Posted by on Mar 15, 2014 in Rainbow Activities, Science Activities, St. Patrick's Day | 0 comments

This rainbow science experiment is a fun way to explore density.


Rainbow in a Glass

food colouring
5 clear glasses/ plastic cups

Rainbow in a Glass

Here is a detailed video explaining how to conduct this experiment:

My bugs helped measure the sugar into the first four glasses by adding a tablespoon of sugar to the first glass, two to the second, three to the third, and four to the fourth glass. Then they added 3 tablespoons of water to each glass, leaving the 5th glass empty.

Rainbow in a Glass 1  Rainbow in a Glass 2

Next, they put 2-3 drops of food colouring into each of the four glasses (we used purple, blue, yellow and red).

Rainbow in a Glass 4  Rainbow in a Glass 3

After mixing the solutions well, I asked the boys to look closely at each one and predict which coloured solution was the heaviest, or most dense, and why? I used the spoon to scoop up some of each liquid and let it trickle back into each glass. M observed that the purple liquid flowed the slowest and was therefore probably the heaviest. When I asked him which glass had the most sugar in it, he pointed to the purple glass. To test M’s hypothesis, I slowly poured a bit of the purple solution into the fifth empty glass, then I poured the blue solution over the back of the spoon to create a layer on top of the purple layer, and so on. Once we had poured all of the coloured solutions into the 5th glass, we were left with this:

Rainbow in a Glass 7

It was a little difficult to see all of the colours, so we carefully moved our glass to the windowsill in order to investigate it further.

Rainbow in a Glass 9  Rainbow in a Glass 8

The light from the sun helped us to see each layer more clearly. M discovered that his prediction was correct; the more sugar that was mixed into the water, the more dense/heavy the solution was.

When we had finished conducting the experiment, M drew what he observed in his science journal and I recorded his explanation below.

Rainbow in a Glass 10  Rainbow in a Glass 11

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