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shogun7
09-11-2004, 03:58 AM
On a cold, rainy day, ice forms more quickly on bridges and overpasses for two reasons: WHY? :rolleyes:

Charnwood
09-11-2004, 05:32 PM
Greater surface area?

RIZZLA
09-11-2004, 06:18 PM
Lower temps from above and below

riz

Abe
09-11-2004, 10:55 PM
Zzzzzzzzzzzzzzzzzzzzzz

shogun7
10-11-2004, 03:36 AM
Zzzzzzzzzzzzzzzzzzzzzz

Yup just as I thought there’s always a schlock who falls asleep.
I think if you look at the definition of literacy, you can figure out how to answer the question.
Webster states literacy is the ability to read and write. Simply knowing this, you should be able to tackle this question. Teaching literacy is the basis of and the most basic thing we do as educators. It's certainly cross-curriculum and a way to keep your brain active...maybe :D

Dan
10-11-2004, 04:07 AM
On a cold, rainy day, ice forms more quickly on bridges and overpasses for two reasons: WHY? :rolleyes:

If you never brought up the question, I would rely on the questions I had wondered about. The signs that say "Bridges may be slippery when wet."

I satisfied myself with the answer that has been alluded to in different words by others in this thread:

The temperature beneath the bridge is affected by the temperature of the air. The road leading up to the bridge has an underside unaffected by the change in air temperature.

The bridge would also thaw out more quickly than the road leading up to it, when the transition of temperature reverses, for the same reasons.

The two reasons you ask for elude me. I will hazard my answer:



The surface of the bridge will become colder more quickly than the surface of the road because both sides are exposed to heat transfer by convection.
It is a rainy day, thus a lowering of temperature could create an icy condition.


It's not quite necessarily a zzzzzzzzzzzz question.

My answer has ignored an evaporative and latent effect, for example. :)

shogun7
10-11-2004, 04:36 AM
Dan, All are correct except ZZZZZZZZZZZZZ. I get the feeling that some people think I tying t show off but nothing could be further from the truth I'm to old for that nonsense and besides I am my severest critic. I liked the question because I never thought much about it :) The answers are:

· 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. A similar question is. "Why does one's tongue stick on a cold pipe"? and what kind of sensation is felt when it's removed? :rolleyes:

Brian_UK
10-11-2004, 12:35 PM
A similar question is. "Why does one's tongue stick on a cold pipe"? and what kind of sensation is felt when it's removed? :rolleyes:
First answer:- Why stick your tongue on a cold pipe ?

Second answer:- Ouch, you prat (said under your breath or out loud if required. :cool: