system
Given the following post, respond as if you're commenting on Reddit:
human
Why are some forms of EM transmission line-of-sight and others are not?

I was trying to explain to a customer that their TV remote used infrared and needed to be pointed directly at the receiver while their PS3 remote used bluetooth and did not require line of sight when it occurred to me that both IR and radio waves are different forms of the same phenomenon.  Visible light and IR (UV as well, I assume) both require line-of-sight to transmit their "data."  You can bounce it off reflective material, but it will not penetrate most forms of matter (or if it does, not very well).  

Radio waves, on the other hand, don't really care.  Sure, your cell phone might lose a few bars when you go inside a cement building and I know there are some places that do a very good job of blocking out radio signal but my PS3 remote will still function from the toilet (don't ask.)

At first I thought maybe it was because radio waves were smaller and could pass through the matter, but they're actually very large compared to light/IR waves.

What up wit dat?


Edit:  In the title, by "transmission" I did indeed mean "radiation."
gpt
Your first instinct about absorption is on the track.  IR waves are absorbed by most matter, while radio waves are not.

This is due to how EM waves are absorbed by atoms.  If an EM wave "hits" an atom, there are a couple of things that can happen:

1) The EM wave can be absorbed, and the excess energy can be dissipated by vibration.  This is how the sun heats materials.

2)The EM wave can be absorbed and then re-emitted. The color of a material is dependent on what wavelengths are re-emitted.

3) The EM wave can pass past the atom without being absorbed, with the path maybe changed due to the polarizability of the atom. This is what usually happens to radio waves.

Which of the three options happens is determined by the energy level structure of the material hit by the radio waves.  In order to be absorbed, the energy of the incoming EM wave must be close to the gap between two of the energy levels of the material.

Radio waves have a long wavelength, and thus have low energy.  The band gaps of most materials are larger than the energy of a radio wave, meaning that only a small number of photons from the radio wave is absorbed.  This is why the drywall in your house will not stop the radio wave, but a foot or more of concrete probably would.