Create a Density Column!

Key Concepts

Materials: 
1                large transparent container
3 cups*   water
3 cups*   syrup
3 cups*   cooking oil (of any kind)
4 drops   food coloring (any color)
5                disposable household items (Ex- screw, cherry tomato, candle, crayon, bottle cap)

*Note: More than 3 cups may be used to create a taller density column.

Activity Directions:
  1. Pour 3 cups of water into the container.
  2. Add 4 drops of food coloring into the water and stir the water with a spoon until the water is evenly colored.
  3. Pour 3 cups of syrup into the container.
  4. Pour 3 cups of cooking oil into the container.
  5. Let the liquids in the container sit for 10 minutes.
  6. One by one, drop the 5 household items into the density column. Note the location where each item floats. 
Discussion Questions & Science Explanations:
  1. What is density?
    1. Density is a measure of how much matter is packed into a certain space. 
    2. The equation for density: density = mass ÷ volume. This means that if volume is held constant, the more mass that a liquid has, the more dense it will be, while the less mass that a liquid has, the less dense it will be. 
  2. The oil floats on top of the water, which floats on top of the syrup. What does this tell us about the densities of each liquid?
    1. Liquids that are less dense (and thus have a lower density) will rise and float on top of liquids that are more dense (and thus have a higher density).
    2. Because the oil floats above the water which floats above the syrup, we can conclude that the oil is the least dense, the syrup is the most dense, and the water has a density somewhere in between oil and syrup. 
  3. What does it mean when an item floats just above a certain liquid?
    1. It means that that item is less dense than that liquid that it’s floating on as well as all liquids below that. At the same time, the item is more dense than all liquids above the liquid that it floats on. For example, a cherry tomato will float just above the layer of syrup. This indicates that the tomato is less dense than the syrup and is more dense than the water and oil. 
  4. What is buoyant force?
    1. Buoyant force is the upward force opposing gravity that is exerted on objects inside fluids. As an object is submerged deeper into a liquid, the liquid applies more pressure (buoyant force) to the object.
    2. Once it sinks deep enough, the buoyant force pushing the object up is equal in magnitude to the force of gravity pulling the object down. This is where the object settles. 
Additional Experimentation:
  1. Try using some additional liquids! Some suggestions are dish soap, syrup, or rubbing alcohol.
  2. What happens when you stir the liquids? Will the liquids return to their original locations?
  3. What happens when you push down or pull up an object away from where it has settled? 
Suggested video: https://www.youtube.com/watch?v=I2bjA-3Vn6E

​Published 7.11.2020

Author: Alex Zhang