Beakman's World: Stinky Feet & Bubbles

Beakman’s World Season 1 Episode 12 zooms in on two ordinary things that turn out to be quite strange when you look closely: a soap bubble and a stinky sneaker. In this episode of Beakman’s World, Beakman explains why surface tension pulls every soap bubble into a perfect sphere, then flips the same close focus onto the human foot to show why bacteria and sweat combine to make sneakers smell so gloriously awful. A Beakmania quiz round with the classic sneeze with eyes open challenge sits between the two topics.

In this episode you will discover:

• How to mix a homemade bubble solution with water, dishwashing liquid and glycerin
• What surface tension is, and why it pulls a bubble into a sphere
• Why adhesion makes soap film stick to a rubber band and stretch into any shape
• Why your feet sweat about half a pint (roughly 280 millilitres) every single day
• How bacteria on your skin turn sweat and body oils into the unmistakable sneaker smell
• Why you cannot sneeze with your eyes open, no matter how hard you try

Two everyday surfaces science makes strange

Beakman keeps circling back to the same idea across the episode: a great deal of what makes everyday objects behave the way they do happens at surfaces, where one thing meets another. A soap bubble owes its perfect round shape to surface tension, the force pulling the water film inward at the exact place where soap meets air. A smelly sneaker owes its stink to bacteria feeding on oils at the exact place where skin meets shoe. In both cases the interesting physics and biology is happening in the thinnest possible layer, invisible to the naked eye but easy to see once you know what to look for.

Beakman’s demonstrations

Beakman opens the bubble segment in his La Bubble laboratory, mixing a homemade solution of water, dishwashing liquid and glycerin, then stretches a soap film across a rubber band held by Josie to show that no matter what shape the rubber band takes, surface tension pulls the soap film to fill it. Guest scientist Louis Pearl, billed as Captain Bubbles, blows an actual square bubble on the frame of a wire cube, and Beakman climbs inside a giant bubble to show its shimmering rainbow interior. Later, in the feet segment, he uses microscope views of little rod shaped bacteria to reveal what really lives on skin, then grows a genuine bacteria farm from a swab between Lester’s toes to prove exactly what a shoe worn on a sweaty foot has been culturing all day.

Try this at home

The homemade bubble solution. Into a bucket, pour about half a gallon (roughly 2 litres) of water. Add one third of a cup of clear dishwashing liquid (avoid the opaque hand friendly stuff, which does not make good bubbles) and one tablespoon of glycerin, sold at most pharmacies. Stir gently and, if you can wait, leave the solution to settle for 24 hours before you use it, as the bubbles will hold together far better once the mixture has rested. Any wire loop will do to blow with.

The stinky sneaker bacteria farm. With an adult, boil half a cup of water, then stir in four envelopes of unflavoured gelatine and a teaspoon of sugar until they dissolve. Pour the mixture into a clean jar, cap it, and lay the jar on its side so the gelatine sets in a broad layer. Now take off one sock, put the shoe back on, and go and run around for a few hours until your foot is properly sweaty. Come back, swab between your toes with a cotton bud, then wipe the swab across the set gelatine. Close the jar tightly and put it somewhere warm and dark for four days. When you open it, the coloured patches on the gelatine are colonies of bacteria that were happily living on your foot. Do not open the jar indoors, do not touch the bacteria, and put the whole sealed jar in the bin when you have finished looking.