Sink or Float?

An activity that my students (prospective elementary school teachers) do is to interview elementary school children about their ideas about whether things would sink or float. They gather a bunch of objects and ask children to make predictions about whether each object will sink or float. They also ask children to explain their reasoning. Density is a pretty complex topic for children because density is mass per unit volume (or how heavy something is for its size), but children tend to focus on either volume (size) or mass (weight). They might say things like "A log floats because it is big" and "A penny sinks because it is little" or they might think big things sink and little things float or heavy things sink and light things float. After their interviews we discuss children's ideas and talk about the difference between kindergartners and 6th graders' ideas and everything in between.

This year, one of my students asked, "What ideas does your daughter have?"  -- an excellent question. Vivi is quite a bit younger than a kindergartener, so I didn't know what to expect. I didn't even know how easy it would be for her to make predictions or if she knew the words sink and float.  So I did a similar interview with her. I gathered some objects she would be familiar with (some that would sink and some that would float) and asked her to make predictions.

Here is the video...

She had a hard time with the question "Why do you think that?" - in fact she just ignored the question. She was able to make predictions about whether things would sink or float but was learning the vocabulary as we went. In one case she says that something "floated to the bottom." Her favorite part was putting the objects in water.