Density Bottle

Here's what you'll need...
  • 2 cups
  • 1-2 cups water
  • 1-2 cups corn syrup
  • 1-2 cups vegetable oil
  • 2 colors of food coloring (that look good when mixed)
  • 2 stiring untencils
  • 1 plastic water bottle

Question:
Will very small rocks float in water?

Often when we talk about if things will float, we talk about how much they weight, but weight’s not really the issue: Density is.

Everything is made of atoms. Density describes how closely packed those atoms are. If something is denser than water, it will sink; less dense, it will float. So, a very small rock, no matter how little it weighs , will never float because it is denser than water.

Here’s a project that shows how things of different densities interact.

Put a few drops of food coloring into about a cup of water, and put a second color into about a cup of corn syrup. (The three liquids will each take up about a third of the water bottle, so you may need more or less of each liquid.) Food coloring is designed for water-based things, not oil-based things, so the coloring will work for the corn syrup, but won’t work to color the vegetable oil. (The corn syrup and water will mix with each other over time, so choose colors that, when mixed, still look nice.)

Fill about a third of the bottle with vegetable oil, then another third with the colored corn syrup. Does the corn syrup stay on top? Why or why not?

Fill the rest of the bottle with the colored water. Where does it end up in the layers? Is water more or less dense than vegetable oil? How about corn syrup?

Screw the lid back on and you’ve completed your density tube! Now experiment by flipping it over. What happens to the layers?

You can also experiment with other layers – perhaps a half-water/half-corn syrup solution, or a layer of rubbing alcohol, or shampoo and conditioner, or… whatever else you parents will let you experiment with!