Unraveling the Physics of Frost on a Car Sunroof

In summary: So the frost lines on the car would be more likely to form on the lower, more energy-rich areas of the scratch.
  • #1
DaveC426913
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What is the physics behind this kind of frost, seen on the sunroof on my car?

Why does it form so linearly, even though every line has feathery offhsoots? (Why don't they all form radially, more like snowflakes?)

Why are lines able to cross each other with apparently no interaction?

I could see if these lines were being formed from pre-existing scratches in the windshield - that would explain both the above questions, since it would mean the structure of the lines has much more to do with the surfacfe and much less to do with the formation of crystals. But wouldn't the scratches have a more regular pattern, such as in line with the car's motion?
 

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  • #2
DaveC426913 said:
What is the physics behind this kind of frost, seen on the sunroof on my car?

Why does it form so linearly, even though every line has feathery offhsoots? (Why don't they all form radially, more like snowflakes?)

Why are lines able to cross each other with apparently no interaction?

I could see if these lines were being formed from pre-existing scratches in the windshield - that would explain both the above questions, since it would mean the structure of the lines has much more to do with the surfacfe and much less to do with the formation of crystals. But wouldn't the scratches have a more regular pattern, such as in line with the car's motion?

It would depend on scratches only, if the windscreen were perfectly clean; the process of crystals nucleation is complex, it could also be due to the presence of microscopic dust particles or glass imperfections but also on pre-existing (before using the car) microscopic scratches.
 
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  • #3
Dedritic crystals (like snowflakes) form when the energy balance between new surface area and phase change is negative, IIRC. That is, when it's energetically favorable to create new surface area (because the interfacial energy is low), a nucleating crystal will form a dendritic hanbit. There was a good experiment called "Isothermal Dendritic Growth Experiment (IDGE)" done on the space shuttle. A good discussion of the physics is here:

http://www.rpi.edu/locker/56/000756/

Now, on a scratched surface, the surface energy will be lower in some places than others (due to the scratch), and so a crystal will preferentially follow the groove.
 
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Related to Unraveling the Physics of Frost on a Car Sunroof

1. What causes frost to form on a car sunroof?

Frost forms on a car sunroof when the temperature of the glass surface drops below freezing. This causes the moisture in the air to freeze onto the surface, creating the frost.

2. How does the angle of the sunroof affect frost formation?

The angle of the sunroof can affect frost formation because it can change the amount of sunlight that reaches the glass surface. If the angle is tilted towards the sun, it can warm up the glass and prevent frost from forming. However, if the angle is flat or tilted away from the sun, it can allow for more heat loss and increase the likelihood of frost formation.

3. Can the material of the sunroof impact frost formation?

Yes, the material of the sunroof can impact frost formation. Different materials have different thermal properties, meaning they can retain or release heat at different rates. This can affect the temperature of the surface and how quickly frost forms.

4. Can wind affect frost formation on a car sunroof?

Wind can indirectly affect frost formation on a car sunroof. When there is wind, the air around the car is constantly moving and mixing, which can prevent the formation of frost. However, if the wind is strong enough, it can also decrease the temperature of the glass surface and increase the likelihood of frost formation.

5. How can I prevent frost from forming on my car sunroof?

To prevent frost from forming on your car sunroof, you can park your car in a garage or cover it with a tarp. This will help to keep the temperature of the glass surface above freezing. Additionally, you can try using a de-icer spray or rubbing alcohol to melt any existing frost on the sunroof. Keeping your car's interior warm can also help to prevent frost formation on the sunroof.

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