Speed C is Dependant Upon Source?

[terrabyte]

for lasers too?

that's fascinating...

 

[nautica]

For the "kiddies" or "kiddoes" of this board, I found this site for you which may help explain it a little more on your level (I only say this b/c your argument sounds like that of my 10 year old son.)

It sounds like you must enjoy science and be relatively intelligent since you are in AP classes. But it appears you are to busy arguing over semantics instead of learning from the people on this board.

Nautica

 

[Chronos]

Pitcher throws photon to mirror. Mirror hands photon to umpire. Umpire discards it and and hands new photon to mirror. Mirror tosses new photon back to pitcher.

 

[Alkatran]

I just thought of something. Take an object and accelerate it to .8c and then let it go about a constant velocity. Right when that object reaches .8c and light beam next to it wille mitt. How fast will that light beam be going with respect to the object. If the speed of light does not change, would it be c? I don't think it would c. I don't know though. Maybe there is a way around this paradox.

In this scenario you have two observers. Observer B is moving at .8c according to observer A. Observer A sees ("sees" being used as a loose term, as you can't see a photon at a distance) the photon moving away at c and B moving away at .8c. For A the speed between the photon and B is .2c.

FRAME SWITCH!

B sees the photon moving away at c and A moving the other direction at .8c. For B the speed between the photon and A is 1.8c.

How can this possibly be true? That's what the theory of special relativity covers. B is moving through (space-)time at a different rate than A and B's space is contracted according to A (A's is contracted according to B).

In fact, something that happens at the same time for A will NOT happen at the same time for B.


For some reason I get the feeling we're about to be back to arguing with RAM1024 and GeistKessel over this... only their names have changed and they're a few years younger...

 

[russ_watters]

Pitcher throws photon to mirror. Mirror hands photon to umpire. Umpire discards it and and hands new photon to mirror. Mirror tosses new photon back to pitcher.

Outstanding.

 

[russ_watters]

I just thought of something. Take an object and accelerate it to .8c and then let it go about a constant velocity. Right when that object reaches .8c and light beam next to it wille mitt. How fast will that light beam be going with respect to the object. If the speed of light does not change, would it be c? I don't think it would c. I don't know though. Maybe there is a way around this paradox. [emphasis added]

Yes. Its called Special Relativity. It states that the speed of light is constant for all observers regardless of their inertial frame of reference and that the laws of the universe are the same everywhere.

 

[BobG]

Solar Radiation Pressure. For high altitude satellites, the overall perturbations are so small that the solar radiation pressure begins to become a significant factor affecting satellite orbits.

Light hitting a highly reflective surface exerts a force on the satellite. Light hitting an absorbant surface exerts an even smaller force on the satellite.

I've taken this as a given without worrying to much about the details, but this discussion kind of piques my curiosity about why this happens.

It would seem to me that, in the interests of energy conservation, absorbant materials would change the momentum more than reflective materials.

Any comments on why the actual behavior is so counter-intuitive?

Oops! Edited to remove inaccurate statement - totally absorbant materials still receive some force from light energy, just less.

Actual equation is:

F=\frac{F_sA}{cm}(1+q)cosi

where F_s is solar pressure or 1367 \frac{W}{m^2}
c is speed of light
m is mass of satellite
q is reflectivity (1 for totally reflective, 0 for totally absorbant)
i is incidence angle

On an asymetrical satellite design, similar to the NOAA GOES weather satellite, the torque from solar pressure would be in the range of 5.54 x 10^-4 Newton meters. Small, but still the largest factor affecting satellite attitude.

 

[Doc Al]

Radiation Pressure

Light hitting a highly reflective surface causes a small change in the satellite's momentum.

Right.

Light hitting an absorbant surface causes an even smaller momentum change in the satellite

Right.

(a totally absorbant surface would impart no momentum change to the satellite).

Says who?

It would seem to me that, in the interests of energy conservation, absorbant materials would change the momentum more than reflective materials.

Any comments on why the actual behavior is so counter-intuitive?

It's no different than bouncing a ball against a wall. The ball has incoming momentum +p. If it bounces back (like a superball), then it's final momentum will be -p, so \Delta p = -2p. If it's absorbed (like a putty ball), then the final momentum is 0 (assume a massive wall) and \Delta p = -p. The ball that bounces off transfers more momentum to the wall that the one that sticks.

 

[BobG]

Right.

Right.

Says who?

It's no different than bouncing a ball against a wall. The ball has incoming momentum +p. If it bounces back (like a superball), then it's final momentum will be -p, so \Delta p = -2p. If it's absorbed (like a putty ball), then the final momentum is 0 (assume a massive wall) and \Delta p = -p. The ball that bounces off transfers more momentum to the wall that the one that sticks.

Makes sense as long as I stay on the surface. The photons being absorbed by atoms and then released adds some confusion factor.

But, when I think about it, it could be thought of as the photon's kinetic energy has been converted to potential energy when the electron level is raised. When the electron falls back into its original orbit, the potential is reconverted back to kinetic energy.

 

[Alkatran]

Solar Radiation Pressure. For high altitude satellites, the overall perturbations are so small that the solar radiation pressure begins to become a significant factor affecting satellite orbits.

Light hitting a highly reflective surface exerts a force on the satellite. Light hitting an absorbant surface exerts an even smaller force on the satellite.

I've taken this as a given without worrying to much about the details, but this discussion kind of piques my curiosity about why this happens.

It would seem to me that, in the interests of energy conservation, absorbant materials would change the momentum more than reflective materials.

Any comments on why the actual behavior is so counter-intuitive?

Oops! Edited to remove inaccurate statement - totally absorbant materials still receive some force from light energy, just less.

Actual equation is:

F=\frac{F_sA}{cm}(1+q)cosi

where F_s is solar pressure or 1367 \frac{W}{m^2}
c is speed of light
m is mass of satellite
q is reflectivity (1 for totally reflective, 0 for totally absorbant)
i is incidence angle

On an asymetrical satellite design, similar to the NOAA GOES weather satellite, the torque from solar pressure would be in the range of 5.54 x 10^-4 Newton meters. Small, but still the largest factor affecting satellite attitude.

It's pushed more because the reflective surface not only takes the photon hit, it gets pushed by the photon taking off in the other direction.

 

[quantumdude]

i still disagree. i mean a photon is energy right?

No: A photon has energy. A photon is not to be identified with energy.

well if the energy isn't destroyed then the photon isn't destroyed.

The energy is not destroyed, but the photon is. It has to be in order for the atom to attain the higher energy state.

maybe stewarta is correct. maybe the photon gets stopped by the mirror and then the photon is accelerated at c, back off the mirror.

This cannot be, because EM fields (the only thing around that can possibly exert appreciable forces on things) do not interact with photons.

 

[BobG]

Makes sense as long as I stay on the surface. The photons being absorbed by atoms and then released adds some confusion factor.

But, when I think about it, it could be thought of as the photon's kinetic energy has been converted to potential energy when the electron level is raised. When the electron falls back into its original orbit, the potential is reconverted back to kinetic energy.

I take back the comment about thinking it made some sense.

If the satellite were massive and did not move, it would make sense. The light leaves with the same amount of energy it left with. The fact that the satellite does move due to solar pressure means some of the energy has been transferred to the satellite.

I'm having trouble figuring out how everything balances out.

Of course, the energy of light depends not upon its speed, which is constant, but upon its intensity and frequency. So, if the satellite moves away from the light source, the light reflected must be emitted at a lower frequency than it had when it first struck the surface.

Close?

 

[Alkatran]

I take back the comment about thinking it made some sense.

If the satellite were massive and did not move, it would make sense. The light leaves with the same amount of energy it left with. The fact that the satellite does move due to solar pressure means some of the energy has been transferred to the satellite.

I'm having trouble figuring out how everything balances out.

Of course, the energy of light depends not upon its speed, which is constant, but upon its intensity and frequency. So, if the satellite moves away from the light source, the light reflected must be emitted at a lower frequency than it had when it first struck the surface.

Close?

Sounds right, the photoelectric effect and all that.

 

[russ_watters]

If the satellite were massive and did not move, it would make sense. The light leaves with the same amount of energy it left with. The fact that the satellite does move due to solar pressure means some of the energy has been transferred to the satellite.

I'm having trouble figuring out how everything balances out.

Take a speed and reverse it, you get -v. Since the energy equation includes v^2, the minus signs cancel out and you get the exact same energy as you had before, but in the opposite direction.

Momentum, on the other hand, has just v...

 

[Chronos]

It's no different than bouncing a ball against a wall. The ball has incoming momentum +p. If it bounces back (like a superball), then it's final momentum will be -p, so \Delta p = -2p. If it's absorbed (like a putty ball), then the final momentum is 0 (assume a massive wall) and \Delta p = -p. The ball that bounces off transfers more momentum to the wall that the one that sticks.

The used to sell light pinwheels in novelty shops [still do, i suppose]. The 'clockwise' face of each vane is painted white, the opposing face is painted black. It is suspended in an evacuated glass container to eliminate air resistance. When exposed to bright light, the wheel spins clockwise.

 

[BobG]

The used to sell light pinwheels in novelty shops [still do, i suppose]. The 'clockwise' face of each vane is painted white, the opposing face is painted black. It is suspended in an evacuated glass container to eliminate air resistance. When exposed to bright light, the wheel spins clockwise.

These pinwheels actually work on heat differential, not solar pressure. It's virtually impossible (at least with today's technology) to test the effects of solar pressure on Earth. To come close, the evacuated glass container would have to be a perfect vacuum, vs. the extremely low pressure it actually is.

I'm not alone in trying to figure out how to correlate solar pressure with the idea that light will leave a 'perfect' mirror with the same energy it entered.

Thomas Gold (Center for Radiophysics and Space Research, Cornell University) has some doubts, as well.
http://www.arxiv.org/html/physics/0306050

I have some problems with his paper, though. The biggest is that satellites reportedly do experience a force from solar pressure. Solar pressure can cause torques which disturb satellite attitude and changes the eccentricity of geosynchronous satellites, given enough time.

Louis Friedman, working on the Cosmos I, a satellite which will use solar sail propulsion defends the idea that solar pressure does exert a force on satellites:
http://www.planetary.org/solarsail/ss_and_physics.html

I have some doubts about how well the experiment will work so close to Earth and even they realize the observed effects are likely to be very small. (Other effects, such as gravity gradients, tend to dwarf the effect of solar pressure for low orbiting satellites.

If solar pressure does exert a net force on a satellite, then there has to be energy conservation. The light has to lose some energy in transition. This letter comes closest to explaining how energy balances out:
http://solarsails.info/news/newscientistletter.html

Since the energy of light depends on its intensity and frequency, the light reflected off the mirror has to see a reduction in one or the other.

 

[BobG]

Take a speed and reverse it, you get -v. Since the energy equation includes v^2, the minus signs cancel out and you get the exact same energy as you had before, but in the opposite direction.

Momentum, on the other hand, has just v...

If you reduce v, don't you also reduce v^2?

 

[zoobyshoe]

The used to sell light pinwheels in novelty shops [still do, i suppose]. The 'clockwise' face of each vane is painted white, the opposing face is painted black. It is suspended in an evacuated glass container to eliminate air resistance. When exposed to bright light, the wheel spins clockwise.

That's a Crookes' Radiometer. It doesn't rotate because of the light hitting the vanes, though. It is chronically sold with that misinformation in accompanying literature. This site explains how it actually works:

Crookes radiometer
Address:http://www.fact-index.com/c/cr/crookes_radiometer.html

 

[Doc Al]

That's a Crookes' Radiometer. It doesn't rotate because of the light hitting the vanes, though. It is chronically sold with that misinformation in accompanying literature.

Right! If light pressure were the cause of the vanes spinning, the vanes would spin in the opposite direction than they do.

 

[russ_watters]

If you reduce v, don't you also reduce v^2?

Well sure - but who said anythign about reducing v? All you are changing is the sign. The magnitude stays the same.

 

[BobG]

Well sure - but who said anythign about reducing v? All you are changing is the sign. The magnitude stays the same.

I guess I just missed what you were trying to say.

I agree that reflected light has to leave at the same speed it entered. But something has to change in order to account for motion caused by solar pressure. If a more reflective surface results in a greater force exerted on the surface, then it would seem that the only thing that can change is the light's frequency. If solar pressure were causing the object to move away from the light source, then the frequency would change by default (Doppler effect).

This almost has to be the answer to what I was asking (how do you account for the motion of the object), but was asking for confirmation that this was what 'balanced' the equation.

 

[omin]

Two gods have bats made made of pure mirrorium. The pitcher throws photons at constant c, but each gods swings their bats at different speeds.

The photon enters the mirror with a speed based upon the perspective of it's last source, but this same photon does not leave the mirror it entered. You're all saying another photon leaves. This photon is manifested in the new reflection source and leaves at a rate based upon where it manifested. It follows Newtons laws launching forth from it's new source, forgeting it's previous launch conditions.

It sounds correct to say light's speed is constant, but it's constant from a source which means lights speed is determined by a combination of the source where it's manifested and the properties of light itself.

If a light is reflected, the source where reflection occurs can increase the lights velocity to a orginating source faster than light left the source originally, just by the newly reflecting source simply accelerating during the reflection process in the direction toward the previous source.

Correct or incorrect?

 

[BobG]

Two gods have bats made made of pure mirrorium. The pitcher throws photons at constant c, but each gods swings their bats at different speeds.

The photon enters the mirror with a speed based upon the perspective of it's last source, but this same photon does not leave the mirror it entered. You're all saying another photon leaves. This photon is manifested in the new reflection source and leaves at a rate based upon where it manifested. It follows Newtons laws launching forth from it's new source, forgeting it's previous launch conditions.

It sounds correct to say light's speed is constant, but it's constant from a source which means lights speed is determined by a combination of the source where it's manifested and the properties of light itself.

If a light is reflected, the source where reflection occurs can increase the lights velocity to a orginating source faster than light left the source originally, just by the newly reflecting source simply accelerating during the reflection process in the direction toward the previous source.

Correct or incorrect?

Incorrect. Each photon leaves the bat at the speed of light. Since the bat is moving the same direction as the photon, each photon is closer together. In other words, the frequency increases, not the speed.

Edit: Wow! This was the original question. The discussion became so sidetracked I almost forgot there was an original question.

The bat receives photons at a certain rate. It emits the photons at the same rate it received them. But, since the bat is moving, the photons are emitted closer together. That means another observer receiving the photons from the bat will receive them at a higher rate than the bat actually emitted them.

 

[omin]

The bat receives photons at a certain rate. It emits the photons at the same rate it received them. But, since the bat is moving, the photons are emitted closer together. That means another observer receiving the photons from the bat will receive them at a higher rate than the bat actually emitted them.

The pitcher now has to simultaneously pitch to two gods. Both gods step up to bat. The gods are exactly 60 feet from the pitcher. The pitcher winds up, then throws two photons. Both photons travel c toward both gods. One god is slightly distracted for a moment, but begins his swing just after the other god. The late swinging god compensates by accelerating his bat and in doing so hits the photon harder with his bat. One more thing, both bats hit their photons at the same time.

Do the photons absorb into each bat at the same rate? Does the new photon manifestation process occur at the same rate in each bat? Does each photon emerge from the bat at the same speed, relative to the playing field?

If photon absorbtion and manifestation is simultaneous, and emergece of photons from the bat have the same speed, where does the extra energy go that the late swing god exerted in his swing?

Speed c is determined by the source or what?

If the photon is unaffected by the instataneous intertia of the bat during it's emergence from the bat, then its speed c of emergence is relative to what?

If the photon is affected by the instantaneous inertia of the bat (it's physical origin now), then it should move speed c from the instantaneous inertia of the bat, right?

If the later is true, then late swinging god's photon is now moving faster than the other photon.

 

[BobG]

Since the late swinging god's bat is moving faster, they could only hit one photon each at the exact same time. Both would receive the photon at the speed of light - both would send the photon skyward at the same rate.

However, light consists of many photons. It has a wavelength (in fact, that's what distinguishes color). The late swinging, fast swinging god will receive photons at a faster rate than the early swining, slow swinging god. Both will emit photons at the same rate they were received (each photon emitted at the speed of light). Each bat moves between emission of a photon, so even though the photons are emitted at the same rate (frequency) and speed they were received, the photons are emitted closer together.

Players in the field will receive the fast swinging gods photons at a faster rate (frequency) than the slow swinging god, since there was less distance between the photons emitted by the fast swinging gods. Each photon is traveling at the speed of light.

Energy depends upon how many photons each batter is emitting at a time (intensity) and the rate they are emitting the photon packets (frequency). So the difference in energy between the fast swinging god and the slow swinging god is reflected by the rate the players are receiving the photons.

In other words, the energy of the swing is reflected by how many photons are received over a given amount of time, not the speed of each photon.

 

[terrabyte]

if it's just one photon, energy of the swing makes no difference.

photons have no mass to be accelerated in this fashion

 

[omin]

Since the late swinging god's bat is moving faster, they could only hit one photon each at the exact same time. Both would receive the photon at the speed of light - both would send the photon skyward at the same rate.

Hey Bob, you answered, thank you, but could you explain, because it's not common wisdom to those trying to understand, which is often the only effect of pat answers. This is the question you answered:

Does each photon emerge from the bat at the same speed, relative to the playing field?

An explanation I'm sure would answers these questions:

Do the photons absorb into each bat at the same rate? Does the new photon manifestation process occur at the same rate in each bat?

If photon absorbtion and manifestation is simultaneous, and emergece of photons from the bat have the same speed, where does the extra energy go that the late swing god exerted in his swing?

Speed c is determined by the source or what?

If the photon is unaffected by the instataneous intertia of the bat during it's emergence from the bat, then its speed c of emergence is relative to what?

If the photon is affected by the instantaneous inertia of the bat (it's physical origin now), then it should move speed c from the instantaneous inertia of the bat, right?

 

[omin]

if it's just one photon, energy of the swing makes no difference.

photons have no mass to be accelerated in this fashion

All things with physical properties can have action and reaction. (Newton Law III)

Photons do have action and reaction because the full process involved in human vision consciousness directly reacts to photons, which means humans sense photons.(Empiricism)

Only things with physical properties can be sensed, which is only directly by humans or human aided sense, instruments. All things with physical properties have the property of mass. (Empiricism, Technology, The Physical Property of Mass and NL III)

Therefore, photons have the property mass.

If photons don't have mass, then should I throw out Newtons Laws? Newtons laws seem to me to imply mass to anything sensed. Or what?

 

[russ_watters]

If photons don't have mass, then should I throw out Newtons Laws? Newtons laws seem to me to imply mass to anything sensed. Or what?

Newton's laws have well known limitations and that's one of them.

Only things with physical properties can be sensed, which is only directly by humans or human aided sense, instruments. All things with physical properties have the property of mass. (Empiricism, Technology, The Physical Property of Mass and NL III)

Since when? That's an assumption based on a narrow-minded view.

All waves, by definition, have no mass.

omin, you asked a lot of questions about C in previous posts. Have you read what Special Relativity has to say about it? It's the second postulate you should be concerned with.

 

[omin]

Newton's laws have well known limitations and that's one of them. Since when? That's an assumption based on a narrow-minded view.

All waves, by definition, have no mass.

omin, you asked a lot of questions about C in previous posts. Have you read what Special Relativity has to say about it? It's the second postulate you should be concerned with.

Waves are psychologial theories, which are physically subjective as we speak. I insist they only become thoughts (theory in the mind), because they have a physically properties of a objective origin, unless wave theory has nothing to do with the physical world and is pure fantasy of the imaginative human subjective realm. Any valid theory derives from physics. Is wave theory valid, then? If so, are you saying wave theory is a figment of the mind only and represents only subjective fantastic order? If not, I momentarily put words in your mouth. I apologize on that point. The book Wu Li Masters claims physically objective originating cause of the subjective wave theory through descriptions of past experiments.

I've read the second postulate, but the explanations in my text and in the video I watched represent things in a way that is outside my understanding. That is why I am questioning for explanation. I could give you the pat answers the texts and video asserted, but that doesn't mean I understand. Understanding it is what I am after, not memorization.

Furthermore, narrow minded? I'm open for explanations, how is that narrow minded. I never asserted anything that asserts I am right and everything beyond that is wrong.

Come on man.