My father is a chemist and when I was growing up we used to do experiments at the dinner table all the time. After dinner we’d set things on fire or play with various food items and learn some valuable science lessons. I am so so happy that as my girls get older this “tradition” is taking hold at home.
Tonight at dinner my oldest started talking about how pretty it is when you mix food coloring with milk and drop in some some. “It’s like art” she said. So once dinner was done and the table was cleared out came the milk, food coloring, liquid soap and bowl to put it all in.
She placed milk in a bowl, she insisted on using a cup of milk each time (you can use much much less, waste less milk and still get the same effect.) Then she dropped a drop of each color onto a different section of the bowl. These can stay separated but if you have two kids bumping they table the mix a little and form their own amazing pattern, pre-soap.
Then the magic happened. She drizzled in some liquid soap and WHOOOSH the color fled to the edges of the bowl. Besides just looking super cool this is a lesson on density and surface tension.
The food coloring is less dense than the milk it sits on top but when the soap is dropped into the mix it breaks up fat in the milk and then breaks the surface tension of the water. The soap, which is sitting on the surface, moves with the surface towards the edge of the bowl and away from the soap.
Some of the coloring gets pulled into the milk with the soap and then bubbles up and swirls. It’s pretty amazing to watch. We did it 3 times.