocity is high enough and the gravity is strong enough, you might see enough of a difference between how hard the inner (relative to the object) edge of the ship is pulled and how hard the crew are pulled to have them move independently, but if that's happening, that also means the inner edge of the ship is trying to move independently of the parts that are under the crew's feet, so there's a good chance the ship will just be ripped apart. I don't think you'll ever get the crew being thrown around that cartoonishly.

That said, enough media treats space travel like being in a terrestrial vehicle that if you want a slingshot manoeuvre to throw the crew against the ceiling for comedic effect, you could absolutely get away with that without letting yourself be bogged down by scientific accuracy.

Lokarin posted...

what i mean is, will the people in the ship get whipped up into the ceiling of their ship or not

that would be if the ship changed direction without the contents of the ship changing direction, like turning a vehicle.

for gravity, your path through space is actually warped. you are effectively moving in a straight line despite gravity warping that "straight line" into an orbit. for what you describe, that would have to be an incomplete application of gravity, which won't happen. gravity is affecting everything equally.

even if the substance of the planet was gone and you did a super sharp curve around the center of the gravity well, you still should not feel inertia from it.

notice in an elevator, where you do feel inertia going up and down, that is when the elevator is changing its speed differently than gravity. same with a roller-coaster. theoretically you should not feel that effect if you were to move up and down only from gravity.

though this leads me to wonder how you can detect yourself falling, but I think what you can always detect are changes in acceleration, not changes in velocity. going from not falling to falling is a change in acceleration (0 to 9.8m/s/s). if you are already falling (including being thrown up into the air, and being in a full orbit), you should theoretically not feel any change even as you pass by 0 m/s.

Ignore those nerds

The answer is yes

Sahuagin posted...

though this leads me to wonder how you can detect yourself falling, but I think what you can always detect are changes in acceleration, not changes in velocity. going from not falling to falling is a change in acceleration (0 to 9.8m/s/s). if you are already falling (including being thrown up into the air, and being in a full orbit), you should theoretically not feel any change even as you pass by 0 m/s (relative to the ground). (somehow I still imagine that you might feel it though; I'm not sure if that's from things like elevators and cartoons making me think you would, or if you really would. air resistance maybe would be noticeable, but you "shouldn't" feel any inertial effects.)

The vestibular system consists of two components: The semicircular canals and the otolithic organs. The semicircular canals (one for each axis of rotation) are filled with fluid and have a bundle of nerves that floats in that fluid and is fixed to the bottom of the canal. When the head rotates, the inertia of that fluid means it lags slightly behind and the bundle of nerves gets dragged through it, which the brain interprets as rotation (which triggers a number of different reflexes, such as the one that keeps your eyes fixed on something even while your head moves). If you spin a lot, then stop, the fluid will continue to spin, which creates the feeling of dizziness.

The otolithic organs each consist of a membrane that rests on top of hair cells, with tiny crystals resting on that membrane for added weight. When you move or are moved in any direction, those crystals' inertia mean they will exert more or less pressure on the hair cells, which the brain interprets as acceleration.

You're mostly correct in that it detects changes in acceleration (jerks), since what the brain perceives is the result of the inertia of those fluids/crystals causing their motion to lag slightly behind that of the rest of your body. The same thing also happens to any other fluids in the body, which is why you feel such motion in your stomach (there being quite a bit of room for your gastric juices to slosh around). You aren't going to feel constant acceleration unless there's a contact force providing it (such as accelerating in a car and having the seat push against you), so once you start falling, anything else you feel would be external forces like air resistance.

yes