Toughened Ice

[cpvh]

Why is it that the ice that forms on the windscreen is much harder to shift than that which forms on the other windows of the car?

[NOSPAMnet]

Yeah.That's true.It is very hard isn't it . You've not had any yet have you?

[Bob Mannix]

Being less vertical, there is less run off of condesing water prior to freezing, so the windscreen ice tends to be thicker. Often, sometimes, the windscreen is facing away from the buildings and is more exposed as well. Well, I just made all that up but it sounds plausible!

[Dave Plowman (News)]

Probably because it's cleaner so the ice gets a better hold. The traffic film on the others only gets partially removed by washing.

Also the further from vertical the window is the more the ice seems to form.

[mike]

You used to be indecisive but now you're not so sure?

[Bob Mannix]

-You used to be indecisive but now you're not so sure?

ooo that's a tricky one....I think so :o)

[Stephen Howard]

Interesting question....often noticed it but never really thought about why it should be.

I doubt it's that the glass is any colder than the rest, so I'm going to go for the glass being cleaner, thus allowing the ice to bind more effectively to the surface. You should notice a difference in the amount of elbow grease it takes to shift the ice from the area outside the sweep of the wipers compared to that within it.

Regards,

[Stephen Howard]

Not sure that's entirely true, as I've noticed that it's as easy to clear ice of the sunroof as it is the side windows. However, your theory might fit in with that of mine ( the glass being cleaner ) inasmuch as condensing water isn't dispersed by dirt and thus tends to form beads, which will undoubtedly be harder to remove than the relatively flat layer of ice on the other glass. The aspect makes a difference - on mornings where there's a light frost the glass in the lee of the wind is often quite free of ice.

Regards,

[The Natural Philosopher]

upward slanting surface gets colder.

[marpate1]

I had to scrape the wife's car today :( seems too early to me, but we had no clouds last night and live on top of a hill so wind chill may have played a part I guess.

[Stephen Howard]

Yet it's easier to remove the ice from the rear of an estate and a hatchback...the former having a steeper angle than the windscreen, the latter more less so.

Regards,

[BigGirlsBlouse]

I have a quick clear electrically heated windscreen...the days of doing all that scraping are well and truely over :)

[ARWadsworth]

I had to scrape the wife's car today :( seems too early to me, but we had no clouds last night and live on top of a hill so wind chill may have played a part I guess.

You are under the thumb. Tell her to scrape her own screen.

The first ice on a windsceen = bonfire night. I can see a massive party happening near the 5th of November at my house.

Adam

[Weatherlawyer]

Always assuming there is truth in the question, the fact that the screen would be cleaner, better polished and in the streamline would all tend to make the windscreen a more difficult surface to form on rather than the easier one presumed by most of your correspondents.

However, once crystals form they will be easier to grow and harder to remove.

I just give the screen a squirt of de-icer from a made up solution (spray on ether based crap just wastes time and patience.) One of those kitchen cleaner spray bottles is ideal.

Hit the bonnet too as that is a source of cold air and moisture.

It's cheap, effective and quick.

What is most annoying is that the stuff is always at its greatest cold and thickness on the days I am late for work. The timing is excellent.

If I was going to work at 4 am, it would be nothing more than dew with potential to annoy. If I was going off at 10 am it would be melting.

How does it know that that 6:30 to 8:00 am is the sweet spot? Barrsud!

[ARWadsworth]

Proper toughened ice.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "ARWadsworth" saying something like:

altogether.

[Weatherlawyer]

ice roads for heavy traffic.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Weatherlawyer saying something like:

Impractical in term of cost for all but the shortest of roads.

[Yokel]

|> Why is it that the ice on the windscreen is harder to |> shift than that which forms on the other windows of the car? | |Always assuming there is truth in the question, the fact that the |screen would be cleaner, better polished and in the streamline would |all tend to make the windscreen a more difficult surface to form on |rather than the easier one presumed by most of your correspondents.

Have a look at the shape of your car. In particular, note the *slope* of the pieces of glass in the windows.

Modern aerodynamic styling favours a shallow angle windscreen to ease the airflow with a rather steeper back window. To provide the maximum space for passengers, the side windows are almost vertical.

What has this got to do with it? On a clear night, surfaces cool below air temperature by radiation to outer space. Vertical windows have a low exposure to the sky and so will not cool below air temperature so much. If your car is parked near the house (as mine is), the heat from the house may well outbalance the radiation loss to such sky as the windows on that side see and so they will not freeze at all.

The more sloping front and back windows will lose more heat to the sky and so cool further below air temperature. It is this that encourages the thicker and harder ice layer to form. Because ice is a very good radiator at infra-red wavelengths, once that ice layer starts to form a "feedback" sets in to magnify the effect.

It also depends on the dew point. If the dew point is below freezing, hoar frost will form directly on the glass. If it is just above, water will form first and then freeze. This last is much harder to remove than frost alone. Likewise, if it has been raining and the rainwater film freezes.

[tony sayer]

Sounds very odd to me if an object radiates that doesn't have to go up to the Sky at all..

When the clouds clear the infra red is lost to space when the clouds are there its reflected back!..

Sure this isn't anything to do with dew or water particles and the incline of the surface?..