Food Coloring and Fluid Mechanics

MATERIALS:

• food coloring
• clear glasses
• water

Food coloring and water is a great way to introduce children to some basic concepts of fluid mechanics. We got out six glasses, which we filled with water.

First, the kids tasted the water in each glass to see if it tasted the same. I’m not sure what they concluded, since they definitely drank more water from some glasses than others.

I wanted to do the water and musical notes trick, but our thick IKEA glasses didn’t sound very musical. Crystal glasses work beautifully, if you have them.

Next, we put some food coloring in each glass. We did a little color mixing (red and yellow to make orange, and blue and red to make purple). We talked about fluid density (the food coloring is denser and therefore sinks to the bottom) and fluid dispersion (looking at how the food coloring spread through the water). No idea how much of it Emma got, but they were both very tolerant of their geeky mom, although I’m not so sure about Johnny’s expression in this picture. And if you’re wondering, the thing in Emma’s hair is a sticker.

Then we stirred the food coloring in completely and arranged the glasses in rainbow color order. This would have been a good place to illustrate wavelength differences in color by filling glasses with corresponding amounts of water (the most water in the red glass since red light has the longest wavelength and the least in the purple glass since it has the shortest) but we didn’t do this. Maybe next time. I don’t think it would have worked this time, anyhow, because Johnny was comparison tasting the different colors of water.

We ended the activity by pouring all of the glasses of water into a white bucket to see what color we got when they were all mixed together (brown).

Most importantly, everyone had fun!