Float or Sink Density Lab
Understand density = mass ÷ volume, and that an object floats when its density is less than the liquid’s, sinking deeper the closer the two densities are.
Before you try
What if the sea were made of honey? Could a steel ship still float?
Try it out
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What happened?
Move a control to see what changes and why.
Objects are treated as solid and evenly dense, and the liquids never mix. Real objects can trap air, soak up liquid or change shape.
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Try these ideas
- Keep the mass the same and increase the volume. When does it start floating?
- Find an object that floats in salt water but sinks in fresh water.
- Compare wood in water and in oil.
Why it works
Whether something floats depends on density (how much mass is packed into its volume), not on how heavy it is. A giant steel ship floats because its shape holds lots of air, making its overall density less than water’s.
A floating object sinks just far enough that the liquid it pushes aside weighs the same as the object (Archimedes’ principle). So an object with half the density of water floats half submerged. In this lab you change mass, volume and the liquid and watch the object settle.
Check your understanding
Question 1 of 3
A block has mass 200 g and volume 400 cm³. Will it float in water (density 1 g/cm³)?
Why does a huge steel ship float?
In which liquid would the same object float highest?
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Test an orange with and without its peel in a bowl of water. Which floats?
- Ask: why is it easier to float in the sea than in a swimming pool?
- Shape a ball of foil into a boat. Why does the boat float when the ball sinks?