Simple Water Displacement Experiement

My oldest recently read the story of the crow and the pitcher as part of her phonics program. At the end we talked about how the crow got the water out of the pitcher, but she wasn't sure she understood. This created an impromptu experiment for us on water displacement.

I started by filling a plastic bottle partly with water (being sure to mark the staring point).  I made sure to use a bottle because the neck would be narrow like the pitcher in the story. Using some decorative pebbles we took turns adding pebbles until the water overflowed.

Now it made sense to the girls that if they added something that sank in the water the water would rise.

So I took it a step further and asked them what would happen if they added marshmallows instead of pebbles. They knew the marshmallows wouldn't sink, but they weren't sure what would happen to the water.

They squished in marshmallow after marshmallow, but the water level didn't change much. We decided that if they added enough the water would eventually be at the top, but there would be so many marshmallows in the way!

This was a fun, impromptu experiment to demonstrate how water displacement and how it differs based on the buoyancy of the object added to the water. It was also great for the girls to see how the crow was able to use a little logic to solve his own problem too!