MadSci Network: Other

Re: How do I post a follow up question to a recently answered question?

Date: Sun Jun 10 16:54:26 2001
Posted By: Matthew Buynoski, Senior Member Technical Staff,Advanced Micro Devices
Area of science: Other
ID: 989958274.Ot

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 

  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 

   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 

   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 

   Mad Scientist:  Photons don't accelerate. They are always moving at light

   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 

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