?

tlb wrote:

Loren Pechtel wrote:But atmospheric pressure doesn't exist at the molecular level. It's just a bunch of molecules moving quite fast. That's what you're going to have to deflect. That's basically the same as the gravity field required to hold onto the atmosphere.

Pressure at the macro level can be related to kinetic energy density at the micro level, since it is the average force per unit area exerted on a plane by molecular collisions. As the pressure at sea level is set by gravity, you get the following effect: when air temperature increases or decreases (related to the average molecular kinetic energy) the air density decreases or increases in turn to keep the pressure constant.

PS: this is at the level of a room, trying to explain weather patterns of high and low pressure is more complicated; however it is still related to temperature.

You're not rebutting me at all. We experience pressure at the macro level, but at the micro level it's just the movement of molecules. Gravity is acting against the speed of the molecules heading towards the backstop and this is basically the same thing as a planet being able to drag back a molecule that is out in the thermosphere.

A good portion of the molecules in the atmosphere are moving faster than her slug thrower's bullets. You can't bounce those molecules without also bouncing the bullets.

Joat42 wrote:

Loren Pechtel wrote:But atmospheric pressure doesn't exist at the molecular level. It's just a bunch of molecules moving quite fast. That's what you're going to have to deflect. That's basically the same as the gravity field required to hold onto the atmosphere.

There is nothing to deflect since an air-molecule only have a miniscule amount of kinetic energy due to air-currents, if an air-molecule enters a gravity field it will be accelerated in the direction the field points to.

You're looking at the macro level. At the micro level those molecules are averaging 500m/s. That's faster than most handgun rounds.

tlb wrote:Yes, the kinetic energy of a single gas molecule is small, but its average speed is large; however the direction is mostly random, because of collisions with other molecules.

Hunter.CUNY.edu wrote:So the average speed of a gas molecule is about 500 m/sec.

The direction is random until you encounter the backstop. At that point a molecule that heads away from the backstop promptly bounces again but one that heads for it is going into vacuum and won't bounce. For any reasonably small angle to the normal from the backstop most of it's velocity will manifest in the direction of the backstop. Thus whatever is keeping the air off the backstop must exert enough force to overcome this.

Loren Pechtel wrote:You're not rebutting me at all. We experience pressure at the macro level, but at the micro level it's just the movement of molecules. Gravity is acting against the speed of the molecules heading towards the backstop and this is basically the same thing as a planet being able to drag back a molecule that is out in the thermosphere.

A good portion of the molecules in the atmosphere are moving faster than her slug thrower's bullets. You can't bounce those molecules without also bouncing the bullets.

True, not with a gravity field; as those apply acceleration regardless of mass.

However the Honorverse also has tractors (and pressors) and those appear to work on some non-gravitational principal -- because (unlike gravity) they don't apply the same acceleration to all items in their area of effect (see the interiors of the Masadan LACs towed through hyper in HotQ).
Since its effects are non-gravitational it may well apply different accelerations to items of different mass -- allowing one to be tuned to push away high velocity (but low kinetic energy) atmosphere molecules without also bouncing away (high kinetic energy) bullets or pulser darts.

Loren Pechtel wrote:You're looking at the macro level. At the micro level those molecules are averaging 500m/s. That's faster than most handgun rounds.

Sigh....

In a best case scenario at 1 atmosphere and at room temperature, excluding all other external factors, an air-molecule moves about 1cm/s on average. The 500m/s number is the speed it moves in a straight line until it runs into another molecule and bounces off in a new direction - ie a random walk in 3 dimensions and taking that into account we get the number I mentioned above.

The number I used can be calculated by using the size of an air-molecule, it's speed and the amount of other air-molecules present in a fixed volume with the assumption that they are fairly equidistant from each other.

Loren Pechtel wrote:But atmospheric pressure doesn't exist at the molecular level. It's just a bunch of molecules moving quite fast. That's what you're going to have to deflect. That's basically the same as the gravity field required to hold onto the atmosphere.

tlb wrote:Pressure at the macro level can be related to kinetic energy density at the micro level, since it is the average force per unit area exerted on a plane by molecular collisions. As the pressure at sea level is set by gravity, you get the following effect: when air temperature increases or decreases (related to the average molecular kinetic energy) the air density decreases or increases in turn to keep the pressure constant.

PS: this is at the level of a room, trying to explain weather patterns of high and low pressure is more complicated; however it is still related to temperature.

Loren Pechtel wrote:You're not rebutting me at all. We experience pressure at the macro level, but at the micro level it's just the movement of molecules. Gravity is acting against the speed of the molecules heading towards the backstop and this is basically the same thing as a planet being able to drag back a molecule that is out in the thermosphere.

A good portion of the molecules in the atmosphere are moving faster than her slug thrower's bullets. You can't bounce those molecules without also bouncing the bullets.

You are wrong, what the force changes is momentum: molecules have very high speed, but very low momentum, so it is NOT difficult for a force to change their direction. It is true that a bullet has a comparatively low speed; but its momentum is many orders of magnitude higher, so it is NOT reversed and penetrates through to the backstop.

Image the molecule were going a million times faster than the bullet; that seems a lot, but consider the the bullet has about Avogadro's number times as much mass and you can begin to see the difference in momentum.

Jonathan_S wrote:

Loren Pechtel wrote:You're not rebutting me at all. We experience pressure at the macro level, but at the micro level it's just the movement of molecules. Gravity is acting against the speed of the molecules heading towards the backstop and this is basically the same thing as a planet being able to drag back a molecule that is out in the thermosphere.

A good portion of the molecules in the atmosphere are moving faster than her slug thrower's bullets. You can't bounce those molecules without also bouncing the bullets.

True, not with a gravity field; as those apply acceleration regardless of mass.

However the Honorverse also has tractors (and pressors) and those appear to work on some non-gravitational principal -- because (unlike gravity) they don't apply the same acceleration to all items in their area of effect (see the interiors of the Masadan LACs towed through hyper in HotQ).
Since its effects are non-gravitational it may well apply different accelerations to items of different mass -- allowing one to be tuned to push away high velocity (but low kinetic energy) atmosphere molecules without also bouncing away (high kinetic energy) bullets or pulser darts.

I have figured tractor beams caused issues because the field isn't perfectly flat. Simple, present-day example of the issue: If you put two spacecraft next to each other in Earth's orbit they will drift apart. This is not simply Heisenberg at work, they will actually be pulled away from each other because Earth's gravitational field drops off with distance rather than being perfectly flat. (The effect happens no matter what body you are orbiting, it's just that it happens much faster orbiting a planet than a star. It's the gradient that matters.)

Joat42 wrote:

Loren Pechtel wrote:You're looking at the macro level. At the micro level those molecules are averaging 500m/s. That's faster than most handgun rounds.

Sigh....

In a best case scenario at 1 atmosphere and at room temperature, excluding all other external factors, an air-molecule moves about 1cm/s on average. The 500m/s number is the speed it moves in a straight line until it runs into another molecule and bounces off in a new direction - ie a random walk in 3 dimensions and taking that into account we get the number I mentioned above.

The number I used can be calculated by using the size of an air-molecule, it's speed and the amount of other air-molecules present in a fixed volume with the assumption that they are fairly equidistant from each other.

But there's nothing to bump into in the vacuum you're trying to create next to the backstop. Thus the 500 m/s number is the relevant one, not the 1 cm/sec.

tlb wrote:

Loren Pechtel wrote:You're not rebutting me at all. We experience pressure at the macro level, but at the micro level it's just the movement of molecules. Gravity is acting against the speed of the molecules heading towards the backstop and this is basically the same thing as a planet being able to drag back a molecule that is out in the thermosphere.

A good portion of the molecules in the atmosphere are moving faster than her slug thrower's bullets. You can't bounce those molecules without also bouncing the bullets.

You are wrong, what the force changes is momentum: molecules have very high speed, but very low momentum, so it is NOT difficult for a force to change their direction. It is true that a bullet has a comparatively low speed; but its momentum is many orders of magnitude higher, so it is NOT reversed and penetrates through to the backstop.

Image the molecule were going a million times faster than the bullet; that seems a lot, but consider the the bullet has about Avogadro's number times as much mass and you can begin to see the difference in momentum.

Galileo has something to say about this. Objects fall at the same speed regardless of mass. The proposal was to use a gravity field to keep the air off the backstop. Such a field will impart a fixed m/s to everything entering it regardless of mass. Thus the greater momentum of the bullet doesn't matter.

tlb wrote:You are wrong, what the force changes is momentum: molecules have very high speed, but very low momentum, so it is NOT difficult for a force to change their direction. It is true that a bullet has a comparatively low speed; but its momentum is many orders of magnitude higher, so it is NOT reversed and penetrates through to the backstop.

Image the molecule were going a million times faster than the bullet; that seems a lot, but consider the the bullet has about Avogadro's number times as much mass and you can begin to see the difference in momentum.

Loren Pechtel wrote:Galileo has something to say about this. Objects fall at the same speed regardless of mass. The proposal was to use a gravity field to keep the air off the backstop. Such a field will impart a fixed m/s to everything entering it regardless of mass. Thus the greater momentum of the bullet doesn't matter.

The force exerted by a NATURAL gravity field is indeed dependent on the mass of the object being moved, so you are correct for that case. However an artificial field set up to repel, something that is of shorter effect than the inverse of R squared, need not be linearly dependent on mass and therefore can be affected by the momentum of the object that is to be repelled.

It should be obvious that the repeller field should be very short range and be more effective on air than bullets. I do not know why you have a problem with this, when you seemed to accept that Star Wars could have a box that levitated the box of a wagon and yet did no work (so did not require an energy input).

PS: Although the backstop is made of focused gravity forces, we do not really know what creates a repeller field (we know they have them, but regular gravity does not repel; so what is it? We may have called it a gravity field, but it is not necessarily something that would recognized by Galileo.).