MadSci Network: Physics

Re: how does light travel... especially in a vacuum (like space...which apparently isnt a true vacuum)

Date: Fri Jun 15 03:13:33 2007
Posted By: Gene L. Ewald, Secondary School Teacher, Retired, Amer. Assoc. of Physics Teachers
Area of science: Physics
ID: 1181669336.Ph

Dear viagnehy,

Let me first comment on your statements; then I'll try to answer your question.

� sound waves have to vibrate on something to exist, ... We refer to sound as any vibration that causes a response to our ears. They may come through air , water, or a solid object in contact with our body. Depending on the medium outside our bodies, those waves may be transverse, longitudinal or torsional. Once in our bodies, they travel in a variety of modes to our brains where they are regarded as some type of recognizable signal or just "noise". Clearly our auditory system responds to a physical frequency where "something" actually moves.

� we move by walking on hard surfaces, The surfaces we walk on can't seem to figure out what to do with us. To stay on the surface, the "top surface", upon which we walk, must repel our outer surface by a force referred to as a Normal Force. "Normal" , in this case, means perpendicular rather than common/ordinary. The force is normal to its own surface and is pushing us away. At the same time, there is an attraction of sorts in the form of friction ... a kind of sticky force that doesn't let us slide by. So we are rejected in a normal direction and attracted in the parallel direction.

� birds fly by manipulating air Air, due to its large gaps between particles, doesn't provide nearly as much normal force as do most solids. However, birds ( large wing area to weight ratio) seem to get by pretty well. Of course they must work at it and can't rest for long periods like we do on the couch.

? does light "move" ?? So far I have been writing about "objects" and their interactions with other "objects". The term refers to things that generally have mass and occupy space. "Objects" make it difficult for other "objects" to move their masses into currently occupied space. Just as real are things that generally don't have measurable mass and do not occupy space at the exclusion of others. Fields are among such things. The regions of influence caused by charge, mass or magnets don't exclude other fields ... nor do they require mass in that region to exist.

A vibrating bell may not be heard from inside a vacuum, but a vibrating magnet can cause a compass needle to vibrate. The process of electromagnetic induction is a two-way street. A changing magnetic field can cause a flux in an electric field. A changing electric field can cause a flux in a magnetic field. This apparent cycle doesn't happen instantaneously everywhere. So there is a finite amount of time for a response to take place ... hense the "speed" of the wave.

Light is any frequency of these E-M inductions. Visible light is a very narrow band of the spectrum that our body can sense. Other parts of our body react to infrared or ultra-violet. Radar frequencies were known to warm technicians' hands during WWII. The first microwave marketed after the was was called the "Radar Range". Water resonates at those frequencies. Anything with water or similar molecules can be heated by 2-5 cm wavelengths of light. That includes meat from any animal (us included), fresh vegetables, cold coffee, of course, but not dry materials like a paper plate.

In general, light moves the fastest in a vacuum. Passing through air, water, glass, or other "transparent" materials will slow the process. It can be thought of as having obstructions in the way much like we can drive/walk faster when our path is not filled with other things.

Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2006. All rights reserved.