2007-01-15 18:33:11 · 6 answers · asked by spak 1 in Science & Mathematics ➔ Earth Sciences & Geology
On a cold, rainy day, ice forms more quickly on bridges and overpasses for two reasons:
The freezing wind strikes the bridge above and below and on both sides, so it's losing heat from every side. The road is only losing heat from its surface. Even while the temperature on the road surface is dropping, the heat underneath the road keeps it warm enough to prevent icing as temperatures in the atmosphere drop below freezing. Bridges have no way to trap any heat, so they will continually lose heat and freeze shortly after temperatures in the atmosphere hit the freezing point.
Most bridges today are built with steel and concrete, both of which are good heat conductors. Because these materials conduct heat, any heat that the bridge has moves through the bridge to the surface where the heat is lost through the air flow around it. Roads are mostly made from asphalt, which is a poor conductor of heat, and that lessens the rate of heat loss from the road.
The bottom line is that a bridge will follow the air temperature very closely. If the air temperature falls below freezing, a bridge's surface will fall below freezing very quickly. Rain or snow, therefore, will freeze and stick to the bridge.http://science.howstuffworks.com/question566.htm
2007-01-15 18:41:31 · answer #1 · answered by Katrina 3 · 1⤊ 0⤋
yep...that's right. because the ground (what's under a road) is warmer than the air (what's under a bridge). So the cold air surrounds the entire bridge causing it to freeze before the ground as it takes a while for the ground to lose it's heat and become more cool.
2007-01-16 02:42:42 · answer #2 · answered by prekinpdx 7 · 0⤊ 0⤋
It has to do with the air currents. When cold air passes over and under the bridge it cools the bridge faster than the ground. When the ground is damp, the bridge can freeze before the ground does.
2007-01-16 02:38:27 · answer #3 · answered by GermanPickle 2 · 1⤊ 2⤋
They are not insulated underneath like a regular road is insulated underneath by soil. Therefore, their temperature of the bridge falls more rapidly and precipitation will freeze more rapidly on a bridge as opposed to a road.
2007-01-16 02:39:11 · answer #4 · answered by Some Guy 6 · 3⤊ 0⤋
I think it is b/c they cool the fastest, and what moisture was on the surface turns to ice, before any roads do. They cool faster b/c they are up high, and nothing to insulate them. Roads get some delay from freezing b/c the earth underneath may not be cool enough to freeze.
But this is just my theory...I was also wondering why.
2007-01-16 02:40:31 · answer #5 · answered by Sam M 4 · 1⤊ 0⤋
no time
i know the ANSS perfectly
2007-01-16 03:38:58 · answer #6 · answered by srinu710 4 · 0⤊ 1⤋