Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: myuncle on 13/04/2021 09:38:29
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As a result of the previous thread I tried to google about speed of arrows-bullets inside a free falling vacuum chamber. And I haven't found any, can you help me?? How can this be even possible? I know they did experiments in a static vacuum chamber on the ground, but I haven't found anything about projectiles inside a free falling vacuum chamber. It could be done easily on the ISS. Example, they could assemble a long vacuum chamber/tube/channel. Inside the vacuum tube, at the end of each side (A and B), they put an automatic crossbows or gun. Then calculate if the projectile fired from A to B (travel direction of the ISS) would be slower than the projectile fired from B to A (opposite the travel direction).
Or, they could easily do the same experiment by dropping a long vacuum chamber from the sky.
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If the entire assembly is in free fall there is no way anything inside the chamber can know which way the chamber is moving, therefore AB ≡ BA.
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If the entire assembly is in free fall there is no way anything inside the chamber can know which way the chamber is moving, therefore AB ≡ BA.
Why? Point A is yellow, point B is green. How long does it take for the arrow to travel from A to B, and how long does it take for the arrow to travel from B to A.
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I don't think the speed of a projectile is affected by the color of the target.
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Why? Point A is yellow, point B is green. How long does it take for the arrow to travel from A to B, and how long does it take for the arrow to travel from B to A.
Travel time from A to B equals the travel time from B to A
If you are in an airplane with no windows there is no experiment you can do to prove whether you are flying at 600 mph or sitting on the ground. In the free fall example, if you are on a space station there is no experiment that you could do to prove whether you were in free fall of just sitting out in deep, deep space and not under the influence of any gravity source.
You got admit Alvancalvard's color comment was pretty funny.
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Why? Point A is yellow, point B is green. How long does it take for the arrow to travel from A to B, and how long does it take for the arrow to travel from B to A.
Travel time from A to B equals the travel time from B to A
If you are in an airplane with no windows there is no experiment you can do to prove whether you are flying at 600 mph or sitting on the ground. In the free fall example, if you are on a space station there is no experiment that you could do to prove whether you were in free fall of just sitting out in deep, deep space and not under the influence of any gravity source.
You got admit Alvancalvard's color comment was pretty funny.
Then you can't do any measurement. How can you measure the speed of a car, athlete, cheetah, train? We simply use a clock, and measure how long does it take for the car, plane, boat, to travel from point A to point B, no need to take into account the movement of the Earth, Solar system and galaxy. Arrow or bullet inside the train is no different, it's done in the same way, you don't need to take into account the speed of the train.
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Precisely. Provided the vector AB is not accelerating, AB ≡ BA. If you've ever had the experience of peeing in an accelerating train or a turning airplane, you will recall what happens when the system accelerates.
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Why? Point A is yellow, point B is green. How long does it take for the arrow to travel from A to B, and how long does it take for the arrow to travel from B to A.
Travel time from A to B equals the travel time from B to A
If you are in an airplane with no windows there is no experiment you can do to prove whether you are flying at 600 mph or sitting on the ground. In the free fall example, if you are on a space station there is no experiment that you could do to prove whether you were in free fall of just sitting out in deep, deep space and not under the influence of any gravity source.
You got admit Alvancalvard's color comment was pretty funny.
Then you can't do any measurement. How can you measure the speed of a car, athlete, cheetah, train? We simply use a clock, and measure how long does it take for the car, plane, boat, to travel from point A to point B, no need to take into account the movement of the Earth, Solar system and galaxy. Arrow or bullet inside the train is no different, it's done in the same way, you don't need to take into account the speed of the train.
You make your measurement by choosing the reference frame that makes the most sense to measure in respect to.
If you are measuring a car, cheetah, etc, it makes most sense to measure the speed with respect to the ground.
With the ISS, it makes the most sense to measure the speed relative to the center of the Earth and not relative to the ground.
For a crossbow bolt fired in a vacuum chamber in the ISS, it makes sense to measure it relative to the ISS.
If you fire two bolts one in the direction of the station's orbital velocity, and one in the opposite direction, then relative to the station, they both will travel at the same speed. Relative to the Earth, one bolt will travel at the ISS speed + bolt speed, and the other at ISS speed - bolt speed. ( at these speeds you can get away with straight velocity addition and not have to account for relativistic velocity addition.)
However, it should be noted that in the ISS scenario, the station is in orbit. Thus the bolt fired forward will start to climb into a higher altitude due to its increased speed relative to the Earth, and as it does so, will give up speed for altitude gained, and the bolt fired in the other direction loses orbital speed, and drops to a lower altitude while picking up speed relative to the Earth.
The result will be that the forward fired bolt will decrease the rate at which it pulls ahead of the Station and the rear fired bolt will also decrease the rate at which it falls behind the station ( the increase in speed it gets is in the orbital direction of the ISS)
This is of course assuming that the bolt speed relative to the crossbow is less than the orbital speed of the ISS.
The point is that orbital mechanical considerations complicate the ISS scenario with additional factors.
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If the entire assembly is in free fall there is no way anything inside the chamber can know which way the chamber is moving, therefore AB ≡ BA.
https://en.m.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment
I know its light so it's as good as posing witchcraft as proof, but it's the closest to the ops inquisity I think.
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Janus, very nice. Frames of reference.