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Watch how to make fire using a sandwich bag and water

Derek Muller explains how it was done on his YouTube channel Veritasium.
Derek Muller explains how it was done on his YouTube channel Veritasium. Derek Muller explains how it was done on his YouTube channel Veritasium.

How do you start a fire with a sandwich bag and some water?

YouTubers Derek Muller of Veritasium and Grant Thompson “the King of Random” have the answer – fill the sandwich bag with water and turn it into a magnifying glass and allow sunlight to pass through it.

So how exactly does it work?

“The science behind the video is that water has a higher refractive index than air (or vacuum) so light bends when it enters or exits the water,” Muller told the Press Association.

“This is similar to how light bends when passing through glass.

“So essentially using the sandwich bag we’ve managed to create a spheroid of water, which acts as a lens (a magnifying glass).

“This focuses the suns rays to a point (the focal point) which concentrates the sun’s energy on a tiny spot.”

The magnifying effect
The magnifying effect
(YouTube/Veritasium)

When light is localised to a small area, it results in a concentration of heat that can reach incredibly high temperatures.

If a high enough temperature is reached it can cause flammable material to smoulder and begin to burn.

“This increases the sun’s intensity many thousand fold, which increases the temperature of the tinder, which allows combustion to take place,” continued Muller.

“By repeating this procedure and carefully maintaining the embers it’s possible to start a fire in dry grass.”

The pair made another video together, on Thompson’s channel, where they tried to melt glass – take a look.

You can see more from Muller by going to his channel here, or more from Thompson here.