Thundering Question - 2

Classical Mechanics Level 1

This fun photo of two brothers with their hair standing on end was taken on the top of Moro Rock in Sequoia National Park in 1975.

The elder brother recalls the day that they hiked to the top of the rock while the weather around them worsened. Suddenly the brothers realized their hair was standing on end, and scrambled to take a photo. Just minutes later the younger boy was struck by lightning, leaving both brothers with third-degree burns.

Lightning is an amazing effect caused by negative charge accumulating at the bottom of clouds, but can be fatal; up to 24 000 people are killed each year by lightning strikes worldwide.

Why did the boys' hair stand up on end just before the lightning strike?

Story and image credit : Daily Mail

The negatively charged mist from the clouds accumulates in your hair An induced charge in the ground draws electrons from your body, leaving your hair positively charged The low pressure of the atmosphere forms a partial vacuum, pulling up light objects The high humidity in the thunderstorm causes positive charges to build up in your hair

4 solutions

Ram Mohith
Jun 18, 2018

When your hair is standing means your hair is responding to the electrical potential difference that has occurred between the earth and the clouds ( static electricity ). The earth (which you are standing on) is positively charged and the cloud base becomes negatively charged. Once the potential difference is large enough nature will seek to equalize the imbalance and a large flow electrons occurs $...\color{#20A900}\text{lightning}$ . The charge from the clouds goes to the earth through a conductor like trees, metal rods, etc. If your hair stands straight it means that you are now acting like a conductor between clouds and earth and you will be hit by a lightening.

You can simulate this by taking a plastic comb and rubbing it on a wool sweater. Which gives it a charge. Then pass the comb near your hair.

So be careful. Be away of this deadly lightening.

This is famous accident. I have ever inspired same problem.

Takahiro Waki - 2 years, 11 months ago

It seems well-established that the Earth's surface is negatively charged under normal conditions. During a storm, the combination of strong up- and down-drafts, along with moisture in the air, create storm clouds with a negatively charged base, via electrons stripped off of rising water molecules, and thus positively charged at the top of the cloud.

The strongly negatively charged based repels the negatively charged particles on Earth's surface down and attracts positively charged particles to the surface. Thus, the Earth's surface becomes positively charged.

Mike Maksymowych - 2 years, 11 months ago

Follow up question, what should I do if I find my hair standing up during a storm, like the two brothers did?

matthew WESSLER - 2 years, 11 months ago

Great question. If you ever feel like your skin is tingling or your hair begins to stand on end during a storm, do whatever you can to NOT be the tallest thing around.

These brothers were in some major trouble because they were on the top of a tall outcropping already, and so were the path of least resistance for the lightning to get to the ground. To avoid this, get to lower ground, and make sure your body is close to the ground. A caveat here is that when lightning strikes, a large current flows through the nearby ground or the layer of water on it. If you're laying down, that current can flow through you from head to toe, causing significant organ damage/burns.

Best approach is to kneel on the balls of your feet and touch your heels together. This minimizes the surface area in contact with the ground, and creates a low resistance path through your touching feet, rather than through your entire body. You might get some foot burns if lightning strikes nearby, but that's not as big a deal as internal organ burns.

Safety first.

Blake Farrow Staff - 2 years, 11 months ago

Is this a real story? , Can I have source pls?

Abdelrahman Mahgoub - 2 years, 11 months ago

Yes. Click the link "Daily Mail" in the question and read the article

Ram Mohith - 2 years, 11 months ago

Blake Farrow Staff
Jul 9, 2018

I was inspired by a follow up question below to post a solution along with a safety primer on what to do, and what not to do in a lightning/thunder storm.

Why the spiky hair?

During a thunderstorm, the strong negative charge which builds up at the bottom of thunderclouds repels electrons on the Earth's surface downwards, leaving the ground positively charged. If you drop two unsuspecting young hikers on the ground, they act as reasonably good conductors. This means the electrons in the hikers are also drawn down into the charged Earth, leaving them (and their hair) positively charged. Once the hair is charged, the Coulomb force attracts the positively charged hair up towards the negatively charged clouds.

Even with some thick-soled shoes, the human body is in electrical contact with the ground, and so the top of your head has the same potential as the Earth. Lightning (and any electrical current) tends to take the path with the lowest resistance (or shortest distance through air) to the Earth's potential, which is from the bottom of the cloud directly to your head. So if you ever feel like your skin is tingling or your hair begins to stand on end during a storm, do whatever you can to NOT be the tallest thing around.

Lightning safety

These brothers were in some major trouble because they were on the top of a tall outcropping already, and so were the path of least resistance for the lightning to get to the ground. To avoid this, get to lower ground, and make sure your body is close to the ground. An important caveat here is that when lightning strikes, a large current flows through the nearby ground or the layer of rainwater on it. DO NOT LAY DOWN . If you're laying down, that current can flow through you from head to toe like a parallel circuit with the ground, causing significant organ damage/burns.

Safety first.

It's a cruel paradox, but if you're near the summit, and if you retreat into a recess in the rocks just below, thinking you'd be safe, the electric current in the rock from a lightning strike can still fry you anyway. This is because electric flow tends to concentrate at "kinks". So, not only avoid obvious summit points, but avoid deep "inverse corner" recesses in the rock as well. See conformal mapping to see how things get "bunched up" at the inverse corners. This is a conformal mapping, which doens't really reflect the fact that electric current will tend to travel closer to the surface, but it gives you an idea anyway:

The safest thing to do is to get away down as far from the summit, or at least do not retreat to the very back of any recess. Corollary: If you're out in the open, and if there's a tall structure, get closer to the tall structure, but not too close. Let the lightning strike the tall structure and dissipate into the ground a safe distance from you.

Michael Mendrin - 2 years, 11 months ago

Good point.

Laura Gao - 2 years, 11 months ago

Great point on the parallel circuit. Of course! Definitely not laying down now.

Marcus Newton - 2 years, 11 months ago

This happened to two friends of mine while standing outside a building during approaching storms. When their hair stood on end, they realized what was happening and ran inside the building in the knick of time.

Ryan Flint - 2 years, 11 months ago

Michael Mendrin
Jul 9, 2018

This explains and illustrates what's going on, how electric charges differentiate in the clouds, which then causes positive charges to accumulate on the ground while repelling negative charges.

Then once the air is ionized sufficiently, lightning can strike. The presence of this growing ionization of the air increases the accumulation of positive charges on the ground, so that when the hair is starting to really pull upwards, get out! The avalanche of air ionization is rapid, and occurs with both negative and positive charges, so that the boys' hair were literally feeding into the postive ionization of the air near them.

So their hair became positively charged because of the surrounding positive air ions instead of the negative charge in the clouds repealing their hair's electrons back to the ground as the staff member said?

Roger AB - 2 years, 11 months ago

I think there are no positively charged air particles.

Roger AB - 2 years, 11 months ago

The boys' hair became positively charged because of the presence of negative charges collecting at the bottom of the clouds. Then both the negative charges at the bottom of the clouds and the positive charges on the ground start to ionize the air itself. The boy's hair were contributing to the positive ionization of the air surrounding them. In other words, the boys' hair were helping create the lightning bolt that hit them.

Air is a poor conductor of electricity unless it is ionized.

Michael Mendrin - 2 years, 11 months ago

oh, I see. Thanks

Roger AB - 2 years, 11 months ago

Why do negative charges accumulate at the bottom of the clouds and not the top?

Kauman Kauma - 2 years, 10 months ago

Lots of things are happening in a cloud that causes charges to move around, but the basic facts are:

1) Friction causes charges to separate, i.e., such as "picking up a loose electron from something else" 2) Heavier particles (like ice particles or water droplets) while falling down pick up electrons from lighter particles in suspension in the air.

So, heavy, negatively-charged particles end up at the bottom of the cloud. The real picture is more complicated than that, but that appears to be the main mechanism.

Michael Mendrin - 2 years, 10 months ago

Marcus Newton
Jul 10, 2018

Electrons are leaving your body through the ground, so your body becomes positively charged. Your hair stands up because you are now being attracted to all the electrons in the cloud above you. As electrons keep leaving your body and going into the ground, there's a point where the potential difference between you and the cloud is large enough that electrons are able overcome the resistance of air and flow through it (air is an electrical insulator). This initial flow of current will ionise the air, quickly making a path from the cloud to your head which is less resistant than the air around it, making it even easier for electrons to shoot down towards you head. And that's when you get lightning

Thundering Question - 2

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