Silly supersonic question
Discussion
Do radio signals travel at the speed of sound?
If so how would an aircraft travelling at supersonic speed tell the airport it was on the way? It would arrive at the same time or before the radio signal.
And if you radioed as you got going and then went twice the speed of sound you would be able to overtake the message.
Told you it was a stupid question.
If so how would an aircraft travelling at supersonic speed tell the airport it was on the way? It would arrive at the same time or before the radio signal.
And if you radioed as you got going and then went twice the speed of sound you would be able to overtake the message.
Told you it was a stupid question.
Edited by BMWChris on Thursday 22 July 17:03
Did you fall asleep in Physics?
Sound is progated through a medium - such as air or water. It's speed varies depending on the density of that medium but rarely exceeds 700 mph or so.
As has been already said, light is altogether different. It is electromagnetic by nature and travels at much higher speeds, 186,000 mile per second in a vacuum. If it passes through a medium, such as air or water, this speed will be affected but not by enough to make a noticeable difference to a casual observer.
So, an object travelling twice the speed of sound is stil,l travelling WAY below the speed of light.
Sensitive equipment WILL however, pick up the change in radio frequency caused by the aircraft's inherent speed. Indeed, many radar systems use this phenomenon to gauge the speed of an incoming contact.
Sound is progated through a medium - such as air or water. It's speed varies depending on the density of that medium but rarely exceeds 700 mph or so.
As has been already said, light is altogether different. It is electromagnetic by nature and travels at much higher speeds, 186,000 mile per second in a vacuum. If it passes through a medium, such as air or water, this speed will be affected but not by enough to make a noticeable difference to a casual observer.
So, an object travelling twice the speed of sound is stil,l travelling WAY below the speed of light.
Sensitive equipment WILL however, pick up the change in radio frequency caused by the aircraft's inherent speed. Indeed, many radar systems use this phenomenon to gauge the speed of an incoming contact.
Edited by Eric Mc on Thursday 22 July 17:34
Eric Mc said:
Did you fall asleep in Physics?
Sound is progated through a medium - such as air or water. It's speed varies depending on the density of that medium but rarely exceeds 700 mph or so.
As has been already said, light is altogether different. It is electromagnetic by nature and travels at much higher speeds, 186,000 mile per second in a vacuum. If it passes through a medium, such as air or water, this speed will be affected but not by enough to make a noticeable difference to a casual observer.
So, an object travelling twice the speed of sound is stil,l travelling WAY below the speed of light.
Sensitive equipment WILL however, pick up the change in radio frequency caused by the aircraft's inherent speed. Indeed, many radar systems use this phenomenon to gauge the speed of an incoming contact.
Yep called pulse/doppler radar, no doubt Gin 15 will be here in a second, but the set uses a mode where the velocity of the target return is used to track it to great effect.......Sound is progated through a medium - such as air or water. It's speed varies depending on the density of that medium but rarely exceeds 700 mph or so.
As has been already said, light is altogether different. It is electromagnetic by nature and travels at much higher speeds, 186,000 mile per second in a vacuum. If it passes through a medium, such as air or water, this speed will be affected but not by enough to make a noticeable difference to a casual observer.
So, an object travelling twice the speed of sound is stil,l travelling WAY below the speed of light.
Sensitive equipment WILL however, pick up the change in radio frequency caused by the aircraft's inherent speed. Indeed, many radar systems use this phenomenon to gauge the speed of an incoming contact.
Edited by Eric Mc on Thursday 22 July 17:34
Eric Mc said:
If it passes through a medium, such as air or water, this speed will be affected but not by enough to make a noticeable difference to a casual observer.
That's really not right.To the casual observer, it's going to appear as if the propagating radio wave has stopped in it's tracks. Certainly in water.
To the more refined observer, who actually goes out to inspect the behaviour in the cloud, or the sea, then it will become apparent that the wave has been scattered, and has elevated the temperature of the water that it hit.
In practice, only very low frequency transmissions can penetrate water.
Very high frequency transmissions sometimes barely penetrate air, let alone water.
As the frequency changes, different behaviours are experienced with propagation in different materials.
Free space is just that, like outer space. It's the only one where noticeable differences are hard to find.
Edited by dilbert on Thursday 22 July 18:39
Mr E said:
dilbert said:
Eric Mc said:
If it passes through a medium, such as air or water, this speed will be affected but not by enough to make a noticeable difference to a casual observer.
That's really not right.dilbert said:
Eric Mc said:
If it passes through a medium, such as air or water, this speed will be affected but not by enough to make a noticeable difference to a casual observer.
That's really not right.To the casual observer, it's going to appear as if the propagating radio wave has stopped in it's tracks. Certainly in water.
To the more refined observer, who actually goes out to inspect the behaviour in the cloud, or the sea, then it will become apparent that the wave has been scattered, and has elevated the temperature of the water that it hit.
In practice, only very low frequency transmissions can penetrate water.
Very high frequency transmissions sometimes barely penetrate air, let alone water.
As the frequency changes, different behaviours are experienced with propagation in different materials.
Free space is just that, like outer space. It's the only one where noticeable differences are hard to find.
Edited by dilbert on Thursday 22 July 18:39
What causes light to split up when passed through a prism?
I'm genuinely asking - I thought it was because the medium affected the constituent elements of the light because of the way the different frequencies were affected by the medium in different ways).
Mojocvh said:
the set uses a mode where the velocity of the target return is used to track it to great effect.......
Velocity or frequency? The speed of light is a constant.Eric Mc said:
What causes light to refract in water?
What causes light to split up when passed through a prism?
I'm genuinely asking - I thought it was because the medium affected the constituent elements of the light because of the way the different frequencies were affected by the medium in different ways).
I think there's a confusion between speed and intensity. Light will get diffused and absorbed, but it still travels at the same speed, it doesn't start slowing down if the water is a bit murky for example.What causes light to split up when passed through a prism?
I'm genuinely asking - I thought it was because the medium affected the constituent elements of the light because of the way the different frequencies were affected by the medium in different ways).
As I understand it PD RADARS rely on the fact that a moving target, that has a coming towards you or moving away from you vector, causes a Doppler shift in the wavelength of the returned target signal compared to the other returns, and it is this that allows them to break a target out from the ground clutter (because the ground isn't moving). Thus giving you the option of 'Look Down/Shoot Down'.
A counter to a PD RADAR is to turn on a 90 degree track to the interceptor - there is now no Doppler shift and the target a/c disappears.
Obviously it's a wee bit more complex in real life.
A counter to a PD RADAR is to turn on a 90 degree track to the interceptor - there is now no Doppler shift and the target a/c disappears.
Obviously it's a wee bit more complex in real life.
Eric Mc said:
dilbert said:
Eric Mc said:
If it passes through a medium, such as air or water, this speed will be affected but not by enough to make a noticeable difference to a casual observer.
That's really not right.To the casual observer, it's going to appear as if the propagating radio wave has stopped in it's tracks. Certainly in water.
To the more refined observer, who actually goes out to inspect the behaviour in the cloud, or the sea, then it will become apparent that the wave has been scattered, and has elevated the temperature of the water that it hit.
In practice, only very low frequency transmissions can penetrate water.
Very high frequency transmissions sometimes barely penetrate air, let alone water.
As the frequency changes, different behaviours are experienced with propagation in different materials.
Free space is just that, like outer space. It's the only one where noticeable differences are hard to find.
Edited by dilbert on Thursday 22 July 18:39
What causes light to split up when passed through a prism?
I'm genuinely asking - I thought it was because the medium affected the constituent elements of the light because of the way the different frequencies were affected by the medium in different ways).
Using such simple concepts, along with things like polarisation, it is possible to make surprisingly accurate calculations on the magnitude and polarisation of the transmitted and reflected waves. All that need be known is the magnitude, frequency and polarisation of the incident wave, the physical size and the basic electrical properties of the material.
For a physicist, it's much deeper.
A physicist is interested in nuclear fluorescence, bremsstrahlung radiation, electron spins, and quantum jumps of electrons in their shells. For the electronics engineer, the radio signal is a beam in the ether. It has power and physical dimensions. For the physicist the radio signal is a stream of photons. Each of which will interact with an atomic nucleus.
In truth, I'd say there's a fairly distinct divide between the higher level electronic view, and the lower level physical view. Both are the same thing but Physics is much more focussed, whereas electronics is looking at the world as (more of) a whole.
Diffraction occurs in certain materials because of the way an electromagnetic wave interacts with the materials. A material that has slits cut into it, could be made of plastic, or it could be made of metal. The plastic is transparent so the waves pass through. There is little difference between the slits and the actual grating.
Where the material is metal, the important consideration is how the material interacts with the incident wave. There are various different factors that constrain the way in which the wave on the other side of the grating behaves.
If you think about an antenna, it's an important thing to think about how the electrons in the wire stimulate the photons that travel through the sky. It is important to realise that electromagnetic waves are photons, and not electrostatic or electromagnetic fields. The field decays with the cube of the distance, whereas the wave, decays with the square of the distance. Nevertheless, the photons have their own smaller field. The coupling between co-located antennas is direct. When remotely coupled, the coupling is indirect.
A closely coupled antenna can drain power from the transmitter. A remotely coupled one cannot. This is because of the near/far field behaviours. It demonstrates that a photon has it's own separate propagation field, completely independent of the induction field. This induction field, is the same as that found in things like motors. There really is no difference between the coils of a motor, and an antenna. It's just the way they are used, and what actually happens to the energy.
In the area immediately around the antenna is the induction field. The induction field interacts with the energetic photons that stream away from the antenna. I don't know for sure (it's probably a PhD) but I'd wager that the induction field has the greatest effect in the atomic nuclei that are emitting the photons. In the region around the antenna, is a zone of progressive equilibrium. The same is true for the diffraction grating. In this zone, lie local energetic maxima and minima. At increasing distance from the antenna it becomes difficult to differentiate a between an isotropic radiator with those parameters, and a diffraction grating or an antenna with synthetic properties.
Materials themselves can exhibit diffraction grating behaviours. It is the key method by which x-ray crystallography is done. This is a technique that can be used to identify the spacing and position of individual atoms within a crystal structure. It was around well before the electron microscope. Importantly, the photons, and electrons bounce off the atomic nuclei in a characteristic way. Something like a marble in a pin box.
Refraction uses similar mechanisms. There photons are typically less likely to excite electrons into action. Nevertheless there are still interactions between the atoms. The slowing of the waves at the discontinuity affects the spatial distribution of the energy in time.
In truth, radio isn't waves or particles. It's just perturbations in space and time. If you change the stiffness of the space, then the distribution of the energy will change in time. After that, it's just a numbers game.
Edited by dilbert on Thursday 22 July 19:33
Edited by dilbert on Thursday 22 July 19:42
Simpo Two said:
Mojocvh said:
the set uses a mode where the velocity of the target return is used to track it to great effect.......
Velocity or frequency? The speed of light is a constant.- in a vacuuum*. Light can be much slower through a different medium.
Simpo Two said:
Eric Mc said:
What causes light to refract in water?
What causes light to split up when passed through a prism?
I'm genuinely asking - I thought it was because the medium affected the constituent elements of the light because of the way the different frequencies were affected by the medium in different ways).
I think there's a confusion between speed and intensity. Light will get diffused and absorbed, but it still travels at the same speed, it doesn't start slowing down if the water is a bit murky for example.What causes light to split up when passed through a prism?
I'm genuinely asking - I thought it was because the medium affected the constituent elements of the light because of the way the different frequencies were affected by the medium in different ways).
For example;
1. Air, only slightly less than c, speed is 0.9997 of c.
2. water 0.75 of c.
3. fused quartz 0.686 of c.
4. crown glass* 0.658 of c.
5. dense flint glass* 0.60 of c.
6. diamond, approx 0.41 of c.
edit for quotes
Edited by Mr E on Thursday 22 July 19:34
Mr E said:
Simpo Two said:
Velocity or frequency? The speed of light is a constant.
- in a vacuuum*. Light can be much slower through a different medium.
Mr E said:
Nope, it slows down - hence the odd optical effects (refractive index is the ratio of C / SOL in that medium)
For example;
1. Air, only slightly less than c, speed is 0.9997 of c.
2. water 0.75 of c.
3. fused quartz 0.686 of c.
4. crown glass* 0.658 of c.
5. dense flint glass* 0.60 of c.
6. diamond, approx 0.41 of c.
That would imply that if you put enough diamonds together, the photons will eventually stop and can be swept up with a brush and dustpan...For example;
1. Air, only slightly less than c, speed is 0.9997 of c.
2. water 0.75 of c.
3. fused quartz 0.686 of c.
4. crown glass* 0.658 of c.
5. dense flint glass* 0.60 of c.
6. diamond, approx 0.41 of c.
If you have a stationary photon is it still light? Can you see it?
Edited by Simpo Two on Thursday 22 July 22:38
Simpo Two said:
Mr E said:
Simpo Two said:
Velocity or frequency? The speed of light is a constant.
- in a vacuuum*. Light can be much slower through a different medium.
Mr E said:
Nope, it slows down - hence the odd optical effects (refractive index is the ratio of C / SOL in that medium)
For example;
1. Air, only slightly less than c, speed is 0.9997 of c.
2. water 0.75 of c.
3. fused quartz 0.686 of c.
4. crown glass* 0.658 of c.
5. dense flint glass* 0.60 of c.
6. diamond, approx 0.41 of c.
That would imply that if you put enough diamonds together, the photons will eventually stop and can be swept up with a brush and dustpan...For example;
1. Air, only slightly less than c, speed is 0.9997 of c.
2. water 0.75 of c.
3. fused quartz 0.686 of c.
4. crown glass* 0.658 of c.
5. dense flint glass* 0.60 of c.
6. diamond, approx 0.41 of c.
If you have a stationary photon is it still light? Can you see it?
Edited by Simpo Two on Thursday 22 July 22:38
comadies said:
Simpo Two said:
Mr E said:
Simpo Two said:
Velocity or frequency? The speed of light is a constant.
- in a vacuuum*. Light can be much slower through a different medium.
Mr E said:
Nope, it slows down - hence the odd optical effects (refractive index is the ratio of C / SOL in that medium)
For example;
1. Air, only slightly less than c, speed is 0.9997 of c.
2. water 0.75 of c.
3. fused quartz 0.686 of c.
4. crown glass* 0.658 of c.
5. dense flint glass* 0.60 of c.
6. diamond, approx 0.41 of c.
That would imply that if you put enough diamonds together, the photons will eventually stop and can be swept up with a brush and dustpan...For example;
1. Air, only slightly less than c, speed is 0.9997 of c.
2. water 0.75 of c.
3. fused quartz 0.686 of c.
4. crown glass* 0.658 of c.
5. dense flint glass* 0.60 of c.
6. diamond, approx 0.41 of c.
If you have a stationary photon is it still light? Can you see it?
Edited by Simpo Two on Thursday 22 July 22:38
They are absorbed and re-radiated throughout. The exact method varies depending on the material. A piece of glass, like a prism, you can see the light in the glass, when you can't see the light in the air.
Importantly, when an optical material is super cooled, the light can be caused to slow considerably. A vacuum has almost no "temperature", and yet light passes easily. This leads to the conclusion that the photons are interacting with the optical material as they pass through.
The cooling did not slow the passage of the photons, but it did slow the interactions between the photons and the matter.
Edited by dilbert on Thursday 22 July 23:48
Simpo Two said:
Mr E said:
Simpo Two said:
Velocity or frequency? The speed of light is a constant.
- in a vacuuum*. Light can be much slower through a different medium.
Mr E said:
Nope, it slows down - hence the odd optical effects (refractive index is the ratio of C / SOL in that medium)
For example;
1. Air, only slightly less than c, speed is 0.9997 of c.
2. water 0.75 of c.
3. fused quartz 0.686 of c.
4. crown glass* 0.658 of c.
5. dense flint glass* 0.60 of c.
6. diamond, approx 0.41 of c.
That would imply that if you put enough diamonds together, the photons will eventually stop and can be swept up with a brush and dustpan...For example;
1. Air, only slightly less than c, speed is 0.9997 of c.
2. water 0.75 of c.
3. fused quartz 0.686 of c.
4. crown glass* 0.658 of c.
5. dense flint glass* 0.60 of c.
6. diamond, approx 0.41 of c.
If you have a stationary photon is it still light? Can you see it?
Edited by Simpo Two on Thursday 22 July 22:38
There. Physics with a capital 'PH'.
The rules that model the behaviour of light and electrons (and thus model _all_ of optics, _all_ of chemistry ... pretty much everything except radioactivity and gravity) are best explained by the theory of quantum electro-dynamics, known as QED. If anyone is interested in an astonishingly thorough, yet short and very readable explanation of the theory (that doesn't require advanced maths but genuinely captures its key features), get a copy of QED by Richard Feynman .. published by Penguin Books. It's drawn up from four lectures he aimed at a public, non-specialist audience. He got a Nobel Prize for establishing the theory of QED, and he was a brilliant teacher. And handy on the bongos.
Bugger me, just found some videos of the lecture series. Try these for size:
http://vega.org.uk/video/subseries/8
Bugger me, just found some videos of the lecture series. Try these for size:
http://vega.org.uk/video/subseries/8
Edited by ATG on Friday 23 July 00:05
ATG said:
The rules that model the behaviour of light and electrons (and thus model _all_ of optics, _all_ of chemistry ... pretty much everything except radioactivity and gravity) are best explained by the theory of quantum electro-dynamics, known as QED. If anyone is interested in an astonishingly thorough, yet short and very readable explanation of the theory (that doesn't require advanced maths but genuinely captures its key features), get a copy of QED by Richard Feynman .. published by Penguin Books. It's drawn up from four lectures he aimed at a public, non-specialist audience. He got a Nobel Prize for establishing the theory of QED, and he was a brilliant teacher. And handy on the bongos.
Bugger me, just found some videos of the lecture series. Try these for size:
http://vega.org.uk/video/subseries/8
I've started watching that, and just part of the first lecture is simply superb.Bugger me, just found some videos of the lecture series. Try these for size:
http://vega.org.uk/video/subseries/8
Edited by ATG on Friday 23 July 00:05
Ginetta G15 Girl said:
As I understand it PD RADARS rely on the fact that a moving target, that has a coming towards you or moving away from you vector, causes a Doppler shift in the wavelength of the returned target signal compared to the other returns, and it is this that allows them to break a target out from the ground clutter (because the ground isn't moving). Thus giving you the option of 'Look Down/Shoot Down'.
A counter to a PD RADAR is to turn on a 90 degree track to the interceptor - there is now no Doppler shift and the target a/c disappears.
Obviously it's a wee bit more complex in real life.
A counter to a PD RADAR is to turn on a 90 degree track to the interceptor - there is now no Doppler shift and the target a/c disappears.
Obviously it's a wee bit more complex in real life.
that's it! moves into the ground return velocity. The thing that always gets me is how the sets utilise monopulse tracking, in practice a sublime system, but how did someone work it out both in theory and prove it mathematically WOW!
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