Yeast, friction, pH and goo – all in a day’s work at Einstein’s Kitchen!
Despite the torrential rain, the weekend at Green Man was fantastic. Einstein’s Kitchen was a true success, and I’m looking forward to the next time we get to cook up some science!
I had four smaller experiments on the go in the kitchen – blowing up balloons with yeast, lifting up a jar of rice with only a pencil, testing for acids and alkalis using cabbages, and of course the now infamous Oobleck.
So how do you do all of this? Let’s start at the very beginning…
Can yeast blow up a balloon?
Yeast is a type of micro-organism, so you can only see it under a microscope, but it is a living fungus and commonly used in baking and brewing. In both of these processes the yeast doesn’t breathe like humans do, but survives using fermentation. It uses sugar as a food, and produces CO2 and alcohol. This means that, unlike respiration – where oxygen is taken in and carbon dioxide given out – the yeast produces more and more gas. So, if you trap the yeast in a confined area (like a cola bottle) the extra gas can blow up a balloon!
How do you pick up a jar of rice with only a pencil?
When you first get your jar full of rice all the grains will have lots of gaps between them, full of air. As you push the pencil into the rice, the grains are forced out of the way and will begin to form more ordered arrangements, which reduces the air spaces in the jar. Eventually, the level of rice will drop, as the grains become more and more compacted and closer together – that’s when you top up your jar. As you continue to force the pencil to the bottom of the jar, the friction between the grains of rice, the jar and the pencil increase even more – so much so that eventually (after some perseverance) the force of friction will equal the weight of the jar and the rice. And, hey presto! You’ve lifted the jar!
Using cabbage as a pH indicator.
pH is a measurement of how acidic a solution is – an acid is something with a sour taste, and it has an excess of hydrogen ions (H+). An alkali (also known as a base) has an excess of hydroxide ions (OH-). To learn more about the reactions that happen when you combine the two check out Kay’s blog! Red cabbage has a pigment, or colouring, in it called Flavin. This gives it its purpley-red colour, and is also what can tell you whether something is an acid or alkali. Flavin reacts differently to the amount of H+ ions in a solution, and will turn pink in acids and blue/blue-green in alkalis. You can use it to test out anything you might have at home and even produce a pH scale of your own – showing the range from strong acid, though neutral (the colour doesn’t change), all the way to strong alkali!
If you visited us at Green Man Festival I’m sure you won’t have missed the gloopy mixture we had outside… that was Oobleck. Technically speaking Oobleck is a non-Newtonian fluid. This means it doesn’t act like a ‘normal’ fluid, and doesn’t obey the laws that Newton said all fluids should. These are that they would only respond to temperature (freezing water makes a solid; heating up honey makes it more runny) and pressure (squeezing water out of a water pistol moves it faster). Oobleck also responds to shear forces – when you apply sudden and hard force it behaves like a solid, but when you are gentle with it, it acts like a liquid.
So what is going on – how is it that you can punch it, yet your hand will sink into it if you do it slowly? It’s all about the mixture of molecules in the Oobleck – cornflour and water (twice as much cornflour as water). When you are gentle, and use less force (pouring the Oobleck, or sinking your hand into it) the water molecules can move freely between the cornflour molecules, and they act as a lubricant so it flows like a liquid. When you apply hard, quick force (by hitting or rolling it) the water molecules can’t fill the gaps, meaning the cornflour molecules are pushed together and friction increases – the Oobleck gets stiffer and acts more like a solid.
What else acts like this? Quicksand for one – that’s why the advice is never to struggle if you’re waist-deep in it – you’ll end up causing it to act like a solid and get even more stuck! Oobleck and quicksand are actually thickening non-Newtonian fluids. Thinning ones are those that become more liquid-y when force is applied – a few examples are paint, toothpaste and ketchup (that’s why tapping the neck of the bottle will release the ketchup!).
It’s not just for fun either – thickening non-Newtonian fluids are also useful. A special kind is being tested in body armour – the way it reacts to sudden force makes it perfect for absorbing the impact of a bullet better than standard vests! It’s also used in the transmissions of some 4×4 vehicles, like Land Rovers, to transfer power between the front and rear wheels when the primary driving wheels start to slip.
And, if you were wondering, the name has been taken from the Dr. Seuss book ‘Bartholomew and the Oobleck’, where King Didd tells his servants he is bored of the same rain, snow, sun and fog and tells them to add some variety to the weather. The result is that sticky green Oobleck falls from the sky and buries everything. It is only when Bartholomew tells him to say “Sorry” that the Oobleck stops falling!
Einstein’s Kitchen was an amazing experience, but it would have been nothing without the budding scientists – both the adults and the kids – who came to our stall and participated in all of our activities. I hope we’ve encouraged everyone to think about how much science there is all around them, and to give some of it a try again at home!