CLASS: 2nd – 5th    20 mins     SESE (SCIENCE)

Curriculum Links - Mixing and Changing

  • Environment - Weather and atmosphere
  • Physics - Heat and temperature
  • Chemistry - Liquids and mixing

Learning Objectives - WALT (We are learning to…)

  • Temperature differences!
  • Our weather
  • Earths atmosphere
  • Density and Color Mixing

Teaching Methodologies

  • Active Learning – Hands on learning with real life examples
  • Experimenting
  • Collaborative work – group work
  • Skills through content – observing, connecting, classifying and predicting.


Do you ever notice that the air above a radiator is hot while the air below it is cold? This is because hot air rises! Hot air is less dense than cold air, meaning it will tend to go upwards, while the colder, denser air goes down.

It is this concept that allows hot air balloons to fly. The flame heats up the air in the balloon and makes it less dense that the surrounding air, causing the whole aircraft to lift!

The atmosphere protects Earth like a big blanket of insulation. It absorbs the heat from the Sun and keeps the heat inside the atmosphere helping the Earth to stay warm. This is why Earth has a stable temperature that's perfect for life.

This rising and falling of hot and cold air is what causes different types of weather. If we keep adding harmful greenhouse gases to the atmosphere, we will heat up the planet. This is what we call Global warming.

Here we will look at how liquids of different temperatures behave, so we can understand what is happening in the atmosphere. The temperature difference in the liquids results in a density difference that has some interesting effects.


Shopping List!

  • Two equal clear containers, like jam jars
  • Water (warm and cold)
  • Food colouring 
  • Plastic sheet

Fill one of the jars with warm liquid, and the other with cold. (The water should not have to be boiling!)

In each jar add a few drops of food colouring. For example, add red food colouring to the warm water and blue to the cold. Mix around until the water is completely coloured.

You may need help with the next part!

Take the plastic sheet and hold it over the cold water jar. Gently turnthe jar upside down and sit it on top of the hot water jar. Slowlyremove the sheet from between, allowing the two liquids to meet each other.

What happens?

As we learned, heat rises, this is why the two liquids start mixing! The hot water is rising to the top jar and mixing with the cold water in it.

Now let's repeat but this time have the warm water jar on top and cold water on the bottom. What happens this time? NOTHING! This is because the hot water is already on top, and the cold water is on the bottom. The hot water is less dense so will float above the cold water.

Over time however, the temperature will even out between the two liquids (which you may see happening at the interface between the two), and they will mix together to become one liquid of the same colour, temperature and density

This is why the surface of the ocean is warm enough for us to swim. The deeper you go the colder and denser the water gets!