Make a prediction: Will the object float or sink? Explorations on density.

This week in science, The Super Lollipops were asked to predict whether certain items would float or sink in water and then devise a hypothesis as to why.


Objects float and sink? BUT WHY?


We primarily explored density, but buoyancy was also addressed. Those are big words, so The Super Lollipops were tasked with understanding them.


(Next week, we will explore those two concepts further and also include surface area and displacement as we consider how boats are built to float on the water.)




Every object is made up of molecules, which are teeny tiny and can only be seen with a special type of microscope.


In an object like a rock, or a penny, the molecules are squished very tightly together.


In an object like wood or a piece of foam, the molecules are spread out and farther apart.


Density is how closely all molecules are pushed against each other in a space.




Objects that are more dense than water will sink.


Objects that are less dense than water will float.




Items that are less dense than the water float. They do not sink. They are buoyant.


Items that are denser than the water sink. They are NOT buoyant.


 What about items that are hollow inside, like a bottle? They can collect air, which is less dense than water, so those objects will float. But what if the item fills with water? It will sink.


Questions that were asked by The Super Lollipops as we explored density and buoyancy:


What if something has a hole in it? What will happen?


What happens if water can get inside of a lid? Will it still float, or will it sink?


What happens if the item is bigger? What about if it weighs more?


Why does that one big piece of wood go further down (in the water), and that cork stays further on top (of the water)?


That wood is from nature, and the lid is not real (man-made). It is metal. Does that make them different in their density?