Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 16/11/2007 23:45:32
-
Dear Luke...Darth and other Light Saber Wiedlers,
See this light ?
[ Invalid Attachment ]
Nice isn't it ?..Notice how busy it is moving fast and being non-dark ?
But...if something moves really fast it gets really hot yes ?.....friction eh ?....so why doesn't light from my torch feel really hot and why doesn't it make the air explode as it moves through it very fast.....?
Enlighten me will ya !!
hugs and shmishes
Neil
xxxx
-
Heat comes not from speed, but from energy. Speed contributes to energy, but so does mass (and light has no rest mass, and the overall kinetic energy of light is small compared to the kinetic energy of most baryonic matter even at moderate speeds). The other issue is how much of this energy is given up to its environment (friction means that the object is constantly losing energy to its environment, and this is caused by the surface interaction of object and its environment). In a purely transparent environment, light will not lose any energy to its environment; although in practice, most real world environments are not totally transparent, so light will lose some of its energy to its environment, and so will impart some heat to its environment, but it may be only a very small amount of its energy, depending on how transparent the environment is).
Certainly, a very intense laser beam projected at a surface that will absorb the light, and so absorb the energy from the light, can cause massive local heating, and a small explosion.
The situation with ordinary everyday objects is that they will interact with the surrounding air through the electric fields generated by the electrons on the surface of the atoms. This electrical interaction allows a transfer of energy between the atoms, without actually stopping the atoms.
Since light (the photon) is electrically neutral, so it cannot have this kind of interaction, although it can impart energy to an electron if it actually collides with it.
-
The other effect is that air is just very very very transparent, so even if you have a light beam that would be powerful enough to make air heat up and essentially explode if it were absorbed, because the air is so transparent the energy isn't absorbed and carries straight on.