Science Questions

If my car gives me static shocks whyis it a good place to be during a lightning storm?

Tue, 6th Sep 2016

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Question

Ari asked:

During lightning the best place to be is in your car ?

If that is correct why do i get a static shock sometimes when i touch my car ?

 

its not grounded due to the tyres ( note i disconnected the battery earth wire and it still happens

 

thanks

 

 

 

Answer

Caroline clears up confusion about cars in thunder storms...Smart car

Caroline - It is a good idea to be in your car in a lightning storm. So, static shocks happen when two materials rub against each other and charge transfers from one to the other. So this could be when you sat in your car wearing some synthetic material and it rubs against a car seat and you build up a negative charge and then you innocently reach out to grab your car door handle and the negative charge from you discharges through the car and makes a sort of nasty shock. But lightning, itís a good idea to be in your car if there's a lightning storm because if lightning were to strike the outside of your car, the lightning would travel through your car body and not actually harm you. Thatís because the car Ė well provided your car is made of metal - the current will want to travel through that because current likes to go through the path of least resistance so it will travel through the car, to the ground, shielding you. This is often referred to as a faraday cage.

Kat - Youíve got rubber tires as well. Is it something like you're meant to wear wellies as well in an electrical storm?

Caroline - So, the rubber tires thing is quite often Ė itís been a myth. Itís an easy answer to why you should get in your car but thatís not really why because the current does still flow through the tires to the ground. It does discharge. But yes, if you're wearing rubbing shoes, rubber is an insulator so you're slightly more protected from an electric shock. Because it just makes a bit more of a resistive path for the current to travel and itís less likely to travel through you.

Kat - AdamÖ

Adam - How do I stop getting shocked by my car?

Caroline - So, you could buy a non-metal car which is an option.

Caroline - Or you could wear clothes that sort of build-up static charge less. The cheaper more plastic clothes build up stuff that charge more.

Kat - You're wearing like nylon. Stop wearing the nylon Ď90s.

Caroline - Yeah, nylon is bad plan. I remember I used to have a dressing gown that I could build up such a static charge on by rubbing it against the carpet that if you turned off the lights, you could actually see the little electric discharge if you touched it, so donít wear that dressing gown.

Adam - No driving with dressing gown.

Caroline - No driving in dressing gowns. Go for sort of Ė I'm not sure what materials are not good at building up charge.

Kat - Linens, cottonsÖ

Caroline - Imagine stuff like silk and things like that would be fine. You can get silk suit.

Adam - Silk trousers.

Caroline - Silk suit and a wooden car, and you're absolutely fine.

Kat - No chances of electric shocks.

Adam - Thanks very much.

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If lightning can travel ~100m from the cloud to the car, it will have no problem travelling the 10cm air-gap from the car body to the ground.

https://youtu.be/ve6XGKZxYxA?t=1m40s
https://youtu.be/ve6XGKZxYxA?t=1m40s




The static shock from the car isn't caused by the battery. The movement of the car causes it to accumulate charge. The solution is an earthing-strap. RD, Tue, 19th Jul 2016

Most of the shocks you experience in a car are due to the generation static electricity built up by your clothing rubbing on the seat it has no relevance to external lightning syhprum, Tue, 19th Jul 2016

If you are standing on the ground in the open, the lightning travels through your body to the ground, causing electrocution.

In a lightning storm, the car's body acts as a Faraday Cage (assuming it's not a convertible...). The electricity of the lightning tends to go around the metal car body to the ground, rather than through the occupants sitting in the middle of the car.

If you or your car builds up a static charge while driving, sitting in the car is a perfectly safe place to be. It is only when you touch the ground that the charge travels through you to the car.

Also, having the windows closed partially shields you from the deafening bang of a nearby lightning strike.

See: https://en.wikipedia.org/wiki/Faraday_cage evan_au, Tue, 19th Jul 2016



It's the car moving along the road & through the air which causes it to accumulate charge.
Aircraft also ... https://en.wikipedia.org/wiki/Triboelectric_effect#In_aircraft_and_spacecraft RD, Tue, 19th Jul 2016


The tyres are rich in graphite and make good conductive ground connection for lightning - which will travel over the surface of the car to ground and won't trouble you inside. dlorde, Tue, 19th Jul 2016

You are generating the static charge, either by walking towards the car with insulating soles or by moving around inside the car, wearing insulating clothing. When you touch the metal of the vehicle, your static charge flows to earth and you feel the shock of the current flow at your fingertips.

A lightning discharge will flow to earth through the metal and the (conducting) tyres.


Wikipedia has plenty to say about "Faraday cages", including
alancalverd, Wed, 20th Jul 2016

Even Ghostbusters (2016) used a Faraday cage... evan_au, Wed, 20th Jul 2016


Actually it is grounded. The potential of the lightning is in the billion volt range. With a voltage that high current can flow through them. Keep in mind that rubber is not a perfect conductor. Almost all materials have at least a small conductivity to them. PmbPhy, Wed, 20th Jul 2016

Vehicle tyre rubber is heavily loaded with carbon to make it conductive, and half the mass is steel wire. alancalverd, Wed, 20th Jul 2016

Cars are pretty good, but are not a perfect Faraday shield. The windows have, on rare occasions, allowed lightning to hit someone inside the car, but the lightning is strongly attracted to the metal work, so this is rare.

All this assumes you have a metal car of course, if it's made of composites, all bets are off, also soft-top cars! wolfekeeper, Wed, 20th Jul 2016

Pure composites may be glass fibre (useless - it's an insulator) or carbon fibre (explodes). Lightning strikes are common on aircraft so they use metal equipotental bonding wires and tapes to protect composite sections (including wood) but strikes on cars are I think sufficiently rare that they probably aren't bonded.  alancalverd, Thu, 21st Jul 2016

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