Density Curriculum

Section 4—Lesson 13: Dropping an Object into a Liquid: How Does Density Affect Sinking or Floating?

Understanding Goals

Density is one variable involved in sinking and floating.
When considering whether an object will sink or float in a liquid, you have to compare the density of the object to the density of the liquid.
An object made of a substance with a density greater than the liquid will sink in the liquid. An object made of a substance with a density less than that of the liquid will float in liquid, controlling for other variables. If the densities of the liquid and object are equal, the object will suspend.

The role of density in sinking and floating is described by relational causality.
Students' default pattern is to use a simple Linear Causal Model. In the case of sinking and floating, that typically means focusing on the object and neglecting the role of the liquid in the outcome.
The role that the liquid plays is non-obvious. This makes it appear passive and supports an erroneous linear causal model.
Placing the same object in liquids in which it sinks and liquids in which it floats makes the role of the liquid obvious.
Pushing the object down into the liquid and checking to see if it rises or sinks encourages a more active view of the liquid and helps learners to recognize the relational causality involved.