How To Make Fire With A Battery

Physics Life Hack Number 2 - Makeshift Firestarter

A simple way to start a fire using the physics of electricity

Let's suppose you're out camping. It's damp and cold and you need to start a fire in a hurry. But alas the matches are wet and impossible to light!

Here's a quick and simple alternative that uses the power of electricity and two items which you might just have laying around anyway: a battery and a gum wrapper. Seen it before? Keep reading to find out the physics behind the hack.

Credit: Cropped image from Martin Cathrae via flickr

The hack

Grab a battery (perhaps from a flashlight) and the foil wrapper from a stick of gum. If you have don't a gum wrapper, try some aluminum foil or steel wool.

Cut a very thin strip out of the foil wrapper, long enough to connect the two ends of the battery. Make the middle of the strip thinner than the two ends. Position yourself close to a pile of kindling and hold the two ends of the foil against the two battery terminals. Within seconds the strip should ignite and if you're quick, you can use this flame to light the kindling.

This video is a quick clip from Grant Thompson's The King of Random YouTube channel, demonstrating the hack.

The same principle works with steel wool, as shown a few years ago by our Physics Buzz blogger, Mathlete. In this case, it's best to use a 9 volt battery, which has the two terminals on the same end of the battery.

How does this work?

This hack demonstrates both the power of an electric current and the greedy chemistry of oxygen.

1. Electric current
When the two ends of a battery are connected by a conductive material, like foil, a current of electrons starts to flow from the negative (-) to the positive end (+) as fast as they can.

Anything that limits their flow is known as resistance. As the electrons flow through the foil, they can collide with atoms in the foil, which slows them down. On the flip side, the atoms in the foil gain energy during this collision and heat up. If the foil heats up enough, it can start to burn.

In normal circuits, the current is small enough compared to the thickness of the wire so that the wire never gets too hot. Instead the heat dissipates throughout the rest of the wire.

But in our case, the width of the foil is deliberately thin so that its resistance is higher (like trying to push a large amount of water through a very thin pipe) and the heat can't easily escape.

2. Oxidation
Now comes the chemistry of oxygen. Every burning process is essentially just oxygen from the atmosphere forcing itself into molecular bonds with atoms from the burning material.

This works because oxygen is extremely attractive to the electrons in other elements and can easily form bonds. This bonding is known as "oxidation" and can lead to the creation of molecules such as water (H₂O), carbon dioxide (CO₂), rust (Fe₂O₃ with water), and aluminum oxide (Al₂O₃). Notice that all of these molecules have oxygen in them. The process of adding oxygen to another element is exothermic, which means it produces heat. Produce enough heat quickly enough and you have a fire.

Oxidized iron, commonly known as rust. Credit: Cropped image from Laitr Keiows via Wikimedia commons

So now to bring these two thoughts together with our battery and aluminum foil wrapper.

In order to get a fire, oxidation must occur quickly. To encourage this, we need a lot of aluminum to be in direct contact with the oxygen in the air. This means we need the foil to be very thin so that it has a large surface area compared to its volume. We also need a bit of energy to jumpstart the whole process. This energy comes from the heat of an electric current flowing through a very thin piece of foil.

Once one part of the foil starts to burn, it can sustain the flame for a short time by the energy produced in the oxidation process, and voila, a makeshift firestarter out of just a bit of foil and a battery.

In practice, this hack can be a little temperamental. Be sure to use fresh batteries and cut your foil very thin. Have your kindling ready to go and also some water nearby, just in case things get a little too hot!