Why does the road surface appear to shimmer when itís hot?
When air is hot it expands and light will go through hot air slightly faster than cold air. When light changes its speed at an angle it will bend like when it goes into glass or something. You get lots of turbulence with air moving up which light will go through faster. So you get light bending in all sorts of directions which change as the air moves and you get this turbulence effect.
Fran asked the Naked Scientists: Sometimes on a hot summer day you can see "heat" radiating from really hot surfaces it sort of shimmers. Since you can't see air move, what exactly are we seeing? thanks and I love your show What do you think? Fran, Sun, 1st Jun 2008
The surface is hotter than the air. This means the air heats up & consequently rises (air - the same as all gases - expands as it is heated, causing the pressure to drop to a level lower than the air above it & that makes it rise). The rising air plays havoc with lightwaves & the shimmering you see is due to lightwaves being distorted.
Show off! DoctorBeaver, Sun, 1st Jun 2008
OI... I'm the pedant around here! DoctorBeaver, Sun, 1st Jun 2008
It really does look as though I am gunning for you at the mo.