Recently, CDT-CMP students from Bath got the chance to take part in “Bath Taps into Science 2018”. This week long festival held at the University of Bath gives school children in years 5 & 6 the chance to try some hands-on experiments demonstrated by researchers at the university. For CDT-CMP, the theme of this year’s stall was “states of matter” which was all about solids, liquids, gases and beyond.

To demonstrate density in liquids and gases, we had a scuba diver clinging on to a plastic straw, submerged in a water. Simply squeezing the bottle makes the diver sink as the air inside the straw “air tank” is compressed, therefore becoming more dense.

Things got a bit messy with a build-your-own lava lamp made from oil, food colouring and indigestion tablets. The idea of this experiment was to show that oil and water are “immiscible” (they don’t mix), however our stall quickly became covered in oil with accidental spillages and leaking bottles! Things got really bad when a particular (theoretical) member of our group asked the question “Hey kids… what happens when you add ALL the tablets at the same time?”

An unusual change of state is when a substance skips the liquid phase and goes straight from solid to gas, known as “sublimation”. An example is dry ice which is solid CO2. This is extremely cold (-78 celsius) but when it heats up, it becomes a gas. By dropping dry ice in water the children got to see the the CO2 gas bubbling as it sublimes and were amazed by the thick clouds of fog it makes as water condenses in the air.

The children’s favourite experiment involved marshmallows and a bicycle pump to demonstrate air pressure. It was really interesting to listen to all of the different answers when we asked the children what was going to happen to the marshmallows inside a plastic bottle if we pumped out all of the air. Some of the wildest answers included floating, bouncing around inside, dissappearing completely or even exploding! However, most of the children guessed correctly that the marshmallows gradually grow in order to fill the space created by the vacuum.

It was really great to see how excited the children were about our science experiments, and also how smart some of their answers were!

A quote from the days:

“It’s magic, we are doing a PhD in Harry Potter” – Aitor, 2018. In response to a 10 year old child’s question about why the marshmallows expand under vacuum.