A physics question for fantasy application!

[ImNotTrevor]

Hey all, I figured this is the right place to ask this:
So I'm working on a fantasty/magitech/western mashup thing of a world. And I came up with a simple concept:
Loadstones.
Basically a rock or similar enchanted with the ability to increase its weight. (I imagine by increasing its density since they don't grow at all when this happens) Really useful for counterweights.

I then had the idea of "what would happen if someone made a bunch of tiny Loadstones to use as bullets/shotgun pellets?

So the question is this:
How would a bullet or buckshot pellet behave if, upon leaving the barrel, it became 10x heavier? (Discarding that this is impossible in our universe without accelerating to some fraction of C, which isn't what is happening) Would it drastically lose velocity and peter out? Would it be as effective as I imagined? Does physics have no answer at all and I'm a crazy person for even asking this?

Something instinctual tells me it will be the first or third option.

[Knaight]

It depends on which conservation rules you're keeping around. Notably:

• Conservation of Momentum: The projectile is now moving one tenth as fast.
• Conservation of Energy (only kinetic): The projectile is now moving one root-tenth as fast.
• Conservation of Energy (kinetic and potential): You're hosed. The absence of conservation of mass creates a reference frame issue, where depending on where you put the frame you get different results for projectile speed while not getting different results for other speeds. It breaks down terribly, and as such isn't an option. An increase in potential energy that goes with the mass is assumed.
• Conservation of Momentum + Conservation of Energy (only kinetic): The projectile is now moving one tenth as fast. That drops it to one one hundredth the original kinetic energy, which means that 9/100 needs to go somewhere. With collisions this is pretty easy to solve (deformation), but there's not really a single obvious way for energy to be lost from the projectile. I'd go with either it heating or production of sound.

For weapons, these behaviors are mostly useless. The one exception is if you can trigger the effect much later, launching something high in the air and cranking the mass up at the peak. It creates a pretty weird flight path, but there's also room for it to be a very dangerous falling object.

[Peelee]

Well, assuming spherical cow in a vacuum, a projectile that magically increases weight after being ejected would behave like any normal projectile.

v = v₀ + at

v² = v₀² + 2aΔx

Δx = v₀t + 1/2 at

Δx = vt - 1/2 at²

Velocity, time, distance, and gravity are all unchanged by mass.

[ImNotTrevor]

It depends on which conservation rules you're keeping around. Notably:

• Conservation of Momentum: The projectile is now moving one tenth as fast.
• Conservation of Energy (only kinetic): The projectile is now moving one root-tenth as fast.
• Conservation of Energy (kinetic and potential): You're hosed. The absence of conservation of mass creates a reference frame issue, where depending on where you put the frame you get different results for projectile speed while not getting different results for other speeds. It breaks down terribly, and as such isn't an option. An increase in potential energy that goes with the mass is assumed.
• Conservation of Momentum + Conservation of Energy (only kinetic): The projectile is now moving one tenth as fast. That drops it to one one hundredth the original kinetic energy, which means that 9/100 needs to go somewhere. With collisions this is pretty easy to solve (deformation), but there's not really a single obvious way for energy to be lost from the projectile. I'd go with either it heating or production of sound.

For weapons, these behaviors are mostly useless. The one exception is if you can trigger the effect much later, launching something high in the air and cranking the mass up at the peak. It creates a pretty weird flight path, but there's also room for it to be a very dangerous falling object.

I figured so. I'll probably list it as an experiment someone did but it didn't really work out like they hoped.

The other option is to say "it's magic, I aint gotta explain (expletive)" but that's less fun.

[Lord Torath]

Since this is magic, you could always assume that velocity is conserved during the magic mass multiplication, rather than energy or momentum, in which case your bullet will hit with... 10² times the original kinetic energy? Which would be really nasty.

[Peelee]

Since this is magic, you could always assume that velocity is conserved during the magic mass multiplication, rather than energy or momentum, in which case your bullet will hit with... 10² times the original kinetic energy? Which would be really nasty.

That's more or less what I was trying to get at. Keep it stupidly simple, and just change the damage die. Fantasy games just aren't really built for the strict application of physics.

It's nowhere near a correct answer, but it just needs to be correct enough for the players to have fun and not mind.

[ImNotTrevor]

Weirdly, this isn't for a game. Lol.

Though I suppose the setting would be good for one

[Peelee]

Weirdly, this isn't for a game. Lol.

Though I suppose the setting would be good for one

Then I'd say to use Knaight's answer. I'm simplifying way more than probably needed.

[FreddyNoNose]

I figured so. I'll probably list it as an experiment someone did but it didn't really work out like they hoped.

The other option is to say "it's magic, I aint gotta explain (expletive)" but that's less fun.

Can you make it such that the 10X happens after it enters the body of whatever you hit with it?

[ImNotTrevor]

Can you make it such that the 10X happens after it enters the body of whatever you hit with it?

Would that mean anything? Most of the energy is spent by that point. I guess it would be good if you were trying to weigh someone down by filling them with bullets?

[gomipile]

It depends on which conservation rules you're keeping around. Notably:

• Conservation of Momentum: The projectile is now moving one tenth as fast.
• Conservation of Energy (only kinetic): The projectile is now moving one root-tenth as fast.
• Conservation of Energy (kinetic and potential): You're hosed. The absence of conservation of mass creates a reference frame issue, where depending on where you put the frame you get different results for projectile speed while not getting different results for other speeds. It breaks down terribly, and as such isn't an option. An increase in potential energy that goes with the mass is assumed.
• Conservation of Momentum + Conservation of Energy (only kinetic): The projectile is now moving one tenth as fast. That drops it to one one hundredth the original kinetic energy, which means that 9/100 needs to go somewhere. With collisions this is pretty easy to solve (deformation), but there's not really a single obvious way for energy to be lost from the projectile. I'd go with either it heating or production of sound.

For weapons, these behaviors are mostly useless. The one exception is if you can trigger the effect much later, launching something high in the air and cranking the mass up at the peak. It creates a pretty weird flight path, but there's also room for it to be a very dangerous falling object.

None of those make intuitive sense to me, since they all break Galilean relativity in this situation. The key question is, "The projectile is now moving one [...] as fast" relative to what? If you use the reference frame of the launch mechanism, you're still breaking conservation of momentum and kinetic energy relative to the planet's core, the sun, the galaxy's center, etc.

I'd say that it makes more sense for all of the conservation laws go out the window and to preserve relativity of reference frames instead.

Incidentally, the weapons in Mass Effect work nearly exactly like the OP was hoping. The difference is that an external effect is used to lower the mass of a metal projectile while it's inside the barrel, not a property of the projectile itself.

[Knaight]

None of those make intuitive sense to me, since they all break Galilean relativity in this situation. The key question is, "The projectile is now moving one [...] as fast" relative to what? If you use the reference frame of the launch mechanism, you're still breaking conservation of momentum and kinetic energy relative to the planet's core, the sun, the galaxy's center, etc.

There's no real way out of that causing a problem, but you can at least preserve them for the special case where the launch mechanism is effectively stationary.

[NichG]

If you imagine the case of a snowball flying through a snow storm, it's not too dissimilar from this setup, and no physical laws need to be broken to figure out what happens. In that case, there is actually a correct second reference frame - that of the falling snow - and by calculating the inelastic collision between the snowball and the new snow to be added you can figure out what happens to the momentum and how much energy is dissipated (in inelastic deformation of the snowball and surrounding snow, sound, and heat).

Which is basically, its velocity adjusts towards the average velocity of the material reservoir. At the same time, kinetic energy decreases as it is converted into other forms of energy. Potential energy isn't an issue because the mass is being added from a supply which is at the same position in space as the thing to which the mass is being added (you don't collide with snowflakes far above or below you) - it's just that that mass field doesn't normally interact with other matter, and your fantasy elements are toggling that interaction on and off to adjust the mass of the bullet.

This would mostly only help weaponize things if your 'mass field' had a high relative velocity to the surface of the planet. In that case, if you're shooting in a particular direction, you could massively speed up the shot or increase its impact. But if you're shooting the other way, the bullet would suddenly zip around and strike you instead - so that'd be very situational. Firing upwards and turning the coupling to the mass field on at the height of the arc seems like it should work, but whatever your mass field is made of has to have some reason to be up there despite the ground being a lower energy state for it gravitationally (for example, like air, it could be pressurized), so you might end up having to pay as much energy to e.g. compress the mass field down as you would gain in gravitational potential energy by adding the mass to the bullet. Still, that might be an efficient way to convert some sort of non-kinetic energy source into kinetic energy.

[Lazymancer]

So the question is this:
How would a bullet or buckshot pellet behave if, upon leaving the barrel, it became 10x heavier? (Discarding that this is impossible in our universe without accelerating to some fraction of C, which isn't what is happening) Would it drastically lose velocity and peter out? Would it be as effective as I imagined? Does physics have no answer at all and I'm a crazy person for even asking this?

Something instinctual tells me it will be the first or third option.

However intuitive aether is ("default" frame of reference), it is not recognized as viable hypothesis for over a century. Consequently, nothing in modern physic justifies the idea of object "slowing down" - there is no "default state" to which object should decelerate. Any speed it could have is only "speed relative to something".


I'd say correct answer is #2.

If we ignore impossibility to parse this within the realm of modern physics, we'd better limit "impossibility" to minimum. Consequenly, position (as time/space vector; i.e. speed) of the object should remain the same - unlike momentum it is not a derived characteristic.

Moreover, even if we attempt to "preserve" momentum, what momentum would that be? Which frame of reference should we choose to preserve momentum in?

Let's say we have this Loadstone simply lying on the ground.
Relative to someone standing nearby speed is 0.
Relative to Sun speed is ~30 kilometers per second.

If mass increases, what frame of reference should we choose to preserve the momentum in? In what frame of reference will the speed decelerate? If it is Sun-based, "deceleration" of Loadstone would mean attempt at escape velocity during sunset (my guess is it will burn in the atmosphere).

[Peelee]

However intuitive aether is ("default" frame of reference), it is not recognized as viable hypothesis for over a century. Consequently, nothing in modern physic justifies the idea of object "slowing down" - there is no "default state" to which object should decelerate. Any speed it could have is only "speed relative to something".


I'd say correct answer is #2.

If we ignore impossibility to parse this within the realm of modern physics, we'd better limit "impossibility" to minimum. Consequenly, position (as time/space vector; i.e. speed) of the object should remain the same - unlike momentum it is not a derived characteristic.

Moreover, even if we attempt to "preserve" momentum, what momentum would that be? Which frame of reference should we choose to preserve momentum in?

....the localized system, dude. That's what's having the most effect on the object.

[Lazymancer]

....the localized system, dude. That's what's having the most effect on the object.

I'm not fully understanding the point you are trying to make here.

What should happen to the Loadstone being at rest on a moving wagon?

[Peelee]

I'm not fully understanding the point you are trying to make here.

What should happen to the Loadstone being at rest on a moving wagon?

It stays at rest. It's not being acted on by a net external force. If it's a projectile, then it is being acted upon by a net external force. That's kind of the crux of the entire problem here.

[Lazymancer]

It stays at rest. It's not being acted on by a net external force. If it's a projectile, then it is being acted upon by a net external force. That's kind of the crux of the entire problem here.

In what frame of reference does it stay at rest?

[Peelee]

In what frame of reference does it stay at rest?

Again, the localized system. I'm not sure what part of this is confusing you. It's very, very basic.

[Knaight]

Again, the localized system. I'm not sure what part of this is confusing you. It's very, very basic.

Localized is a bit vague - is it the wagon? Is it the ground? In your case it appears to be the wagon (as otherwise the wagon would slow), but there are inherent ambiguities there. With that said, using a reference frame of a stationary observer on the earth nearby can get consistent results pretty easily.

[ImNotTrevor]

In what frame of reference does it stay at rest?

I think this is overcomplicating the problem. Apply Occam's Razor. The simplest system between the firer and the fired-upon for my bullet application will do just fine for the math. I don't feel the need to get into Relativity over a potentially-neato bullet trick.

[FreddyNoNose]

Would that mean anything? Most of the energy is spent by that point. I guess it would be good if you were trying to weigh someone down by filling them with bullets?

It would cause damage by changing size.

[Lazymancer]

With that said, using a reference frame of a stationary observer on the earth nearby can get consistent results pretty easily.

As long as aetheric Loadstone remains close to Earth. If such Loadstone is above geostationary orbit, increase of mass would accelerate it and make it fly away from Earth.

And even close to ground we can observe counter-intuitive behaviour: falling Loadstone slows down if mass is increased.

I think this is overcomplicating the problem. Apply Occam's Razor. The simplest system between the firer and the fired-upon for my bullet application will do just fine for the math. I don't feel the need to get into Relativity over a potentially-neato bullet trick.

Unless you are going to apply laws in only one set of circumstances, you'll have accommodate all.

Either way, physics-breaking behaviour could function in any number of ways. Imo, method #2 causes the least amount of questions (like when does one "natural" frame of reference end and the other begin).

[Peelee]

Localized is a bit vague - is it the wagon? Is it the ground? In your case it appears to be the wagon (as otherwise the wagon would slow), but there are inherent ambiguities there. With that said, using a reference frame of a stationary observer on the earth nearby can get consistent results pretty easily.

Yeah, I used it because of its vagueness. A rock at rest on a wagon? Loke you said, system is the rock and wagon. As for the opening question, I'd call the system the target and loadstone (already moving at an initial v).

When the purpose of an application is trivial (not the best word here. No offense to the op), I tend to simplify to the bare minimum of what I think is needed. I'm also aware that what I think and what others think may not match up.

It would cause damage by changing size.

Size doesn't change, only mass.

As long as aetheric Loadstone remains close to Earth. If such Loadstone is above geostationary orbit, increase of mass would accelerate it and make it fly away from Earth.

Knowing virtually nothing about the OP's intended world, i feel reasonably safe saying he won't be worried about any height that would meaningfully affect it.

Unless you are going to apply laws in only one set of circumstances, you'll have accommodate all.

This is one of the most ridiculous things I've ever heard. There's no reason to accommodate every set of circumstances, and in almost all likelihood the application will only be for a small number of circumstances. I mean, you could accommodate every possible circumstanve but why even bother?

I choose to believe you aren't being deliberately obtuse, which means you're just needlessly complicating matters.

[ImNotTrevor]

It would cause damage by changing size.

But they don't get any bigger. (Or minimally so. Too small to make a difference.)

They increase in density, ostensibly from drawing matter from "Elsewhere." (This is the technical term for the unknown location from which this mass comes and goes, but that's neither here nor there)

But yeah. They don't increase in size, they get heavier. Which I guess increases their density and heat.

In response to above:
I mean, we're talking about fantasy/magitech western here. The situation and application is fairly trivial, since this is for fun, and I only want it to make intuitive sense without relying on "becuz it kewl."

And no, due to being a pretty much wild-west setting with some industrial revolution-esque magitech laying around, I am not anticipating anything going into geosynchronous orbit at any point in the
Application of Loadstones. Except maybe a very unfortunate squirrel subject to an unusually cruel trap involving a very large Loadstone and a lever of remarkable strength. (Sidenote: Does it count as derailing my own thread if I make it clear that I would be very amused by anyone who could tell me how heavy a Loadstone would need to be in order to put a squirrel into orbit by sheer cartoonish lever-launching? This definitely won't make it into the fiction but the thought amuses me.)

[Lord Torath]

But they don't get any bigger. (Or minimally so. Too small to make a difference.)

They increase in density, ostensibly from drawing matter from "Elsewhere." (This is the technical term for the unknown location from which this mass comes and goes, but that's neither here nor there)

But yeah. They don't increase in size, they get heavier. Which I guess increases their density and heat.

In response to above:
I mean, we're talking about fantasy/magitech western here. The situation and application is fairly trivial, since this is for fun, and I only want it to make intuitive sense without relying on "becuz it kewl."

And no, due to being a pretty much wild-west setting with some industrial revolution-esque magitech laying around, I am not anticipating anything going into geosynchronous orbit at any point in the
Application of Loadstones. Except maybe a very unfortunate squirrel subject to an unusually cruel trap involving a very large Loadstone and a lever of remarkable strength. (Sidenote: Does it count as derailing my own thread if I make it clear that I would be very amused by anyone who could tell me how heavy a Loadstone would need to be in order to put a squirrel into orbit by sheer cartoonish lever-launching? This definitely won't make it into the fiction but the thought amuses me.)

Just guessing, here, but I suspect if you had enough force to overcome the air resistance to get the poor thing into orbit, the drag forces involved would tear the poor thing apart.

[ahenobarbi]

It depends on which conservation rules you're keeping around. Notably:

• Conservation of Momentum: The projectile is now moving one tenth as fast.
• Conservation of Energy (only kinetic): The projectile is now moving one root-tenth as fast.
• Conservation of Energy (kinetic and potential): You're hosed. The absence of conservation of mass creates a reference frame issue, where depending on where you put the frame you get different results for projectile speed while not getting different results for other speeds. It breaks down terribly, and as such isn't an option. An increase in potential energy that goes with the mass is assumed.
• Conservation of Momentum + Conservation of Energy (only kinetic): The projectile is now moving one tenth as fast. That drops it to one one hundredth the original kinetic energy, which means that 9/100 needs to go somewhere. With collisions this is pretty easy to solve (deformation), but there's not really a single obvious way for energy to be lost from the projectile. I'd go with either it heating or production of sound.

For weapons, these behaviors are mostly useless. The one exception is if you can trigger the effect much later, launching something high in the air and cranking the mass up at the peak. It creates a pretty weird flight path, but there's also room for it to be a very dangerous falling object.

They're all extremely useful! Just decrease mass 10x after accelerating the projectile instead of increasing it.

Also those loadstones would be nice for making Perpetual Motion Machines of 1st kind (outputting work without taking any energy) (at least until pesky physicist come around and discover where they're getting energy from).

[Lazymancer]

This is one of the most ridiculous things I've ever heard. There's no reason to accommodate every set of circumstances, and in almost all likelihood the application will only be for a small number of circumstances. I mean, you could accommodate every possible circumstanve but why even bother?

I choose to believe you aren't being deliberately obtuse, which means you're just needlessly complicating matters.

Needless complication is a necessity to try and evaluate dominant influence on the Loadstone to determine proper frame of reference within which it will act - every single time it is used.

Only geocentric frame of reference is semi-consistitent within regular circumstances. Though, I suspect there might be flaming bolts involved - deceleration implies acceleration under different circumstances. Unless, of course, additional set of rules will be created to prevent that bit from getting needlessly complicated.

Does it count as derailing my own thread if I make it clear that I would be very amused by anyone who could tell me how heavy a Loadstone would need to be in order to put a squirrel into orbit by sheer cartoonish lever-launching? This definitely won't make it into the fiction but the thought amuses me.

Rough estimate: if Loadstone intially weighs the same as squirrel, falls from sufficiently high place to reach 10m/s and lever is cartoonishly perfect in all respects, then Loadstone would need to increase it's mass 1,000 times (to deliver 10 km/s of dV necessary for LEO). If realistic factors are introduced, up to tenfold increase might be required.

The squirrel has to be pretty hardcore, though. Regular squirrels moving at speeds exceeding Mach 20 tend to evaporate (either due to air drag or aerodynamic heating) - that's like shuttle re-entry in reverse, except much worse - begins in dense layers of atmosphere. Though, IRL squirrels are pretty safe: IRL levers will break.

[Peelee]

Needless complication is a necessity to try and evaluate dominant influence on the Loadstone to determine proper frame of reference within which it will act - every single time it is used.

Counter-argument: why?

[ImNotTrevor]

They're all extremely useful! Just decrease mass 10x after accelerating the projectile instead of increasing it.

Also those loadstones would be nice for making Perpetual Motion Machines of 1st kind (outputting work without taking any energy) (at least until pesky physicist come around and discover where they're getting energy from).

The energy for the tranfer of mass comes from the caster. It takes effort for them to change the weight, up or down. For this reason they've not solved any real energy issues. Your spellcaster only has so much juice per day. The enchantments on the Loadstone take time, and don't supply the energy. They just make it simpler.
(Kinda like how the layout of your computer helps it to do tasks for you, but the energy to do say tasks doesn't come from the computer itself.)