Home » Buoyancy Testing: Will it Sink or Float?
buoyancy duck float

Buoyancy

Buoyancy is the upward force of a fluid on an object that is immersed in it. Put simply, the more buoyant an object is, the more likely it floats in a fluid. In this activity, Ash and Linus test some objects in water, to see which will sink and float. Buoyancy is related to density of materials. You can think of density as how tightly packed the molecules are inside an object. If an object is more dense than water, it will tend to sink. If it is less dense, it will tend to float.

Hypothesis Time

Before we start dropping stuff into water, try to think like a scientist. Based on what you know about water, what do you think will happen when we put these things into the bowl?

  • Wood
  • Plastic toy boat
  • Rubber duck
  • Agate pebble
  • Metal jewelry
  • Tangerine

Do the Experiment

Get ready to test your hypotheses! Collect your test materials, and get a bowl of water ready. You might want to try some other things you have on hand. Set up a data table in your laboratory notebook or science journal so you can record the results of your experiment. It might look something like this.

Object to test in water I predict (sink or float) I observed (did it sink or float?)
Piece of wood
Plastic toy boat
Rubber duck
Agate pebble
Metal jewelry
Tangerine (whole)
Tangerine (peeled)

You can add more rows to the data table and try your own objects! Keep track of your predictions and your observations as you go.

Watch Our Experiment

Here you can see what Ash and Linus tested at ScienceWorks. Watch the video and see their experiment. Also, listen to their thoughts about why things happened. Why did something sink or float? What else could they try to test their conclusions?

Explore More

  • What did you think about your observations?
  • Did you find any surprising results?
  • What happened when you tested the orange with and without its peel? If there was a difference, why do you think that happened?
  • Is there another thing you could test to help you gather more evidence about that?
  • Would the results be different if you used something else instead of water in the bowl?

Part of doing experiments is finding new questions to ask, and new things to investigate! You could compare your results using the same objects, but put them into a bowl of oil instead of water. What would happen then?

Have fun and stay curious!

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