Happy Valentine’s Day! Love can confuse your brain, and so does this week’s Try This Tuesday.
You don’t need any equipment to try this experiment at home – you just need to stare at your screen, or more specifically the + in the middle of the picture below. You can blink but don’t look away.
If you stare long enough the pink dots should disappear!
It looks like the pink dots have disappeared due to a visual phenomenon called Troxler’s fading or Troxler’s effect. if you fix your eyes on a certain point, then anything in your peripheral vision will fade away and disappear after about 20 seconds. In this experiment our sight was focused on the + in the middle of the screen and the the pink dots in your periphery slowly fade and finally disappear. It works especially well in this experiment at there is such low contrast between the light pink dots and the grey background.
This is a type of optical illusion. If you want to see another, have a look at our spinning disk Try This Tuesday.
This Tuesday, you don’t need any equipment to try this experiment at home – you just need to stare at your screen, or more specifically the video clip below:
(don’t worry we aren’t trying to hypnotise you!)
Stare in the dot in the middle of the circle for 20 seconds, you can blink but don’t look away, keep your eyes focused there. After 20 seconds look at someone’s face, if there’s no one around you, get a face up on screen that you can quickly look at.
What did you see?
Hopefully, if it worked you should have seen the face appearing to get bigger. Obviously, it didn’t really grow before your eyes, this is simply an optical illusion playing a trick on your brain.
You see things because your eyes send messages to your brain about different types of light, shapes and movement and your brain makes up an image of the world around you. When you stare at the spinning disk for so long, your eyes continually send messages to you brain to say its spinning. Your brain gets a bit bored of hearing the same message over and over again so kind of stops listening, tunes out the messages and just assumes from now on, this is how it is – everything is spinning.
So when you look away at a face or your hands or anything really, your brain thinks it should be spinning so gets confused and spins the image in the opposite direction, making it appear to grow. After a few seconds, your brain will hopefully catch up and everything will go back to normal.
Here’s a little trick you can play on your friends, or someone you don’t know well enough to already know their birthday…
With the five cards below, you can “guess” anyone’s birthday. Just go through each of the cards in turn and ask them if their birthday (as in the date they were born, not the month, so if they were born on the 17th January, their number is 17) is on the card. Discount the cards their birthday is not on.
With the remaining cards, the cards their birthday is on, add up the numbers in the top left corner and the number you get should be their birthday!
For example, my birthday is the 30th April so 30 in my number. Its on card 1,2,3,4 and not card 0 so you would add up 2+4+8+16=30.
Is it science or is it magic?
Of course it’s science! This actually works on a system called binary, which is the language computers use. Binary is written in 0s and 1s and these together look just like 101001010010010101010 to us but to a computer that might actually mean something.
In this case, when you discount a card, that becomes a 0 and the remaining cards are a 1. So going back to the example of my birthday the cards would read 11110 (reading it backwards) and in binary this means 30.
You will need: large tall glass, bicarbonate of soda (baking soda), vinegar, a candle and some matches
1. Add 4 teaspoons of bicarbonate of soda to the glass
2. Pour in roughly 150ml of vinegar, the mixture will fizz.
3. Light the candle.
4. Once the mixture has stopped fizzing, pick up the glass. Without pouring out the vinegar, gently tip the glass from a few centimeters above the candle. Imagine that there is an invisible liquid inside above the mixture. The candle will go out!
You have produced a gas, carbon dioxide, by mixing the bicarbonate of soda with vinegar (also known as acetic acid). Bicarbonate of soda contains carbon dioxide, but it is attached to other molecules. When you mix it with vinegar the bicarbonate breaks down and releases carbon dioxide as a gas.
The following reaction takes place:
bicarbonate of soda + vinegar → sodium acetate + water + carbon dioxide
NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2
Carbon dioxide is heavier than air so stays in the glass until you tip it over the candle. When you pour carbon dioxide on a candle it stops the flow of oxygen which is needed for a flame to burn, and the candle is extinguished.
Real fire extinguishers also use carbon dioxide to put out fires, it is compressed (squashed) into cylinders and sprayed at fires.
We’re feeling very festive this Tuesday so we thought it was the perfect time to make snow with science. All you need for this one is some shaving foam and bicarbonate of soda.
Simply mix the bicarbonate of soda and shaving foam together in a bowl until you get a powdery consistency.
Pick it up and have a play – you might notice that your fake snow actually feels cold too. This is due to the reaction between the bicarbonate of soda and the shaving foam. The reaction is endothermic meaning that it requires heat to occur, it takes this from the environment and so decreases the temperature around it.
The Science of Shaving Foam
Do you think shaving foam is a liquid or a solid? It’s actually a colloid. A colloid is a substance which has droplets of one state surrounded by another state. There are lots of different types of colloids with different combinations of states making up the droplets and the surrounding. In the case of shaving foam, the droplets are gas and the surrounding is liquid making it a foam colloid.
Today we will be experimenting to see what happens when you put a lighter or a flame underneath a balloon filled with two different states of matter: air and water.
You will need two balloons, some water and a lighter
Blow up one of the balloons with air and tie it up.
Fill the other balloon with a little bit of water, blow it up the rest of the way and tie it up.
Hold the lighter under the balloon with the air in it and see what happens. Be careful as it should pop!
Light the lighter under the balloon with some water in it, be careful to hold the lighter under the part of the balloon where the water is. The balloon won’t pop!
This happens because water can absorb heat a lot easier than air and is a better conductor of heat. Water keeps the heat away from the balloon. This is called its ‘heat capacity’ and is why water is often used to cool things down in places such as power plants. The air is not very good at absorbing the heat, so the balloon heats up and pops!
With Halloween coming up, what better time to make some of your very own slime?
It’s super easy and quick to make – you just need to mix water and cornflour! Start with a little bit of both, if it seems too runny you can add more cornflour and if it becomes a solid then add more water.
You can also add food colouring and glitter if you want to add some sparkle to your slime.
The slime should become a consistency that appears to be a liquid but if you hit it or try to stir it quickly it becomes a solid – so which is it?
Liquid or Solid?
Slime isn’t actually a solid or a liquid – it is a non-Newtonian fluid, this is a fluid that changes its properties when a stress or force is applied.
The slime we’ve made is a particular non-Newtonian fluid called oobleck (yes it’s a funny sounding word – that’s because it is derived from a Dr. Seuss book). The particles of cornflour don’t dissolve in the water, they become suspended in the water and repel each other. Mechanical stress, such as stirring quickly provides energy that overwhelms the repulsive forces, causing the particles of cornflour to temporarily stick together. When the stress is removed, the repulsion returns and the slime becomes liquidy again.
More Non-Newtonian Fluids
1. Custard behaves just like oobleck, in fact if you filled an entire swimming pool with custard, you would be able to walk across it!
2. Ketchup is almost the opposite of oobleck – it become thinner and runnier under impact, that’s why it helps to bang the end of a ketchup bottle when you’re struggling the get some out.
3. Whipping cream acts differently when under a constant and prolonged stress, such as whipping. If you whip cream for long enough it will appear to go from liquid to solid as it becomes whipped cream.
4. Honey similarly needs prolonged stress to change it’s properties. When you stir honey, it will become more like a liquid than a solid.
Yes – you really can make plastic from just milk and vinegar!
First of all just measure out 120ml of milk (it can be any type, we used semi-skimmed). Either heat your milk in your microwave or in a pan on the hob. It needs to get to around 50 degrees C so 1 or 2 minutes in the microwave should do it.
Next add 2 tablespoons of white distilled vinegar to the hot milk and stir – you should see clumps start to form.
Sieve the mixture to remove the excess liquid. Remove even more liquid with a paper towel or piece of kitchen roll.
You should be left with a clump of plastic which you can mould and shape as you please. It should begin to set in an hour.
Plastics are polymers meaning they are made up of long chains of repeated molecules (called monomers). The monomer that we have used is called casein and is found in the milk. When the milk is heated the casein molecules unfold. Adding the vinegar causes them to reorganise into a long chain polymer – making it a plastic.
It might look quite different to the plastics you’re used to today but up until the end of World War II in 1945, casein plastics were commonly found.
This week we’re taking on the science of sweets! Here is a super easy way to make your own sherbet powder at home.
All you will need is:
7 teaspoons of sugar (either caster sugar or icing sugar)
1 teaspoon of bicarbonate of soda
3 teaspoons of citric acid in powder form
Mix your ingredients in a bowl and then take a small amount on a teaspoon and have a taste. It should fizz in your mouth.
Where does the fizz come from?
When you place the mixture on your tongue it reacts with the water in your mouth and produces carbon dioxide, this causes the fizzy feeling.
The reaction occurs because acids, like the citric acid used here, release charged hydrogen particles when added to water. These particles will attack an alkaline (the opposite of an acid) such as bicarbonate of soda. The reaction produces more stable molecules – water and carbon dioxide.
If you pour water onto your mixture you should be able to see the reaction that’s happening in your mouth. You can actually feel the carbon dioxide gas being released if you hold your hand close to the surface.
Can you make a paperclip float in water? Your standard metal paperclip isn’t very buoyant and as you would expect, tends to sink in water. But with just a piece of tissue paper and a pencil you can make a paperclip float…
Place a small piece of tissue paper in the water so it floats
Carefully put your paperclip on the tissue paper without you touching the paper
Slowly use the pencil to push the paper down so it sinks – try not to touch the paperclip.
You should be left with a floating paperclip – but is it really floating?
Technically, the paperclip isn’t actually floating. It is held on the surface of the water by surface tension. Water molecules tend to attract one another and this forms a ‘skin’ on top where the water particles hold tightly together. This surface tension is strong enough to hold the paperclip. But if you poke the paperclip or shake the bowl, you break the surface tension and the paperclip will sink.
Pond skaters also use water tension to walk on water. They have evolved legs that distribute their weight evenly and so are adapted to life on the water’s surface.