MAC cannon projectile speed?

tsassi wrote:

TheDeathSummer wrote:

Relative to the location of the original firing point is fine.

This doesn't answer my question. "The original firing point" is uniquely defined only at the time of firing. After that it's ambiguous and depends on your choice of coordinates.

See, there's this concept of a coordinate system where you define an origin, a base point, and then at any point in time you tell where an object is by how far and in what direction it is from the origin. You can have different coordinate systems, these coordinate systems move relative to each other, and "speed" is only defined with respect to a given coordinate system.

Consider this: there is a train moving past a station. In the train there is a bottle on a table. There is a man sitting in the train. The origin of his coordinate system is where he sits. In his coordinate system, the bottle is stationary, it is not moving relative to him, the direction and distance of the bottle to him is always the same, it has zero speed. There is another man on the station. He also has his own coordinate system, where his position is the origin. Because the train is moving relative to him, and the bottle is in the train, it is moving relative to him, the distance between him and the bottle is growing, its speed is greater than zero. These two men observe a different speed for the bottle, because they are measuring the speed in different coordinate systems.

Crucially, one has to understand that there is no absolute universal coordinate system. No coordinate system is better, or more correct than another. The speeds measured by the two men are both correct. There is no such thing as the "true" speed of the bottle.

Normally, on Earth when we say something is moving, we really mean that it is moving relative to the ground. So if I say "the train was going 50 m/s", everybody understands that it was going 50 m/s relative to the ground, because that's a convention we've implicitly agreed upon. Our coordinate systems in which we measure the speeds of things on the ground are all stationary relative to each other. However, this convention hardly makes sense when we are hundreds of light years away from Earth in the middle of space, because we can't even see the ground on Earth. So, the question "moving relative to what?" becomes relevant. And the "what" has to be a concrete object. You can't say, "oh, relative to this point" because that "point" depends on your chosen coordinate system, so it's circular reasoning.

And so we get back to my question: moving at 30 km/s relative to what object in the scene?

tsassi wrote:

TheDeathSummer wrote:

Again, moving at 30km/s relative to the original firing point is the objective and accurate answer. I'm not going to say "relative to the Dark Energy located at the original firing point." because a narrator doesn't actually need to maintain a physical frame of reference for even a nanosecond to calculate the speed of an object. How can the location of the original firing point be more unreliable and ambiguous than the 500 meter ship that's moving backwards? I mean, they're basically exactly the same thing. The only difference is that the latter alters the calculations massively and gives very damning implications for other space battles in Halo. You yourself have said "the motion of the Frigate is irrelevant" after all.

Okay, let's take a step back for a moment, forget the frigate, and make a thought experiment. Suppose you are alone in the universe, floating in empty space with a gun that has a single bullet in it. Let's say that the muzzle velocity of the weapon is 1000 kilometers per hour. You fire the weapon.

1. Where is the "original firing point" an hour after firing? How far from it are you, roughly?
2. If I say that before firing you were moving at 20 kilometers per hour, is there any conceivable way for you to find out whether I'm speaking the truth or not? If there is, what is it?

I ask these questions to understand your thought process. If you don't find a satisfactory answer, that's fine, but in that case I would recommend you to explore what your lack of answer means for things you have said previously.

tsassi wrote:

TheDeathSummer wrote:

1. According to Newton's Third Law, every action has an equal and opposite reaction so, assuming I had the same weight as said bullet and I was stationary upon firing, after an hour I would be 1,000km's from the original firing point. 2,000km's from the bullet. Of course, we know the UNSC can seemingly ignore this law, as evidenced by ODP's not crashing into the planets they're protecting or scorching their surfaces with the required counter thrust, so in that case I'd still remain at the exact original firing point after a hour. Only as far away as I can move my limbs.

Oh, so, by the "original firing point", do you perhaps mean the center of mass of the bullet–you system? Because taking the center of mass as the origin is the only frame in this situation where Newton's third law applies.

tsassi wrote:

TheDeathSummer wrote:

But good, now that we hopefully have somewhat of a common understanding, would you be willing to agree that the 30 km/s is relative to the center of mass of the frigate–projectile system?

tsassi wrote:

TheDeathSummer wrote:

TheDeathSummer wrote:

It is a physics question. The only answer to it is either "yes" or "no".

Quote:

If I say that before firing you were moving at 20 kilometers per hour, is there any conceivable way for you to find out whether I'm speaking the truth or not? If there is, what is it?

tsassi wrote:

TheDeathSummer wrote:

In scenario 1, the exact moment the weapons officer clicked the "FIRE" button, a magical bubble with a circumference of 100 meters spawns into the universe and envelopes the end of the MAC barrel for a brief moment. When the frigate travels backwards and the MAC round travels forwards, the bubble remains almost exactly where it spawned, with nothing but the barrel or the round capable of entering or leaving it. The speed of the MAC round is in relation to the location of this bubble.

See, you need to help me out here. Because you've been reluctant to tell me what frame you are working in, I still don't know where your "exactly where it spawned" is. If it's the frigate's rest frame, your bubble remains attached to the frigate. If it's the center of mass frame of the frigate and projectile, then it slowly (in contrast to the projectile) drifts away from the frigate. If it's the rest frame of the testing facility, then it drifts away from the frigate however fast the frigate is drifting towards the facility.

This is what I'm trying to get you understand: you can't specify the location or speed of an object without specifying what frame, i.e., coordinate system, you are working in. I've tried to explain this to you. if you don't know what the term "inertial coordinate frame" means without looking it up, then I suggest you take this as a learning opportunity rather than as a debate, because at this point it's quite clear to me that you don't understand enough of the relevant physics to realize why I say the motion of the frigate is irrelevant, and why I keep saying that the points and bubble's you're talking about are not well defined.

I'd like to cooperate with you, but you need to realize that your understanding of physics isn't sufficient to meaningfully discuss this topic.

tsassi wrote:

TheDeathSummer wrote:

And I've already explained multiple times now that I'm using the original firing point as the reference point and, despite all that you've claimed and an irrelevant bottle analogy, you haven't actually explained why it's fallacious for me to do so. On the other hand, I still don't even know what you're arguing. It seems like you're just sitting on the fence, nitpicking, rather than actually standing on a hill and fighting for it. It's easy to never be proven wrong when you don't have an actual stance.

What I've been trying to help you understand is that the notions of velocity, and "being stationary" are relative to a given coordinate system. Furthermore, a point in physical space at any given time is only meaningfully defined relative to physical objects in that space at that time.

I'm genuinely not nitpicking. It's just that the things you're talking about—your original firing point, for example—are not well defined; they're ambiguous. With the information you have given me, I literally can not even in principle determine, say, what the position of your "original firing point" relative to the testing facility mentioned in the scene is. I try to give you the benefit of the doubt. Maybe you have something completely sensible in your head, but you just don't have the language to communicate it. But if you're not familiar with the fact that the velocity and motion of an object depends on the choice of coordinate system with respect to which they are measured and don't understand its implications to this discussion, we're going to have a hard time.

TheDeathSummer wrote:

If I'm so clueless, help me understand. Let's say the Commonwealth was travelling backwards at 35km/s (probably faster, but that's regardless), if the Commonwealth was stationary (or close enough to stationary) in Earths orbit and fired the same speed MAC at the Sun, what speed would it be travelling at (using the same reference point that you're using for the Chi Ceti scene)?

See, when you say "stationary in Earths orbit", do you mean a geostationary orbit where it always stays at the same point above the Earth's surface? Or do you mean that it's stationary relative to the fixed stars, i.e., if viewed from Earth, its location with respect to the stars would always appear the same, e.g., a little left and down from the Little Dipper? Since you're speaking of "orbit" my instinct would be that you mean a geostationary orbit, but how you phrased it is not how people generally phrase it.

I'm also not sure what you mean by "same speed MAC".

Just to check that I understand the rest of your question. You're asking me that if the Commonwealth was stationary near Earth (however you define "stationary" in this context), and fired a MAC round at the Sun at the same speed (as what?), how fast would the projectile be traveling (relative to what?)?

Really, to answer this question, I would need at least three pieces of information:

1. what you mean by stationary as discussed above
2. what is the distance between muzzle of the frigate and the projectile a certain amount of time (say a millisecond) after firing
3. what coordinate system are we measuring the speed relative to.

Without this information, it's impossible to answer your question. Also, in practice, you picked a system with possibly lots of parameters that might be relevant depending on the choice of coordinate system.