Density line (g/cm³). Anything to the left of the water mark floats. Anything to the right sinks. Pictures are not to scale.
1Predict
The Dead Sea is much saltier than the Red Sea. What happens when you lie back in it? Choose your answer, then lock it in.
2Observe
Choose a water and something to put in it. Then watch where it ends up in the tank.
CWhat happened?
- Water density
- 1.24 g/cm³
- Person density
- 0.99 g/cm³
- Under the water
- 80%
Density means how heavy something is for its size. If something is less dense than the water, it floats.
Tests done: 1 of 3. Try 2 more to open step 3.
More to explore
| Water | Density | Result |
|---|
3Explain
An object floats when its average density is less than the density of the liquid it is in.
The Dead Sea is about 34% salt, nearly ten times saltier than the ocean. All that dissolved salt packs extra mass into every litre, so Dead Sea water is about 1.24 g/cm³ compared with about 1.03 g/cm³ for the Red Sea.
A floating object sinks only until it has pushed aside its own weight of water. In denser water, a smaller volume of water already weighs enough, so less of the object needs to be under the surface. A person floats with about 96% of their body under in the Red Sea, but only about 80% in the Dead Sea: they ride higher.
Your body is roughly as dense as fresh water, so in water that is a quarter denser than that, you float with a large part of you above the surface. Aluminium is more than twice as dense as any of these waters, so it sinks in all of them.