This week, in science, we wanted to find out how quicksand works. We decided to make some. First of all, we collected all the items we were going to need. Corn starch, water, food colouring, a container and a spoon. Then, we added 2 cups of corn starch into our containers and added 1 cup of cold water. We added a few drops of food colouring just for fun. We investigated what happened to the quicksand when it was squeezed and what happened when we stopped. We found out that when a pressure was applied to the liquid it become solid but when we stopped applying pressure the solid changed back to a liquid and ran through our fingers. We really enjoyed investigating it.
The science behind the fun
Quicksand is a great example of a non-Newtonian fluid because it gets more viscous when a force is applied and less viscous when that force is removed. In contrast, Newtonian fluids, like honey, become less viscous when the honey is warm and more viscous when the honey is cold. Our challenge, this week, was to pick up an ice cube in water, using a match stick. The children tried for a long time and tried many different ways. In the end, they gave up and a demonstration was needed. First of all, lay the match horizontal on the ice cube. Sprinkle salt onto the match and wait for a few seconds. Carefully, lift the match and the ice cube will be lifted from the water. Why? When the ice-cube is in the water, it’s beginning to melt. There’s water molecules leaving the ice, or melting, as well as molecules from the liquid getting frozen back onto the ice cube and the liquid in the glass are in a state of equilibrium (a state of balance). Now, adding salt changes everything. Even though there’s salt on the ice, the ice cube is still melting at the same rate as before, but the water around the ice is now diluted by the salt, making it harder for the water molecules to get refrozen back onto the ice, as this happens, the rapid melting of the ice needs a lot of energy. This comes from the heat that’s in the ice and in the water, making the ice and the water colder. There is no salt between the ice cube and the match, it’s just clean water so it doesn’t have any problem refreezing between the ice cube and the match, making it possible to lift