Last week, our class had a great time discovering some of the scientific principles that govern whether an object will float or sink.
We started off with a simple enough question: will plasticine float? We tried it out by dropping a ball (slightly larger than a golf ball) into a bucket of water. What happened? It sank like a rock to the bottom!
Mr Sanderson then told us a fact which we all knew, but that we hadn't really thought about before. A lump of steel will (obviously) sink in water, but battleships are made from steel and they float...how can this be?
After some thought, we came up with the idea that it must be the thickness and the shape of the material that determines if it will float or sink. We then broke into pairs, were given a lump of plasticine and told to go and try to make it float. After only a few moments, we worked it out - you had to make the plasticine thin, and mould it into a boat shape. We tried it and voila! We had made our plasticine float!
Mr S then set us a second challenge. He gave us access to a box of 2cm wooden cubes and told us to see how many blocks our boats could hold before they did a 'Titanic' and sank to the depths of the bucket ocean. At first, our mighty vessels would only hold approximately 10 blocks, but then we started to modify our boats by making the walls thinner and the bottom (he called them 'hulls') wider and longer. Before long, we were able to place over 20 blocks on our boats.
Being the competitive souls that we are, we then had a competition to see whose boat could hold the most. Finn and Raymond were locked in a deadly battle with Samara, to earn the title of 'Most Excellent and Brilliant Boat Builder'. In the end, both teams ended up with their boats being able to hold 38 wooden blocks. This beat last year's record of 34, which was held by Alka and Shreya.
Now for the 'sciency' bit! - Why DO some things float and others don't?
What causes some things to sink and float? Well, it’s all about something called density. Do you know what density means? Well everything around us is made up of tiny molecules. In some objects tiny little objects called molecules are jam packed together, and in others they are loosely packed together. This is actually what density means. The objects that are jam packed together have a higher density, and the more loosely packed objects aren’t as dense.
Let’s think for a minute about other large objects like a boat, or maybe even an airship. How does this sink and float work? Some boats are massive, and would seem very dense, so how do they stay afloat? Well basically the boat has to push the water aside so that there’s room for it. As it’s so heavy it actually gets pulled down by gravity. But there’s more to this. Now comes buoyancy, which is the opposite of gravity.
But what is buoyancy? Think about what happens when you put an ice cube into a glass of water. As the ice cube moves some of the water to make way for itself, the water level rises and floats partially in and out of the water. Gravity is pulling the ice cube down and the buoyant force is pushing it up. How far in or out of the water your ice cube stays depends on its density, as that is what the pushing and pulling forces are working against.