Physics questions

[EntAllat]

I've got a short action story that's been niggling at my brain for months now but I'm hesitant to commit it to bits and bytes because I'm not certain if the physics of it all isn't just pure fantasy. :-/ Unfortunately it's not something that I could simply get away with a bit of classic technobabble or even be vague about. It's front-and-center in the story and makes all the difference to the tension and the drama. Are there any knowledgeable types out there who could help me out with this?

Without giving away too much of the story itself here's the ideas that I'm struggling with:

1) Conservation of momentum.
Let's say that you have a small craft - I'm picturing something like a two person space version of a F22 Raptor - where movement is still created by thrust from fuel or rockets and not space-warping engines.

(a) What happens if you can no longer produce any thrust in any direction? Wouldn't the vehicle keep moving since there's no gravity or friction to slow it down?

(b) What if you still had one operational rocket that was stuck at a slight angle? Would it allow you to eventually move the vehicle around in a 180 degree arc so you were pointing in the opposite direction? Wouldn't each additional burst of energy to move in the right direction increase your speed because you don't have something opposing it?


2) "Energy shields" and human bodies.
Usually when we see energy shields used in combat in Trek, they encompass a large ship and seem to absorb the energy of photonic weapons while causing unshielded physical weapons like torpedoes break apart upon impact. Everyone inside the ship is protected (for the most part) from the kinetic energy of the impacts.

(a) What if the energy shield is around something smaller (like the aforementioned space version of a Raptor) and that smaller vehicle impacts a larger object that doesn't have shields? Would the smaller ship's shields be able to absorb enough of the kinetic energy of the impact to keep the people inside alive? (In a car wreck at high speeds, people die even if they don't get thrown through a window or some such because the internal organs keep trying to move forward when the rest of the body comes to that sudden stop. That can rip an aorta from the heart etc.)

(b) What would it look like? Would the smaller ship bounce back?

(c) What would it feel like? Can I plausibly say that a body in motion via a vehicle at high speeds that comes to a sudden and abrupt stop will survive because "the shields absorbed the energy" of the impact? Or is this an eye-rolling kind of fictional situation?

(d) Would any of this change if the larger object also had shields?

Opinions? I really want the physics of this one to be plausible.

[aadarshinah]

Well, I'd ask Elessar if you want things to be really acurate, but my two cents:

1) Conservation of momentum.
Let's say that you have a small craft - I'm picturing something like a two person space version of a F22 Raptor - where movement is still created by thrust from fuel or rockets and not space-warping engines.

(a) What happens if you can no longer produce any thrust in any direction? Wouldn't the vehicle keep moving, since there's no gravity or friction to slow it down?

(b) What if you still had one operational rocket that was stuck at a slight angle. Would it allow you to eventually move the vehicle around in a 180 degree arc so you were pointing in the opposite direction? Wouldn't each additional burst of energy to move in the right direction increase your speed because you don't have something opposing it?

As best I know, the ship will continue moving after thrust is lost until such a point something, such as friction, or a planet, or a torpedo, stops it. A single rocket, thrusting at an angle to the direction of motion, would, eventually, cause the ship to 180. But there would be a loss of momentum, so the ship would be travelling at a slower speed on the return trip than it did on the orginal course.

(a) What if the energy shield is around something smaller, like the aforementioned space version of a Raptor and it impacts a larger object, like a starship, that doesn't have shields? Would the smaller ship's shield's be able to absorb enough of the kinetic energy of the impact to keep the people inside alive?

Based on ST physics, I'd assume yes, so long as the sheild is strong enough to absorb the energy produced by such impact, that the ship/whatever retains integrity enough to support life (ie, life support still functions, and the sheild's energy generator, and the person isn't floating in open space inside a bubble)

(d) Would any of this change if the larger object also had shields?

Again, just guessing here, but I assume that an impact between two sheilded ships would be less strong than between two non-sheilded or 1-sheilded and one not-sheilded ship because there would be sheilds to absorb the energy produced, again providing the ships remain undamaged enough to support life.

For the ST version of what this would look like, I'd say take a look at Nemisis because, if I remember correctly, Enterprise either rams or come real close to ramming Scimitar. Though, thinking on it, the new Trek movie has a lot of ship-ship collisions and, best I can tell, it didn't make one iota of difference there if the ships were shielded or not what happened to them... But those were both high-speed, intended collisions, so presumabily they turned off the shields and incresed speed to make them as damaging as possible...

But, again, just my two cents.

[Silverbullet]

Whooo boy, that is a good question. I wonder what Ellesar comes up with.

I had wondered in similtude the Enterprise was travelling at Warp six when it hit the Magnetic anomoly and had a sudden stop. I would have thought that the ship would be torn apart and everyone inside turned to jelly. but I know squat about physics.

Hope you get a satisfactory answer.

[enterprikayak]

How would you stop the 180?

[aadarshinah]

turn off the rocket? that's the best I got.

[enterprikayak]

But then you'll just spin and spin.

[EntAllat]

How would you stop the 180?

That's a another problem - I think - but one I'm wanting to solve with some ingenuity on the part of the characters involved. At least, I think it's possible to do what I'm planning ... dang physics.

[aadarshinah]

How many rockets do you have available? 'cause if you've a second one, fire it with the same amount of thrust in the exact opposite direction of the first to cancel out the spin, and then shut them off at the same time. That should stop the spinning.

[Alelou]

I don't see how shields should that make much of a difference in a direct collision between two massive objects in space, especially if they are accelerating at the time. I would expect the smaller ship should be obliterated/the bigger ship damaged to a lesser degree, just as in any encounter on the highway.

I've always assumed that shields are designed to repel attacks that are primarily energetic in nature by absorbing/dispersing the energy. This might help protect from masses as well if they are small enough (stellar dust), but I also thought even in TNG starships still had to sweep ahead of them to get the dust and asteroids and such out of the way. Or maybe that's just an invention from my middle-aged brain's ya ya land? Because I also seem to recall the Bussard collector being on the front to collect antimatter particles. So I really don't remember.

[Enerdhil]

1) Conservation of momentum.
Let's say that you have a small craft - I'm picturing something like a two person space version of a F22 Raptor - where movement is still created by thrust from fuel or rockets and not space-warping engines.

(a) What happens if you can no longer produce any thrust in any direction? Wouldn't the vehicle keep moving since there's no gravity or friction to slow it down?

In real physics, yes. He only will change his status (both magnitude of speed and direction) if another force acts.

(b) What if you still had one operational rocket that was stuck at a slight angle? Would it allow you to eventually move the vehicle around in a 180 degree arc so you were pointing in the opposite direction? Wouldn't each additional burst of energy to move in the right direction increase your speed because you don't have something opposing it?

That's tricky, because the remaining rocket is on the vehicle. You will be able to change direction, because the exhaust gas particles (what leaves the rocket) will be compensated by the vehicle momentum (changing its direction and speed, depending on the thrust direction). But,
It will depend on the available energy (fuel) on the 'rocket'. To make a 180 turn, although possible, you will need enough fuel to change its original direction, slow down the speed along the original path to zero and reverse it. If we think about 'maneuvre' thrusters, probably no. Changing the nose of the vehicle to point in a reverse direction uses low energy (fuel) but still it will be moving at high speed along the original path, only with the rear pointing to the movement direction.

2) "Energy shields" and human bodies.
Usually when we see energy shields used in combat in Trek, they encompass a large ship and seem to absorb the energy of photonic weapons while causing unshielded physical weapons like torpedoes break apart upon impact. Everyone inside the ship is protected (for the most part) from the kinetic energy of the impacts.

(a) What if the energy shield is around something smaller (like the aforementioned space version of a Raptor) and that smaller vehicle impacts a larger object that doesn't have shields? Would the smaller ship's shields be able to absorb enough of the kinetic energy of the impact to keep the people inside alive? (In a car wreck at high speeds, people die even if they don't get thrown through a window or some such because the internal organs keep trying to move forward when the rest of the body comes to that sudden stop. That can rip an aorta from the heart etc.)

That's should be answered by ST Physics, not real one. The question of shielding is that, the shield may be able to stop the weapon (physical, quantum, photon) but the impact/explosion would be transfered (at least in momentum terms) to the vessel. So, a photonic torpedo should do almost the same damage hiting the vessel or the shield.

The only way the shield might absorb the impact is thinking of it as a 'viscous' agent, that will absorb the energy & momentum slowing it down before the hit on the vessel hull.

(b) What would it look like? Would the smaller ship bounce back?

In a real physics shield, yes. The hit to the shield would drive the raptor in the opposite direction, depending on the relative momentums. If the weapon momentum is more lower than that of the vessel, it may only slow it. But the vectorial (directions) are also important, like hiting a marble ball with another one.

(c) What would it feel like? Can I plausibly say that a body in motion via a vehicle at high speeds that comes to a sudden and abrupt stop will survive because "the shields absorbed the energy" of the impact? Or is this an eye-rolling kind of fictional situation?

That's St physics... In real world you would feel the shock. Probably would be dead after if the change in acceleration is hard. (about 3-5 g difference in acceleration is enough to cause death due to rupture of the spinal cord). You can find a similar argument in parachutes. Old WW-II parachutes had large changes in acceleration when opening. The change in acceleration (its called discomfort in physics & mechanics) could be too high and cause death (particularly if the user was not previously trained to use the chute).

The saucer of Enterprise-D on the movie, hiting the ground, would probably have killed all inside it...[/quote]

(d) Would any of this change if the larger object also had shields?

Opinions? I really want the physics of this one to be plausible.

Only in ST physics. Not in the real world physics. There is no difference in suffering a hit in the vessel herself or in her shields. Think about you wearing an old metallic medieval shield against an opponent using an iron ball (that one linked to a chain). If the ball hits the upper part of the shield, it will revolve around your arm, breaking it, and the shield will hit your head with a large kinetic energy (& momentum). If the ball hits the center of the shield, it will break your arm due to the impact and the whole shield will be pushed against your body. To reduce the effect, it would be necessary to you to gradually (but the time scale is short) lead your arm & shield backward but applying sufficient force in order to slow the effect of the ball, using muscle's power. It is easier against a light sword (one hand) but not against an iron ball.

[EntAllat]

Thank you Enerdhil!!

This made a lot of sense. Unfortunately it also means I can't quite do what I was thinking of doing. Not only would it be unbelievably implausible to survive in real world physics but it might not be believable even if the audience doesn't have a problem with ST physics. Drat.

1) Conservation of momentum.
Let's say that you have a small craft - I'm picturing something like a two person space version of a F22 Raptor - where movement is still created by thrust from fuel or rockets and not space-warping engines.

(a) What happens if you can no longer produce any thrust in any direction? Wouldn't the vehicle keep moving since there's no gravity or friction to slow it down?

In real physics, yes. He only will change his status (both magnitude of speed and direction) if another force acts.

That's what I thought. Everybody seems to confirm that, so at least that's good.

(b) What if you still had one operational rocket that was stuck at a slight angle? Would it allow you to eventually move the vehicle around in a 180 degree arc so you were pointing in the opposite direction? Wouldn't each additional burst of energy to move in the right direction increase your speed because you don't have something opposing it?

That's tricky, because the remaining rocket is on the vehicle. You will be able to change direction, because the exhaust gas particles (what leaves the rocket) will be compensated by the vehicle momentum (changing its direction and speed, depending on the thrust direction). But,
It will depend on the available energy (fuel) on the 'rocket'. To make a 180 turn, although possible, you will need enough fuel to change its original direction, slow down the speed along the original path to zero and reverse it. If we think about 'maneuvre' thrusters, probably no. Changing the nose of the vehicle to point in a reverse direction uses low energy (fuel) but still it will be moving at high speed along the original path, only with the rear pointing to the movement direction.

*facepalm* Oh, right. Dangit.

(c) What would it feel like? Can I plausibly say that a body in motion via a vehicle at high speeds that comes to a sudden and abrupt stop will survive because "the shields absorbed the energy" of the impact? Or is this an eye-rolling kind of fictional situation?

That's St physics... In real world you would feel the shock. Probably would be dead after if the change in acceleration is hard. (about 3-5 g difference in acceleration is enough to cause death due to rupture of the spinal cord). You can find a similar argument in parachutes. Old WW-II parachutes had large changes in acceleration when opening. The change in acceleration (its called discomfort in physics & mechanics) could be too high and cause death (particularly if the user was not previously trained to use the chute).

The saucer of Enterprise-D on the movie, hiting the ground, would probably have killed all inside it...

That's what I was afraid of. For the story to work the way I want it to the impact has to happen and has to be enormous but survivable. I just don't see any way to do that plausibly.

(d) Would any of this change if the larger object also had shields?

Opinions? I really want the physics of this one to be plausible.

Only in ST physics. Not in the real world physics. There is no difference in suffering a hit in the vessel herself or in her shields. Think about you wearing an old metallic medieval shield against an opponent using an iron ball (that one linked to a chain). If the ball hits the upper part of the shield, it will revolve around your arm, breaking it, and the shield will hit your head with a large kinetic energy (& momentum). If the ball hits the center of the shield, it will break your arm due to the impact and the whole shield will be pushed against your body. To reduce the effect, it would be necessary to you to gradually (but the time scale is short) lead your arm & shield backward but applying sufficient force in order to slow the effect of the ball, using muscle's power. It is easier against a light sword (one hand) but not against an iron ball.

That's a good analogy, thanks!

I'll think about this one some more, but I may have to scrap it. It just won't work.

[aadarshinah]

The saucer of Enterprise-D on the movie, hiting the ground, would probably have killed all inside it...

That's what I was afraid of. For the story to work the way I want it to the impact has to happen and has to be enormous but survivable. I just don't see any way to do that plausibly.

Ah, but here you have the wonders of inertial dampeners to play with. With ST physics, you can probably do anything if you make up a cool sounding science name for it.

[EntAllat]

The saucer of Enterprise-D on the movie, hiting the ground, would probably have killed all inside it...

That's what I was afraid of. For the story to work the way I want it to the impact has to happen and has to be enormous but survivable. I just don't see any way to do that plausibly.

Ah, but here you have the wonders of inertial dampeners to play with. With ST physics, you can probably do anything if you make up a cool sounding science name for it.

Good point. If I can make it sound like it's not such a cop out, it might still work.

[Kevin Thomas Riley]

^ Yeah, the fictional "inertial dampers" would work. In impact force would still be a gazillion times softer than the the crew would experience getting out of warp.

[aadarshinah]

Well, provided the inertial dampeners could be gaurenteed to provide the exact same force as you're currently experiencing in the exact opposite direction, what I remember of high school physics tells me that the forces should cancel out, making for a smooth ride.

Now, if you have a biology or chemistry question, those I can help you with.