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!
This week’s experiment will show you how a submarine works using just a water bottle and a ketchup sachet.
Take a large (2 litre) plastic bottle and fill it with water
Test a few ketchup sachets in a bowl of water to see if they float, not all of them will have an air pocket in.
Add an unopened sachet of ketchup to the bottle. The sachet should float, but if it doesn’t, try adding some salt to the water. Salt increases the density of water, making the sachet float better.
Make sure the bottle is full of water to the top.
Screw on the top very tightly and squeeze the bottle hard.
The sauce submarine will sink to the bottom. If you let go it will float back up.
You can challenge other people to get the sachet to the bottom, lots of people will try and shake it or turn it upside down!
This experiment is all to do with how things float, or the buoyancy of an object. Water pushes up on the ketchup packet with the force equal to the weight of the water that the ketchup packet pushes out the way. If the displaced water is heavier than the sachet, then it will float because it is less dense than the water.
When you squeeze the bottle you apply pressure to the liquid inside. Liquids cant be compressed (squashed) so the pressure is transmitted to the sachet. The ketchup sachet has some nitrogen gas in (to keep it fresh). The gas is compressed and the sachet sinks and therefore displaces less water and sinks. As soon as you let go the sachet expands again and floats.
Submarines use similar systems to allow them to sink and float easily.
This week’s experiment will show you how to create the 1960’s invention – the lava lamp – at home!
You can create your lava lamp in a beaker, a glass or a plastic bottle, whatever you have lying around that you can see through.
Start by filling your container 1/4 full with water and add some food colouring of your choice.
Add oil until its nearly full to the top. Wait a minute or two and the oil should separate out and sit above the water.
Drop in a Alka-Seltzer or any other effervescent (fizzy) tablet and watch the bubbles rise.
Oil floats on top of water because it is less dense and water molecules stick closely together due to their hydrogen bonds, making it difficult for the oil to mix in.
The tablet is more dense than the oil and the water so sinks directly to the bottom. There it reacts with the water to produce the gas, carbon dioxide (CO2). CO2 is less dense than both the water and oil so it rises to the top, carrying some water molecules with it, these are the bubbles that you can see. The bits dropping back down are the water molecules sinking again once the gas has escaped.
A real lava lamp uses wax that is heated by a bulb. The hot wax expands, becomes less dense than the water and so rises. When it cools, it shrinks, becomes denser and sinks.
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.