Science Smarts: Pique their interests through summer with some science fun

By Patty Rooks on May 10, 2025.

It is that time of the year, and I know it may be hard for the educators out there to keep the excitement level up in the classroom. Not just the young minds, but ours also tend to wander to the window as we look out and think about the beautiful weather out there and what the weekend is going to be like. It is just a few more weeks now until summer break, so I thought I would share an interesting experiment that will make your students continue to wonder about science. Let’s get started!

*Remember to ask an adult before doing this experiment.

Materials

– HOT water

– COLD water

– Two bottles or cups

– Red food colouring

– Blue food colouring

– Index card

– Large bin to hold all the water (I like to use an XXXL pickle jar)

Procedure

1. To one bottle add a few drops of blue food colouring and to the other add a few drops of red food colouring. Fill the blue bottle all the way to the top with cold water and the red bottle all the way to the top with hot water (hot tap water is fine).

2. Once both bottles are full place the blue bottle (cold) inside the large bin, on the top of the red bottle (hot) place an index card (very important that the bottle be completely full so the card touches the water). Take the red bottle and place the mouth of the bottle over top the blue bottle. Slowly remove the card. What do you notice? Did the water mix?

3. Repeat the experiment, this time put the red bottle on the bottom and the blue bottle on the top. What did you notice? Was it completely different?

What is going on?

If you did not guess it already, this experiment investigates density. Density is a measure of how heavy a substance is in relation to the amount of space it takes up. It is usually measured in grams per cubic centimetre. We know that water has different densities according to its temperature (ice is less dense and floats which is very important in life on earth). This experiment can demonstrate very subtle differences in water at varying temperatures.

You should have observed when the hot water was on top NO mixing took place, the colours stayed put. This is because the hot water on top was less dense. Why is hot water less dense, you ask?

The higher the temperature of water, the more energy the water molecules have and the faster they are moving. This leads to the molecules being further apart and subsequently less dense.

When water is cold the molecules have less energy and are closer together – therefore more dense. So when you put the cold water on top and the hot water on the bottom you noticed rapid mixing – this is because the cold water “weighed” more and quickly displaced the hot water.

So what’s the deal with ice, why does it float? Ice is a weird one, when water cools it becomes denser but when it finally freezes the crystal structure actually places the molecules further apart, allowing it to be less dense and float!

Patty Rooks, senior scientific consultant PRAXIS, “Connecting Science To The Community.” Contact Praxis at praxis@praxismh.ca, http://www.praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook. Address: 12 826 11th Street SE, Medicine Hat, AB, T1A 1T7 Phone: 403-527-5365, email: praxis@praxismh.ca.

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