|MadSci Network: Other|
Hello, Philip! You've asked a number of questions, so let's go through them one at a time. Philip: "... "The only one of these things which is truly massless is heat, Light has a very small amount of mass according to the theory of relativity, albeit immeasureable, it is still implied." Is not light and heat (infered radiation) just different frequencies of the same kind of energy (EM vibrations)? Mad Scientist: Infrared radiation is indeed photons in a certain range of frequencies. However, what is usually referred to as sensible heat refers to the physical vibration (i.e. think of them as little hard spheres bouncing around) of atoms, electrons, or molecules. People tend to feel infrared radiation as warm, but that is only after it is absorbed and thus turned into vibrations. Philip: "How can heat be massless and light have mass? Additionally how can light (with some mass) travel at light speed? I have read numerous references that cite the massless nature of photons is what allows and even necessitates that light travel at light speed?" Mad Scientist: Photons have no REST mass. They do, however, have energy and that energy can be considered to be the same as a "relati- vistic mass" equal to that energy divided by the speed of light squared [E/(c**2)]. I have to differ somewhat from my colleague and say that there is a slight increase in mass due to vibrations as well. That is, the vibrating particles have non-zero velocities, and thus their relativistic mass is higher (by an ultra-tiny amount) than their rest mass (which is non-zero, and remains unchanged). Philip: "Perhaps the Mr. Duggan is referring to the mass of photons via acceleration?" Mad Scientist: Photons don't accelerate. They are always moving at light speed. Philip: "Perhaps he [Mr. Duggan] meant heat as the molecular motion of a system? If so then what is the difference between the definitions of heat (infered radiation) and the other (molecular motion of a system? Which concept is more valid? I'm very confused. Help." Mad Scientist: Molecular motion (e.g. my vibrations noted above) is one form of energy known as kinetic energy. Infrared radiation is photons, another form of energy. In this particular case, the infrared photons are pretty good at exciting molecular and atomic vibrations when they "hit" something. That is, the energy of the photon is transformed (by the absorbtion of the photon) into the kinetic energy of the moving molecule or atom or electron. This process also works in reverse. That is, the kinetic vibrations of matter causes photons to be emitted; for instance, red hot iron sends out a lot of infrared photons. Every object, emits some radiation, what frequencies and how much being mostly determined by its temperature, with the frequency distribution also being affected by what the body is made of. If this doesn't clear up your confusion, send in another question. When you do so, just refer to the message numbers (988153260.Ch and 989958274.Ph) as you did above. The moderators at the Mad Scientist Network can then route the question to either of us or to another Mad Scientist (if both of us happen to be on vacation or a business trip or whatever).
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