Doc. Yard’s submarine secrets for British Science Week
This week marks British Science Week – a perfect excuse for Doc Yard to pull on his lab coat, get back to his secret lab and create some fun kitchen experiments for you to try from home.
Experiment 1: Raisin Submarines
You will need :
- 1 clear glass / jar.
- Bottle of fizzy drink (transparent works best).
- 10 raisins/sultanas.
Method:
Pour the fizzy liquid into your glass or jar. Be careful not to over fill it. Leave a gap at the top. Add 10 raisins into the glass. The raisins should fall to the bottom.
Watch the raisins carefully over a few minutes. You should see them begin to float up towards the surface at different times. When they get to the top they will release the fizz then drop to the bottom of the glass again. This should be repeated by the different raisins at different times. You have made mini submarines!
The Science Bit … what’s going on?
The fizzy drink contains a gas called Carbon Dioxide (CO2). The surface of a raisin is rough, so will trap any gas forming at the surface. As the amount of gas trapped increases, it will displace more liquid, increasing a force called upthrust being exerted on the raisin. It becomes more buoyant and rises to the surface. When the raisin gets to the surface, the bubbles pop, the gas is released, so the raisin sinks back to the bottom of the glass.
Did you know HMS Ocelot used the exact same science to move up and down in the water when on her missions? She would fill her ballast tanks with air to go up, but release the air in her ballast tanks (letting in sea water) to go down.
Experiment 2: Underwater Diving Bell
At first this seems a little bit like magic….
What you’ll need:
- 1 sink of water.
- 1 glass.
- 1 large tissue or piece of kitchen paper.
Method:
Place the screwed–up tissue or paper towel into a glass. Make sure it is wedged at the bottom of the glass, so that it doesn’t fall out when you turn the glass upside down.
Fill a sink with water, so that it is deeper than the height of your glass. Now carefully turn the glass upside down so that the tissue is at the top and rim is at the bottom. Slowly lower it into the water. Keep lowering it, until it is completely submerged (under water). You may get the odd bubble escaping from the glass, but that’s fine, don’t let too much trapped air escape.
Once you are sure that the glass has been completely submerged, lift it up slowly out of the water. You will find that the tissue in the glass is completely dry – even though it has been for a trip underwater!
The Science Bit … what’s going on?
It’s not magic – it’s pure Science. When the glass it submerged under the water, a body of air is trapped within the glass, as well as the tissue. Below the surface, the water in the sink is pushing trying to get into the glass, but the trapped air is pushing back. This is called air pressure. It is strong enough to keep the water out of the glass. This is why the tissue stays dry – even though it has been underwater!
Before Submarines existed, open bottomed machines called ‘Diving Bells’ were used to transport people to the sea floor. Eventually ‘Closed Diving Bells’ were developed that were sealed all around and could be lowered into deeper water. Vessels like this are still used today to rescue crews from submarines in difficulty.
