Bubbles and Smelly Feet
Why are bubbles round? Why do onions make you cry, and why do your eyes shut when you sneeze? And why, oh why, do your brother's sneakers stink? Beakman mixes a bucket of bubble stuff, meets Captain Bubbles and his square bubble, takes a trip through the nose, and grows a jar of foot bacteria you can smell from the next room.
Why Are Bubbles Round?
A bubble is trapped gas. The bubbles you blow are air trapped in a thin skin of soapy water. The skin is stretchy, and it pulls itself as small as it can, like a rubber band let go. That pull is surface tension. The smallest possible skin for a lump of air is a ball, a sphere, so a bubble is round whatever shape the wand was.
Bacteria. Tiny living things that are everywhere, including all over you. Your feet sweat about a quarter of a litre (half a pint) a day, and they give off oils too. To bacteria, those oils are junk food. They gobble them up, and it is their waste that smells. Beakman grows some in a jar of gelatin later on. Memo to you: do not open the jar indoors.
Have a Guess
Have a guess for each one before you tap. Trust your gut.
It fills the shape. The film sticks to every bit of the band (that sticking is called adhesion) and surface tension stretches it tight across the gap, like a drum skin. Only when there is no band to hold on to does the film have to hold itself, and then it goes round.
Yes, inside a frame. Dip a cube made of wire into bubble stuff and films stretch between the edges. Blow a bubble into the middle and the films pull it into a little cube with rounded edges. Take the frame away and it would snap back into a ball at once.
Grooves, patches and a smell. The bacteria from Lester's toes found the warm, dark, sugary jar very much to their liking, multiplied, ate the gelatin and left their waste behind. That waste is what stinky feet smell of. Keep the jar closed when you throw it away.
Fast, Fun, Furious Facts
Eight fast facts from the show and the science. True or false? Tap fast, think faster.
Score:
Best streak:
Let's Find Out
Tap each card to find out more. Four cards for bubbles, two for the nose, two for feet.
Key Ideas
Bubbles Are Trapped Gas
Tap to learn moreA bubble is a bit of gas with a skin round it. The ones you blow are air trapped in a film of soapy water. Beakman's recipe: two litres (half a gallon) of water, a third of a cup of washing-up liquid, a spoonful of glycerine, and a day's rest.
Adhesion and Surface Tension
Tap to learn moreAdhesion is one thing sticking to another, like the soap film sticking to the rubber band. Surface tension is the film's stretchiness, pulling itself as tight and small as it can. Between them they let the film fill any shape you stretch the band into.
Why a Sphere
Tap to learn moreWhen there is no band to hold on to, the film has to hold itself, and surface tension pulls it into the smallest skin that can hold the air. That shape is a sphere: a baseball, a basketball, the Moon, the Earth. A cube holding the same air would need about a fifth more skin.
Bubble Colours
Tap to learn moreThe swirling colours on a bubble come from light bouncing off both the inside and the outside of the thin soap film. Where the film is a different thickness, a different colour shows, so the colours slide about as the film drains. Just before a bubble pops, the film gets so thin it looks clear.
Your Nose and Eyes Are Connected
Tap to learn moreTwo little drains in the corners of your eyes lead down hoses into your nose. That is why a cut onion makes you cry: a chemical from the onion reaches your eyes by way of your nose. And the muscles that make you sneeze force your eyes shut at the same time, so nobody can sneeze with their eyes open.
Eyes Shut for a Sneeze
Tap to learn moreWhen you sneeze, your eyes close all by themselves. It is a reflex, something your body does without asking you first. The old story that your eyes would pop out if they stayed open is not true; the blink is simply part of the same chain of muscle movements as the sneeze.
Bacteria Are Everywhere
Tap to learn moreBacteria are tiny living things, far too small to see, that live everywhere, including all over your body and inside it. Most of them are harmless and some are useful: your body uses bacteria to help digest food. Beakman put the number on your skin at millions per square centimetre.
Why Sneakers Stink
Tap to learn moreYour feet sweat, especially in a warm, closed shoe, and your skin gives off oils too. To bacteria the oils are like junk food. They gobble them up, multiply, and leave their waste behind. The waste is what you can smell. Bacteria are not the stink; what they leave behind is.
A Visitor From History
No scientist from history dropped in this week (Captain Bubbles is alive and well), so meet the first person who ever saw a bacterium.
Antonie van Leeuwenhoek, a Dutch cloth merchant who lived from 1632 to 1723. He ground his own tiny glass lenses, better than anyone else's, and in 1676 looked at a drop of water and saw it swarming with what he called little animals. Nobody believed him until the Royal Society in London checked.
He scraped the gunk from between his own teeth, looked at it through his lens and found it alive with wriggling creatures. Bacteria live on everybody, and he was the first to see them. Beakman's jar of gelatin is the same discovery, three hundred years on, with a smell added.
Try It: Bubble Shapes
Pick a wand, dip it, blow gently or hard, and watch what shape the bubble decides to be.
The film takes the wand's shape while the wand holds it. The moment it lets go it has to hold itself, and surface tension pulls it into a sphere, the smallest skin for the air inside. Every time.
Use What You Know
Time to use what you know. Match the four things to their descriptions, then take on the challenge.
Match Them Up
Tap an item to pick it, then tap the box it belongs to.
Real World Challenge
Your friend's trainers smell terrible, and they say it is because their feet are dirty. Using the words sweat, bacteria and waste, explain what is really going on, and suggest two things that would help (think about what the bacteria need). Then explain why raindrops are round and why a drop of water on a table is not.
What Has Changed Since This Episode
This episode first aired in January 1993. Bubbles are still round and feet still stink, but scientists have found the onion's secret, mapped the zoo on your feet, and made a bubble that lasted over a year.
Now we know: Yes, now. In 2002 scientists in Japan found the enzyme inside the onion that makes the tear-causing chemical, which nobody had known about. Once they knew, growers could breed onions with hardly any of it, and by 2018 tear-free onions were on sale in American shops. Lester's nose can rest.
Now we know: Far from it. In 2013 scientists made the first complete map of the fungi living on human skin and found that the feet, especially the heel, the toenails and the skin between the toes, have by far the richest variety of any part of the body: about eighty different kinds of fungus on the heel alone, living alongside the bacteria. Your feet are a whole ecosystem.
Now we know: Not any more. In 2022 physicists in France kept a bubble intact for 465 days by coating its skin with tiny plastic beads and glycerol, so the water in the film could not drain away or evaporate. Ordinary soap bubbles pop because their skin thins and dries out; stop that, and a bubble can last more than a year.
Show What You Know
Answer these and get an instant tick or a nudge. How many can you get?
Results
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Think About It
Which parts of your body do you think have the most bacteria, and why? Then next time you have a bath, watch the bubbles: are the big ones and the small ones the same shape, and what happens where two bubbles meet?
Episode Discussion
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