Lesson plan

Floating, sinking and buoyancy

Do a series of activities that explore the topic.
Science content
Chemistry: States of Matter, Properties of Materials (K-7)

Start with Sinking and floating free experimentation.
Then a selection of activities from:
Dancing raisins.
Cartesian Diver.
Oil and water sinking and floating.

Explain each in terms of floating, sinking and buoyancy:
An object sinks if:
The water it displaces weighs less than the object (object more dense than water).
Force of gravity on the mass is a greater force than buoyancy pushing up.
An object floats if:
The water it displaces weighs more than the object (less dense than water).
Force of gravity on the mass is less than buoyancy.
Object moves until gravity and buoyancy are balanced.

Optional extension to lesson:
When an object is small enough, another force, surface tension can enable it to float.
Surface tension is the attraction of water molecules for each other, so that they make a kind of skin on the surface of the water, that can take a little weight before breaking.
Do the surface tension activities.

Optional art extension to lesson:
Paper marbling


Started this lesson with cans of soda in water. The diet cans are meant to float and the non-diet ones sink, due to their different densities (regular sugar is more dense than diet sugars). But diet cans were not the only floaters - regular coke floated too. Sprite and Canada Dry did sink, as expected. Need to test again with more samples.

Grades taught
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5