Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Lightning safety in a thunderstorm

Learn more physics!

Most recent answer: 08/22/2015
Q:
Why do you think you should not stand under a tree during a thunderstorm? Why do you think you should not stand with your legs apart? Or why is lying down dangerous?
- Sharmyn
STSB, Philippines
A:
Well, standing under a tree in a thunderstorm is probably the action you mention that has the biggest problem. Trees are often the tallest objects around and contain many pointy tips. The electric field is strongest near the pointed tip of an electrical conductor, and so trees often make for great targets for lightning strikes. Trees don't always conduct electricity as well as you do, since people are made mostly out of saltwater. The current from a lightning strike may leave the tree and jump over to you and follow your body on its way to the ground.

Standing out in a field far from trees may also pose risks too. In this case, you are the tallest object around and may be a target for lightning strikes. If you are carrying metal golf clubs at the time, it could raise your risk (this is a common reason people are standing out in flat fields during thunderstorms, is to carry golf clubs. Sometimes such people get struck by lightning). The safest place to be during a thunderstorm is a building or a car. Electricity can flow through the metal sides of a car and not through you.

I'm not so sure about your other questions. Standing with legs together or apart may not make much difference on anything. The only thing I can think of that it might have an effect on is if there is a nearby lightning strike, and there is a large amount of current flowing along the surface of the ground nearby. The ground has a resistivity, and so the voltage changes rapidly from one place to another during the time the current flows. If your legs are apart, the current may decide to flow through you rather than the ground, but this depends on how good an insulator the wet ground is and how good an insulator your boots are. I'd imagine that this is much less likely to cause injury than a direct lightning strike anyhow.

Lying down actually sounds like not such a bad idea, except that during thunderstorms it is probably wet down on the ground. It's best to seek a house or car to stay in during the storm.

Tom

(published on 10/22/2007)

Follow-Up #1: Do cars protect from lightning?

Q:
are you protected from lightning in a car? If so, why? We have always heard that the reason is that rubber tires are insulators. However it recently came to our attention that others have views that differ from ours. Specifically we have heard that the protection is attributable to a so called "Faraday shield" due to the metal in the body of the car. Accordingly a motorcycle offers no protection from lightning. What are the facts? Please respond before the next thunderstorm storm, which is imminent.
- mark cullen (age 61)
los altos, ca. , caliornia
A:
Mark- I don't think that the rubber tires are much help. After all, lightning breaks down air, so it has no trouble getting from the bottom of a car to the ground. On the other hand, if the electricity has a nice conductor to go through, that's the path it will choose. That's the principle behind lightning rods. So the current will go through the metal car, rather than taking a pointless detour through you. It doesn't sound like a motorcycle would help much.

Mike W.

(published on 08/08/2011)

Follow-Up #2: how do lightning rods work?

Q:
I believe the main principle behind the lightening rod is that the pointed metal tip leaks charge to prevent the build up of opposite charge (relative to the underside of the clouds) on the building which decreases the chances of lightening striking there. The connected wires will send the electricity directly to ground in case lightening were to strike.
- Joey (age 20)
Washington, D.C.
A:

That ability to "leak charge" by ionizing some air in the vicinity of the tip actually tends to increase the chance that lightning will strike there. The protection comes completely from the other effect- the current flowing through the rod to the ground, rather than through the building.

Mike W.


(published on 02/19/2015)

Follow-Up #3: why is it not advisable to touch a tent while it is raining?

Q:
why is it not advisable to touch a canvas tent from inside while it is raining?
- harun abdi (age 16)
kenya
A:

I believe this is due to the risk of lightning. Especially if there are not any taller objects such as trees in the immediate neighborhood, the top of the tent may become a lightning target. Your feets may not be insulated from the ground, so you may accidentally ground the top of the tent by completing the circuit with your body. Lightning likes sharp objects: the effect will be the same as a person standing in a meadow. Even if your tent is made of an insulator (say plastic), the lightning voltage is so high that it can destroy that barrier.

Tunc


(published on 08/22/2015)

Follow-up on this answer.