Sink or Float Science Experiment

By contributing writer Marci

Let’s say your little pirate wants to take a trip out to sea, the pool or just the bathtub. He or she will probably need to take supplies. It would be helpful to know which of the supplies sink and which ones float.

Sometimes, kids can just guess and be right. Other times, they are surprised at the result. You can explain to them it’s all about density, but that probably won’t mean much. Try this simple sink or float experiment with your buccaneer to help them learn about and understand density.

Collect random objects of different weights and shapes from around the house, such as marbles, stick matches, Hot Wheel cars, spoons (plastic and metal), grapes, or anything that can get wet.
Use a dishpan, large bowl, plastic container, sink, or bathtub and fill your container with water.
You are going to place each of your objects into the water, but before you do, make predictions about whether each one will sink or float.
Carefully, place each object into the water. Dropping them hard or throwing them will impact what they do without being scientific.
Record if the object floats or sinks and discuss why.

Why Did It Sink or Float?

A determining factor in why objects sink or float in water is density. If an object sinks in water, then it has greater density than the water. Density is a measure of an object’s mass relative to its volume.

The more dense an object is, the more mass it contains in one unit of volume. For instance, if you had two blocks and each one was 1 cubic inch in volume, but one weighed 6 ounces and the other weighed 12 ounces, the block with the mass of 12 ounces would be more dense. It would have a greater density and might cause it to sink.

My 8 year old son explains it this way…

“Some things have more air in them, while others things are more solid. Nerf bullets have air in them, so they float. Keys are harder and more solid, so they sink.”

This is a simplified way to say that objects with a lower density have more space between their molecules, like the Nerf bullets. Keys, on the other hand, are made of dense metal. The molecules in metals are tightly packed. This is what makes them more dense.

Examining Your Results

Knowing what you now know about density. Why do you think you obtained the results you did in your sink or float experiment? What do you know about the density of the objects?

More Homeschool Science Experiments

More Homeschool Science from Marci

Sink or Float Science Experiment