Quick Science question

[ma junior]

I have a question and i have searched all over for the answer but couldnt find it so i come here,

the question is if you attach a big flashlight or lightbulb to the back of a wagon and turn it on so the light is shining one way, would the wagon accelerate in the opposite direction at the speed of light? please this question is really bugging me and i need an answer, and possibly an explanation

[Phier]

Why are you getting all your questions from 4chans 'troll physics'?

They are put there because they are silly and not true.

[Eikki]

you seriously dont know the answer to this question ? http://knowyourmeme.com/memes/troll-...-troll-physics

[ma junior]

you seriously dont know the answer to this question ? http://knowyourmeme.com/memes/troll-...-troll-physics

hey yeah thats the picture i saw! but i didnt get it from there i got it from some other site

[ma junior]

no i didnt get it from 4chan i saw it on a website when i typed in how to travel at speed of light in google and thought about it made me think though, why doesnt it happen?if a rocket fires back at 100 mph then it would go in the opposite direction at 100 mph so why not light,

[Juvenal]

...if you attach a big flashlight or lightbulb to the back of a wagon and turn it on so the light is shining one way, would the wagon accelerate in the opposite direction at the speed of light? please this question is really bugging me and i need an answer, and possibly an explanation

If you stood on the back platform of a train and kicked a football down the track, would you really expect the train to move forwards at the same speed as the football went back?

[Eikki]

Its impossible because F = ma, where F = force, m = mass and a =accl'n
so , a= F/m : m is the mass of the wagon. the Force exerted by light affects tiny particles but is nowhere near enough to cause acceleration. the F/m in such a case is negligible, so no acceleration

[ma junior]

Its impossible because F = ma, where F = force, m = mass and a =accl'n
so , a= F/m : m is the mass of the wagon. the Force exerted by light affects tiny particles but is nowhere near enough to cause acceleration. the F/m in such a case is negligible, so no acceleration

what if its in space?

[Eikki]

the mass never changes, only weight due to the effect of gravity. It is still too much as a denominator compared to the force numerator for there to be any noticeable acceleration.

[Gordon Freynman]

There is no force exerted by photons when they are emitted from a light source, hence there would be no reaction force, so no there wouldn't be any acceleration.

[Juvenal]

There is no force exerted by photons when they are emitted from a light source, hence there would be no reaction force, so no there wouldn't be any acceleration.

Not quite (I think... see EDIT at bottom of post).

I'll quote Wikipedia since this isn't particularly controversial.

There are two sources of solar forces. The first is radiation pressure, and the second is due to solar wind. The radiation pressure is much stronger than the wind pressure. In 1924, the Russian space engineer Friedrich Zander proposed that, since light provides a small amount of thrust, this effect could be used as a form of space propulsion requiring no fuel. Einstein proposed and experiments confirm that photons have a momentum p=E/c,[2][3] hence each light photon absorbed by or reflecting from a surface exerts a small amount of radiation pressure. This results in forces of about 4.57x10−6 N/m2 for absorbing surfaces perpendicular to the radiation in earth orbit, and twice as much, if the radiation is reflected.[4] This was proven experimentally by Russian physicist Peter Lebedev in 1900.[5]

EDIT. OK, the above describes photon absorption/reflection not emission. I think it applies to emission as well otherwise we have a problem with conservation of momentum. Of course most light sources emit equally in all directions, hence no net force. But in the case described by the OP, the lamp does experience a small forward thrust due to light striking its reflector.

[Gordon Freynman]

EDIT. OK, the above describes photon absorption/reflection not emission. I think it applies to emission as well otherwise we have a problem with conservation of momentum. Of course most light sources emit equally in all directions, hence no net force. But in the case described by the OP, the lamp does experience a small forward thrust due to light striking its reflector.

I'm pretty sure it doesn't apply to emission, because photons are emitted by excited electrons which react by dropping to a lower energy level in an atom, and AFAIK that doesn't exert any force on the atom. I could be wrong though, quantum interactions can get very confusing in non mathematical terms.

[Juvenal]

I'm pretty sure it doesn't apply to emission, because photons are emitted by excited electrons which react by dropping to a lower energy level in an atom, and AFAIK that doesn't exert any force on the atom. I could be wrong though, quantum interactions can get very confusing in non mathematical terms.

Yes, upon further reflection I realise you must be right, otherwise any atom that emitted a photon would immediately take off in the opposite direction!

However, as I said before, the OP's wagon would indeed feel a forward force, generated when photons from its lightbulb strike the wagon (or even the lamp's reflector if it has one). Of course it wouldn't be enough to overcome friction.

[Banana Jelly]

Wow a serious discussion from a troll thread?

And no, it wouldn't...

[Tacitursa]

if a rocket fires back at 100 mph then it would go in the opposite direction at 100 mph so why not light,

[Eikki]

Isaac Newton is facepalming in his grave. Third Law fail OP.
And I see this isnt the first time you have posted about 'troll physics' as it is called on 4chan
http://www.twcenter.net/forums/showt...64#post8341264

[ma junior]

OK, FINE if you think im for any reason am doing what you people call "trolling" then delete this thread,

i do not want to be banned or discreditied or anything for posting a simple question which will be interpreted by you people as trolling. thats just how it is, any new person to science and thinking comes and asks a simple or odd question, he will get piled by the more scientific minded people and treated as a troll. yes i got the question from looking at another website which had images like this but that particular one made me think, which is why i came to this forum to see what you, as a scientifiic community would make of that question and the other theories in the other thread and possibly seek a scientific answer, i wasnt intending on trolling you people and if you feel that way then dont post here seems i have to go elsewhere to ask questions

so forget it dont answer and how do you delete threads?

[Gordon Freynman]

OK, FINE if you think im for any reason am doing what you people call "trolling" then delete this thread,

i do not want to be banned or discreditied or anything for posting a simple question which will be interpreted by you people as trolling. thats just how it is, any new person to science and thinking comes and asks a simple or odd question, he will get piled by the more scientific minded people and treated as a troll. yes i got the question from looking at another website which had images like this but that particular one made me think, which is why i came to this forum to see what you, as a scientifiic community would make of that question and the other theories in the other thread and possibly seek a scientific answer, i wasnt intending on trolling you people and if you feel that way then dont post here seems i have to go elsewhere to ask questions

so forget it dont answer and how do you delete threads?

Just ignore them, or if you're feeling evil you could report the post as being disruptive. The rest of us however gave you definitive answers.

Send a PM to one of the local moderators and they'll either lock or delete the thread.

I see you've used my own link from post #11.

Right... >_>

[Elfdude]

Light has mass and emission of photons causes acceleration. Directing this acceleration is difficult without using a reflector, but in theory were you to emit a beam of photons it would cause acceleration. A flashlight would cause acceleration in space because its reflectors (which direct the beam of light forward) act as solar sails (although very tiny and very ineffectual ones) catching the photons and creating directional force. If you want to test whether photons have mass put a piece of tin foil in front of a strobe light, you can hear the impacts of the photons. So, it seems most people in this thread aren't entirely correct.

However this acceleration is equal to the mass of the photons which is obscenely tiny, it dubious that if you took a satellite with a typical flash light into a hypothetical space devoid of other variables that you'd notice the object moving or accelerating at all given that the rate of it's acceleration is equal to the force being added to it's vector (which is equal to the mass of the photons).

[Plant]

Light has mass and emission of photons causes acceleration. Directing this acceleration is difficult without using a reflector, but in theory were you to emit a beam of photons it would cause acceleration. A flashlight would cause acceleration in space because its reflectors (which direct the beam of light forward) act as solar sails (although very tiny and very ineffectual ones) catching the photons and creating directional force. If you want to test whether photons have mass put a piece of tin foil in front of a strobe light, you can hear the impacts of the photons. So, it seems most people in this thread aren't entirely correct.

However this acceleration is equal to the mass of the photons which is obscenely tiny, it dubious that if you took a satellite with a typical flash light into a hypothetical space devoid of other variables that you'd notice the object moving or accelerating at all given that the rate of it's acceleration is equal to the force being added to it's vector (which is equal to the mass of the photons).

Wrong, light does not have mass.

If you want to test whether photons have mass put a piece of tin foil in front of a strobe light, you can hear the impacts of the photons. So, it seems most people in this thread aren't entirely correct. So, it seems most people in this thread aren't entirely correct.

I sincerely hope you aren't serious.

Most people in this thread aren't correct, but it's not because light has mass.