Floating lemmons, or not

Observation:
Peeled lemons sink, unpeeled lemons float.

Why is that? Maybe the lemon peel acts like a lifebuoy, keeping the lemon above the water line.  

What we need:

• water,
• small box or a glass container, transparent,
• 1 lemon,
• your lab notebook.

 How to:

1. Fill the container with water, enough to float lemon;
2. Place the lemon inside the container;
3. Observe carefully what happens and record the results in your notebook;
4. Remove the lemon from the water;
5. Peel the lemon;
6. Place it again on the water;
7. Observe carefully what happens and record the results in your notebook.

Attention: Ask an adult o handle the knife

 

What happens?
Peeled lemon sink, unpeeled lemon float.

Why?
Notice that when the lemon was unpeeled it only sunk enough to stabilize its weight. In the picture you can see 1/4 of the lemon off water.

This is due to, at least, two factors, density and porosity.

Density, density depends on lemon weight and volume. But if we peel the lemon it becomes lighter nevertheless it sinks.

Porosity, Lemon peel is extremely porous and when placed in water, the air is trapped in these pores and can not escape, this makes the lemon float. Just enough to compensate its weight.

By simple observation we can see that the peel is made off two areas, a white and spongy one and a yellow and porous one. What if we separate this yellow and white areas?

1. Place the lemon peel in the water. Does it float?
2. Observe carefully what happens and record the results in your notebook;
3. With a knife separate the yellow section from the white section;
4. Try to place the white section in the container. Does it float?;
5. Observe carefully what happens and record the results in your notebook;
6. Now try with the yellow exterior section;
7. Observe carefully what happens and record the results in your notebook.

"The peel white section" floats! The yellow one sinks!
If you look closer you can see that the white section is very spongy, and therefore very light, ie works as a buoy.

In terms of evolution, in which only the fittest survive, we see this floating lemon as a competitive advantage, the fruits may fall from the tree, float in a water course and travel to other destinations and lands where their seeds can proliferate at will.


A step further:

• Use different citrus, like lime or orange.
• Use different fruits like  apples or bananas.
• In nature we can find different thicknesses of peels in lemons. Do the peel thickness affect the outcome?

Et voilá!
Archimedes in action.

Enjoy!