You've got it backwards. Coloumb is defined as c = a*s, while Ampere is defined as the constant current that will produce an attractive force of 2 × 10^–7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum.
Coloumb, as a unit, is derived fra Ampere. Furthermore, Coloumb is a measure of charge, not electrons, in the same way that Ampere is a measure of current, not electrions/s. If you know that your current results from a stream of electrons, instead of say, ions, protons, or positrons, then you can calculate the corresponding electrons/s.
It seems they were, but catching fabricated results like these isn't exactly easy and it won't happen in the review process.
In order to catch fabricated results you'd either have to repeat the experiment, which nobody wanted to do since the research was low impact, or catch discrepancies in the data, which was how he was caught out.
If you mean the "popping noise" the TM65 engine that Copenhagen Suborbitals testet made at startup, then it was a bit of engine oscilations. It's most likely caused by the engine being run at a low fuel pressure. The fuel will ignite in the ignition chamber, causing the pressure to rise, giving a higher exhaust flow, causing the pressure to drop, giving less exhaust flow, resulting in more fuel in the ignition chamber, that ignites,...
At higher fuel pressures the oscilations are dampened. (But they do sound awsome!)
I don't know if that's the case with SpaceX's Falcon, but I'm pretty sure that if they have engine oscilations it's nothing they can't handle.
When I get paid enough to cover my needs I don't really care about money. If I had to choose between two jobs: one with huge pay and dreary work, and another with adequete pay and interesting work, I'd go for the second job.
Well, sort of. It's all engine research. And I hope that we'll continue doing research, even if we get a working space plane. There's allways more to learn, new discoveries to be made, system to optimize.
What makes the Skylon concept different is the engine. Instead of a SCRAM-jet air breathing engines they're going for a traditional rocket engine that is fed pressurized air, while in the atmosphere. This is advantageus to the SCRAM-jet and rocket approach, since only a single engine is needed for getting into orbit.
I'm not sure I believe in the Skylon space plane, but the SABRE engine is definitly interesting. If nothing else, researching the concept will teach us something about what is possible with our current technology.
While what you say about Galilean invariance is true, it has no implication on the current discussion. For each inertial frame you only have one acceleration per ridgid body.
Your words were:
If I have Ftot = F1 + F2, then I can say that atot = Ftot/m, or I can say that a1 = F1/m and a2 = F2/m and atot = a1 + a2.
a1 and a2 are accelerations the body experiences. Like forces, they add as vectors to get a net result. It's as valid as talking about the forces adding. If you think there's no component acceleration, then that's equivalent to saying that there's no component force, only a net force. Well, in a sense you could say that a rigid body can only experience one net force. But to then go "what do you mean forces, plural?" would be to miss the broader perspective.
Clearly you were talking about the "accelerations" in one inertial frame, not in multiple. So sorry, but you can't weasel yourself out of this discussion by refering to Galilean invariance.
Now, let's use the above on your example: Me sitting on a chair. According to you there is an acceleration from the pull of gravity, a1(t) = -9.8 m/s^2, and an acceleration from my chair, a2(t) = 9.8 m/s^2, and we can sum these to get the "resulting acceleration": 0 m/s^2. So far so good. What you say seems to work.
But, since I have two "accelerations" a direct consequence is that I will have two distinct "positions". A position at p1(t) = -1/2*9.8 m/s^*t^2 and a position at p2(t) = 1/2*9.8 m/s^*t^2. (In the same inertial frame!) At the moment I am still sitting on my chair. My position is neither above my chair nor below it, so what you claim is still wrong.
Yeah, SpaceX are cheap. If I remember correctly, then the cost to low earth orbit in the last sattellite launch I was involved in was something like $12 - $14k/kg.
I'm not convinced that a pioneering effort would really be that beneficial, but that doesn't mean I'm not all for it. If for nothing else, then just to see how far we (as a race) can go.
Grandparent isn't talking about unobtainium, but ordinary resources not in this gravity well. The cost of getting something into orbit is prohibitively high, in the neighbourhood of $10000/kg.
This is high school physics, more specifically Newton's laws of motion. It's not as if this is really that hard to understand:
First Law:
The velocity of a body remains constant unless the body is acted upon by an external force.
Second Law:
The acceleration a of a body is parallel and directly proportional to the net force F and inversely proportional to the mass m, i.e., F = ma.
Thrid Law:
The mutual forces of action and reaction between two bodies are equal, opposite and collinear.
Nowhere in Newton's laws of motion do I find any mention of "net acceleration" or "accelerations" (plural), but let's for a moment assume you're right.
Acceleration is defined as the rate of change of velocity, dv/dt, so, each of these "accelerations" will result in "velocities" (again plural), and using the definition for velocity, i.e., rate of change of position, or dp/dt, we get multiple positions. So, a direct consequence of your "accelerations" is "positions" (plural!), all for the same mass! I've never observed anything like that, nor have I ever heard of anybody observing it. If you have any evidence of this, I'd very much like to see it.
Now, it can be advantageous to calculate the acceleration of a body by summing the individual forces divided by the mass of the body. But that's all it is. A computational trick. There is no such thing as "accelerations".
It's rather easy to infer the acceleration from the resulting force (and mass). But why do you keep talking about "accelerations" (plural)? A ridgid body can only have one acceleration. (As the grandparent previously correctly stated.)
Did you factor in the conversion from energy bound in the fuel to kinetic energy of the car?
If your didn't, then with a conventional four stroke engine you get about 30% efficiency, so petrol is only about four times better than a battery, while with a PEM fuel cell you can get efficiency up to about 50%, making hydrogen 1 to 1.5 times better than batteries.
And that's just by volume. Even though volume certaintly factors in, I'm not convinced there isn't more, e.g. weight, to the problem of energy storage.
That is a consequence of the Danish education system. Education is free in Denmark, and in addition students automatically receive a stipend large enough to support them through the education. This results in danes having quite high levels of education. For example, commonly an ordinary programmer holds a master's degree.
Because of this, it can be quite hard for people without at least the equivalent of a bachelors degree to get a job.
While I do like that you're using SI-units, I find myself being a bit pedantic about your choice of units. Thrust is force, and therefore measured in Newton [N], not kg.
The derivative of acceleration is called jerk, and is indeed the measurement used for measuring ride quality, at least when comparing cruise controllers.
If you read what you posted, you'll notice the following:
How does it work?
Magnetic Ride Control is made possible by the development of magneto-rheological (MR) fluid located inside the monotube shock dampers. The fluid is a suspension of magnetically soft, tiny iron particles in a synthetic hydrocarbon-based solution. The fluid's consistency can be manipulated through the precise application of electronic current, resulting in continuously variable, real-time damping. In fact, the development of MR fluid is so significant that medical researchers have adapted it for use in high-tech prosthetic devices, such artificial knees.
In other words, the technology used in your car is not comparable to the technology discussed in the article, with the exception that both technologies use active instead of passive dampening.
Satellites are usually lifted to their orbit by a launch vehicle. Normally they don't do any extensive manuvering using thrusters.
Thrusters on satellites are used primarily for attitude control. If the satellite is in low earth orbit attitude control can be performed without using thruster. For example, ISS was designed for attitude control using thruster, but zero-propellant manouvers is possible.
Slashdot Mirror
You've got it backwards. Coloumb is defined as c = a*s, while Ampere is defined as the constant current that will produce an attractive force of 2 × 10^–7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum.
Coloumb, as a unit, is derived fra Ampere. Furthermore, Coloumb is a measure of charge, not electrons, in the same way that Ampere is a measure of current, not electrions/s. If you know that your current results from a stream of electrons, instead of say, ions, protons, or positrons, then you can calculate the corresponding electrons/s.
Still, you're right that GP is wrong.
Indeed I would.
It seems they were, but catching fabricated results like these isn't exactly easy and it won't happen in the review process.
In order to catch fabricated results you'd either have to repeat the experiment, which nobody wanted to do since the research was low impact, or catch discrepancies in the data, which was how he was caught out.
And to add to your list: High speed simulations of dynamical systems, metereology, numerical optimization, ...
Basically, grab any engineering/hard science subject you can think of, and they'll run simulations.
If you mean the "popping noise" the TM65 engine that Copenhagen Suborbitals testet made at startup, then it was a bit of engine oscilations. It's most likely caused by the engine being run at a low fuel pressure. The fuel will ignite in the ignition chamber, causing the pressure to rise, giving a higher exhaust flow, causing the pressure to drop, giving less exhaust flow, resulting in more fuel in the ignition chamber, that ignites, ...
At higher fuel pressures the oscilations are dampened. (But they do sound awsome!)
I don't know if that's the case with SpaceX's Falcon, but I'm pretty sure that if they have engine oscilations it's nothing they can't handle.
Well, sort of, yes.
When I get paid enough to cover my needs I don't really care about money. If I had to choose between two jobs: one with huge pay and dreary work, and another with adequete pay and interesting work, I'd go for the second job.
And, wire wrapping was at that time better at handling vibrations and bumps than solder. Perfect for avionics!
Oh, I miss wire wrapping.
Well, sort of. It's all engine research. And I hope that we'll continue doing research, even if we get a working space plane. There's allways more to learn, new discoveries to be made, system to optimize.
What makes the Skylon concept different is the engine. Instead of a SCRAM-jet air breathing engines they're going for a traditional rocket engine that is fed pressurized air, while in the atmosphere. This is advantageus to the SCRAM-jet and rocket approach, since only a single engine is needed for getting into orbit.
I'm not sure I believe in the Skylon space plane, but the SABRE engine is definitly interesting. If nothing else, researching the concept will teach us something about what is possible with our current technology.
While what you say about Galilean invariance is true, it has no implication on the current discussion. For each inertial frame you only have one acceleration per ridgid body.
Your words were:
If I have Ftot = F1 + F2, then I can say that atot = Ftot/m, or I can say that a1 = F1/m and a2 = F2/m and atot = a1 + a2.
a1 and a2 are accelerations the body experiences. Like forces, they add as vectors to get a net result. It's as valid as talking about the forces adding. If you think there's no component acceleration, then that's equivalent to saying that there's no component force, only a net force. Well, in a sense you could say that a rigid body can only experience one net force. But to then go "what do you mean forces, plural?" would be to miss the broader perspective.
Clearly you were talking about the "accelerations" in one inertial frame, not in multiple. So sorry, but you can't weasel yourself out of this discussion by refering to Galilean invariance.
Now, let's use the above on your example: Me sitting on a chair. According to you there is an acceleration from the pull of gravity, a1(t) = -9.8 m/s^2, and an acceleration from my chair, a2(t) = 9.8 m/s^2, and we can sum these to get the "resulting acceleration": 0 m/s^2. So far so good. What you say seems to work.
But, since I have two "accelerations" a direct consequence is that I will have two distinct "positions". A position at p1(t) = -1/2*9.8 m/s^*t^2 and a position at p2(t) = 1/2*9.8 m/s^*t^2. (In the same inertial frame!) At the moment I am still sitting on my chair. My position is neither above my chair nor below it, so what you claim is still wrong.
Yeah, SpaceX are cheap. If I remember correctly, then the cost to low earth orbit in the last sattellite launch I was involved in was something like $12 - $14k/kg.
You're welcome!
I'm not convinced that a pioneering effort would really be that beneficial, but that doesn't mean I'm not all for it. If for nothing else, then just to see how far we (as a race) can go.
SpaceX: Falcon 9 Pricing information
Grandparent isn't talking about unobtainium, but ordinary resources not in this gravity well. The cost of getting something into orbit is prohibitively high, in the neighbourhood of $10000/kg.
This is high school physics, more specifically Newton's laws of motion. It's not as if this is really that hard to understand:
First Law: The velocity of a body remains constant unless the body is acted upon by an external force. Second Law: The acceleration a of a body is parallel and directly proportional to the net force F and inversely proportional to the mass m, i.e., F = ma. Thrid Law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear.Nowhere in Newton's laws of motion do I find any mention of "net acceleration" or "accelerations" (plural), but let's for a moment assume you're right.
Acceleration is defined as the rate of change of velocity, dv/dt, so, each of these "accelerations" will result in "velocities" (again plural), and using the definition for velocity, i.e., rate of change of position, or dp/dt, we get multiple positions. So, a direct consequence of your "accelerations" is "positions" (plural!), all for the same mass! I've never observed anything like that, nor have I ever heard of anybody observing it. If you have any evidence of this, I'd very much like to see it.
Now, it can be advantageous to calculate the acceleration of a body by summing the individual forces divided by the mass of the body. But that's all it is. A computational trick. There is no such thing as "accelerations".
It's rather easy to infer the acceleration from the resulting force (and mass). But why do you keep talking about "accelerations" (plural)? A ridgid body can only have one acceleration. (As the grandparent previously correctly stated.)
Just to be a unit-pedant: Acceleration is measured in m/s^2. (or other equivalent distance per time squared measure)
Did you factor in the conversion from energy bound in the fuel to kinetic energy of the car?
If your didn't, then with a conventional four stroke engine you get about 30% efficiency, so petrol is only about four times better than a battery, while with a PEM fuel cell you can get efficiency up to about 50%, making hydrogen 1 to 1.5 times better than batteries.
And that's just by volume. Even though volume certaintly factors in, I'm not convinced there isn't more, e.g. weight, to the problem of energy storage.
But why would you build a power plant like that?
You're proposing a cycle that goes something like:
solar mirrors -> zinc reactor -> hydrogen furnace -> turbine
Why not just use the old and tried method of:
solar mirrors -> hot steam -> turbine
It would be simpler and far more efficient.
Now, the story is interesting because it's about creating hydrogen using sunlight, without converting the sunlight to electricity first.
That is a consequence of the Danish education system. Education is free in Denmark, and in addition students automatically receive a stipend large enough to support them through the education. This results in danes having quite high levels of education. For example, commonly an ordinary programmer holds a master's degree. Because of this, it can be quite hard for people without at least the equivalent of a bachelors degree to get a job.
While I do like that you're using SI-units, I find myself being a bit pedantic about your choice of units. Thrust is force, and therefore measured in Newton [N], not kg.
The derivative of acceleration is called jerk, and is indeed the measurement used for measuring ride quality, at least when comparing cruise controllers.
How does it work?
Magnetic Ride Control is made possible by the development of magneto-rheological (MR) fluid located inside the monotube shock dampers. The fluid is a suspension of magnetically soft, tiny iron particles in a synthetic hydrocarbon-based solution. The fluid's consistency can be manipulated through the precise application of electronic current, resulting in continuously variable, real-time damping. In fact, the development of MR fluid is so significant that medical researchers have adapted it for use in high-tech prosthetic devices, such artificial knees.
In other words, the technology used in your car is not comparable to the technology discussed in the article, with the exception that both technologies use active instead of passive dampening.
Satellites are usually lifted to their orbit by a launch vehicle. Normally they don't do any extensive manuvering using thrusters.
Thrusters on satellites are used primarily for attitude control. If the satellite is in low earth orbit attitude control can be performed without using thruster. For example, ISS was designed for attitude control using thruster, but zero-propellant manouvers is possible.