[rpm]

I was reading the thread on Tata Gravitas/Safari and there was quite some discussion going on about sunroof. Reading the different perspectives, the mention of safety hazards of a sunroof suddenly brings forth this old timer, tucked away neatly in some corner of my mind:

https://youtu.be/ve6XGKZxYxA

Naturally, a mish mash of sunroofs and the video above led me to the title of this article.

How will a glass roof affect the Faraday Cage, should the gods decide to test their mortal zapper, on the modern Faraday, in his glass cage? I think to myself, and it dawns upon me: I'm no Faraday.

I do what anyone named Not Faraday would: a quick Google search. Which.... doesn't yield any definitive results? Atleast none my brain and its 8 corners could decipher. So, with my less than stellar physics and more than rusty automotive knowledge, I turn to the ol' & trustworthy folks at TBHP to aid me in my quest for knowledge.



While at it, another question springs to my mind: How about.... An EV vs God's mortal zapper?

Oh, and my tomfoolery on google yielded another interesting topic: Sunroofs exploding. Yes, sunroofs that go ka-boom!

Article with data on failure rates across manufacturers here: https://www.consumerreports.org/car-...nger-overhead/

The preview of the juicy part (everyone loves graphs, right?)



Yet another question(/s). The last one, I promise
How often does this happen in India?
Has it happened to any BHPian?
Do they know anyone this happened to?



Mods please remove this thread if these questions have already been answered. I looked around and didn't find any matching threads. Please link them to me if you know.

[abhishek46]

I would like add one more question.

Can the sunroof (esp. the Panoramic ones) survive a hit from a small sized coconut?

[saikarthik]

Originally Posted by rpm

How will a glass roof affect the Faraday Cage, should the gods decide to test their mortal zapper, on the modern Faraday, in his glass cage? I think to myself, and it dawns upon me: I'm no Faraday.
Oh, and my tomfoolery on google yielded another interesting topic: Sunroofs exploding. Yes, sunroofs that go ka-boom!

Thank you for posting an interesting topic, and let the debate start for good.

This is the first time I am reading about a sunroof going ka-boom! I think these might be few probable cases in my opinion,
1. The difference in temperature - inside vs outside: But this would be the same case with the windshield.

2. Dynamic forces/stress acting on the glass due to road conditions and vehicle maneuvers: This might be the most probable cause considering monocoque construction and coupled effect of mechanisms (open/close).

3. Some defect on glass structure itself: this might lead to a crack or shattering, but not exploding.

Originally Posted by abhishek46

I would like add one more question.

Can the sunroof (esp. the Panoramic ones) survive a hit from a small sized coconut?

I guess it is the same case with the windshield.

[88_TANK_88]

With knowledge of physics limited to schooling and a couple of years in college, ( Public Advisory: I was not a very good student), the theory is that the lightning would take path of least resistance to the ground and thus travels through the metal portion of the car. The heat in such strikes is known to melt any plastic surrounding such conductors.

As far as glass is concerned, the most vulnerable would be rear windscreen with defogger wires through it. Tyres do often burst and occasionally catch fire.

[Sanidhya mukund]

I had never thought I would be opening my 12th grade books again, not in the least Physics. But your thread really tickled my brain.

This is what a book called S.L Arora has to say about this:


A figure from the 12th grade physics NCERT:


Going by the above, the body of a car is taken to be a hollow conducting sphere. And looking at the body of a conventional car, one would generally agree with this notion. However if you look at the Body in white (BIW) or the monocoque chassis, one would see that the body of a car is not actually a continuous metallic body.


The entire body, and most body panels are made of metal. But every car has windows and windshields. However, these do not cause any problems in case lighting strikes the car, because the body of the car is continuous around the glass pieces, I.e through the pillars that connect the roof to the rest of the metal body.

Hence by this logic, it should also not be a problem in case of a car with a sunroof, because the roof panel still does have some metal around the glass. Seen below is the example of the Panaromic sunroof of the Hyundai Creta and the non-panaromic one on the BMW 3:




The current should be able to travel through the body of the vehicle using the metal of the roof panel that surrounds the sunroof, just like it travels around the windshield and windows through the pillars:


However, I think this could pose a problem in case of convertibles or cars with a top made entirely out of glass.

Another really interesting example is the 1956 Buick Centurion. This car has a top made fully of glass, but even here you can observe a metallic frame that should allow charge to travel through the body in case of a lightning strike:



Another point that comes to mind is that what if the beam of lightning falls exactly on the glass area of the roof?
The answer to this would be that since the metal surrounding the glass has a higher affinity for the current, it might attract the current towards itself, and hence divert it away from the glass.

All images taken from respective books and the internet. Credit to the creator.

[rpm]

Originally Posted by abhishek46

I would like add one more question. Can the sunroof (esp. the Panoramic ones) survive a hit from a small sized coconut?

I would like to know the same too.

Originally Posted by saikarthik

Thank you for posting an interesting topic, and let the debate start for good.

This is the first time I am reading about a sunroof going ka-boom! I think these might be few probable cases in my opinion.....

Thank you for participating and making the discussion more interesting and engaging. You make some valuable points about probable causes.

Originally Posted by 88_TANK_88

With knowledge of physics limited to schooling and a couple of years in college, ( Public Advisory: I was not a very good student).........
As far as glass is concerned, the most vulnerable would be rear windscreen with defogger wires through it. Tyres do often burst and occasionally catch fire.

I was a very mediocre student too You make an interesting point about rear windshield, never thought of that.

Originally Posted by Sanidhya mukund

I had never thought I would be opening my 12th grade books again, not in the least Physics. But your thread really tickled my brain.

This is what a book called S.L Arora has to say about this:

A figure from the 12th grade physics NCERT:

Going by the above, the body of a car is taken to be a hollow conducting sphere..........

Hence by this logic, it should also not be a problem in case of a car with a sunroof, because the roof panel still does have some metal around the glass...........
All images taken from respective books and the internet. Credit to the creator.

Those names do bring back some memories. Thanks for posting a detailed answer with relevant pictures and sources.

[GTO]

Originally Posted by abhishek46

Can the sunroof (esp. the Panoramic ones) survive a hit from a small sized coconut?

Small coconut from a low falling height should be okay IMHO. I'm the official coconut expert on Team-BHP because my building is full of coconut trees and I have replaced a minimum of 10 windscreens in the last 15 years or so . I now have a protective net parked above all my parking spots (visible in this pic).

I would like to believe that the sunroof's glass is far stronger than the windscreen as:

1. Coconuts have broken many windscreens in my building, but not a single sunroof (*touches wood*).

2. All my cars have dents on the roof from falling coconuts. No sunroof damage till date.

3. The sunroof's glass itself feels much thicker & stronger than the windscreen's.

However, give the coconut some size, weight & a lot of (falling) height, and I guess it will break the sunroof. Example posts:

Originally Posted by ajmat

A friend of mine parked his Volvo XC90 under a coconut tree. It cost him Rs 70000!

Originally Posted by navin_v8

This is really for one who has parked their beloved car below a coconut tree. I remember a friend's boss who had a Mercedes Benz S class with sun roof. The said car was parked in an open parking lot of a commercial building, suddenly a coconut fell from the tree which was directly above the parked car. The damn coconut shattered the sun roof glass and landed on the centre console thereby damaging both the sun roof and the centre console. My friend told me his boss had to claim insurance in lakhs considering it was a Merc S class.

[Adam]

Originally Posted by abhishek46

I would like add one more question.

Can the sunroof (esp. the Panoramic ones) survive a hit from a small sized coconut?

Lighting is an interesting topic, but coconut is in whole another level.
Depending upon the height of coconut tree, built quality of coconut combined with our luck there is high chance of breakage.

Coming to lighting cars are safe with windows closed, basically sunroof if a window and unless its open ,car can act as a Faraday's cage and can protect passengers from lightning.

[for_cars1]

Originally Posted by abhishek46

I would like add one more question.

Can the sunroof (esp. the Panoramic ones) survive a hit from a small sized coconut?

Having first hand experience of a coconut on a windshield, it may be a small sized coconut, but when falls from about 30 to 40 feet, it has significant destructive force. It caused the laminated tough windshield to cave in and completely shatter.
If it falls on a panoramic sunroof from considerable height, it will just cave in and could endanger the occupants.

[turbo_delight]

If lightning stucks the car, with or without sunroof, the end result will be same. You won't be able to come back here to post anything.

Questions like these are the outcomes of WFH

[Jeroen]

Originally Posted by turbo_delight

If lightning stucks the car, with or without sunroof, the end result will be same. You won't be able to come back here to post anything.

Contrary; Likely, it won’t affect you at all! Look at the video with Hammond. He is happily sitting in that car whilst it is being pounded with lightning bolts!

It would be a problem in a soft top car. And preferably you would not be touching any exposed metal. But as long as you sit tight and wait it out, you should actually be fine.

Apart from being inside a sturdy building, being in a car during a thunderstorm is likely to much safer place than anywhere else!

Jeroen

[androdev]

I think having a sunroof is safer because you will be able to see the incoming lightning bolt and take evasive action.

[itsmb]

Originally Posted by androdev

I think having a sunroof is safer because you will be able to see the incoming lightning bolt and take evasive action.

The act would be over before you blink, let alone take any action. If God shows some mercy and you see an incoming best action would be to stay put and not touch anything.
Also lightning strikes in a flash, I do not think anyone would be able to see an incoming strike.

[Jeroen]

Originally Posted by androdev

I think having a sunroof is safer because you will be able to see the incoming lightning bolt and take evasive action.

Only if you have lighting fast reaction!

While the flashes we see as a result of a lightning strike travel at the speed of light (670,000,000 mph) an actual lightning strike travels at a comparatively gentile 270,000 mph.

More importantly; there is no lightening bolt coming down from the sky!!! or at least not always. What we actually see the real big flash, is a lightening bolt shooting up to the clouds. Happens in less than milliseconds so way to fast for the human eye to catch which direction it is travelling!!

Jeroen

[srishiva]

@androdev is just joking. I hope If only sound and light could swap their speeds !

When inside the car with lightning striking your car, you should not touch anything that connects to the metal body from inside. As Hammond does, just sit on the seat without touching any metal.