Why do the colours move?

When water touches the Skittles, something interesting happens.

The colourful coating on the outside begins to dissolve and spread into the water.

Each Skittle releases its own colour, creating the rainbow effect you observed.

But did you notice something strange?

The colours don’t rush across the whole plate. Instead, they seem to travel in organised streams.

Why might that happen?

Why do the colours stop when they meet?

This is the part that surprises most scientists-in-training.

When the coloured streams reach the middle of the plate, they often stop instead of mixing together.

At first glance, that seems impossible.

After all, liquids usually mix when they touch.

So why do these colours sometimes stay separated?

Scientists investigate questions like this by looking closely at what is happening in the water.

Can you think of any ideas that might explain it?

What changed when you added the sugar cube?

The sugar cube created a completely different pattern.

Instead of moving toward the centre, some of the colours appeared to move away from it.

Something in the water changed.

Scientists often discover new ideas when they change just one part of an experiment and carefully observe what happens next.

What do you think the sugar cube changed?

Real-World Connection

Scientists study how substances move and mix in liquids.

These same ideas help scientists investigate:

• ocean currents

• weather systems

• pollution in rivers

• how nutrients move through living things

The Skittles rainbow gives us a tiny window into a much bigger scientific world.

Curiosity Spark

The colours seemed to stop when they met.

But what if you used:

• hot water?

• cold water?

• different sweets?

• a larger plate?

Would the colours behave the same way?

Or would something completely different happen?

Try next

• See another experiment where the invisible movement of molecules creates a visible effect → [The Pepper Escape]

• Explore how concentration differences drive a completely different kind of colour change → [The Colour Climb]