The physics of hot coals

February 23, 2017

The physics of hot coals

Interested in firewalking but not convinced that “mind over matter” will prevent your feet from burning? We don’t blame you. It’s a scary thought indeed, but you’re much safer than you might think.

Fortunately, you don’t have to take our word for it because science has you covered.

How to not get burned (according to science)

The mystery behind firewalking and why it works can be understood by examining a physical property known as thermal conductivity. Thermal conductivity, essentially, is an object’s ability to transfer energy in the form of heat to another object. Why is this so important? Because it has everything to do with the transfer of heat from the searing, sizzling coals to your naked feet.

Coal is comprised of carbon, which, as it turns out, is pretty terrible at conducting heat. And hot coals, in particular, are covered with a thin layer of ash, which is an even less effective conductor. So what you have is something bad at transferring heat to your skin encased in something even worse at conducting heat (ash).

In addition to hot coals being pretty weak when it comes to the transfer of heat energy, so, too, are your feet. So, if you’re not spending time lingering over each coal and instead briskly walking across them, there’s a low risk of being burned.

Think of it this way: If you reach into a hot stove and touch a piece of metal in it, you’ll be burned immediately because metal is an excellent heat conductor. But if you reach into a hot stove and briefly touch the top of a cake you’re baking, you won’t be burned because, like coals, the cake’s consistency makes it a poor heat conductor.

But poor conductivity isn’t the only thing protecting your feet from hot coals — your brain plays a part in it, too.

Consider this common science experiment: If you fill a paper cup with water and place it over a flame, you might think the paper will catch on fire. But because water can only reach a temperature of 212 degrees Fahrenheit before it turns to steam, and since water’s in constant contact with the cup, the paper can’t get any hotter than 212 degrees — well below the temperature necessary for it to catch on fire.

What does this have to do with walking on coals? The blood flowing through your body keeps you from getting burned in much the same way water prevents the cup from lighting on fire.

This is where your emotional state comes into play. When you’re in a heightened state of fear, your body’s blood vessels constrict so there’s less blood flowing through your feet, and therefore less burn protection. On the other hand, if you’re in the right state of mind — peak state —, your blood will flow more freely, helping to protect your feet.

For those feeling skeptical about their ability to walk across hot coals, it really is about mind over matter (with support from science, too). Master your emotions and you won’t just walk across coals, you’ll master the firewalk that is life.

Image credit © ccaetano/shutterstock

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