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Rainbow plate

By David, 18 March 2021 Activity

Plate with colourful lollies around the circumference and rainbow pattern in the centre.

Learn about density with a sugary rainbow

Here’s a great excuse to get your parents to buy lollies! All it takes is some warm water to reveal a beautiful rainbow.

You will need

  • Small hard lollies in many colours (e.g. Smarties, M&Ms or Skittles)
  • Small plate
  • Cup
  • Warm water

What to do

  1. Plate with a circle of colourful sweets.Arrange the lollies in a ring around the outside of the plate.
  2. Half fill the cup with warm water.
  3. Pouring warm water onto the plate of sweets.Carefully pour the warm water onto the plate until the lollies are half covered.
  4. Rainbow of colours bleeding from the colourful sweets.Wait and watch!

 

What’s happening?

That’s a beautiful rainbow! To understand where it comes from, it’s good to start with one of the lollies. So grab one and we’ll investigate.

Each lolly is hard (touch it!) and brightly coloured (look at it!). If you lick a lolly, you’ll notice that it’s also very sweet on the outside. This outer shell is made mostly of sugar, with some colours and possibly some flavours too. The centre of the lolly is a bit different, but it doesn’t matter because the water can’t touch it until the outer shell is gone.

When you add warm water to the plate, the sugar coating starts to dissolve. The water near the lolly becomes coloured and sugary. This dissolved sugar makes that water denser, so it tends to fall to the bottom, underneath any clear, fresh water.

So why the stripes? As the sugary water falls off one lolly, there’s also sugary water falling off the lollies to the left and right. These solutions are similar in density so there’s no reason for one to spread into the other. But there’s plenty of fresh water in the middle of the plate for sugary water to fall under, so that’s where the colourful, sugary water goes!

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