Today we are looking at materials which absorb water, in particular sponges.
What you need:
- A bowl or tub of water
- Absorbant materials, such as sponges and wash cloths.
- Non absorbant materials, such as plastic blocks or pencils.
- Place the sponge in the water first to demonstrate how it absorbs the water. Does a dry sponge absorb better than a wet sponge? Can you hold the wet sponge up in the air without the water escaping?
- Try the washcloth and show how it does absorb some water, but cannot retain most of it.
- Place the plastic blocks and other non absorbant materials in the water and see what happens.
The Science Bit
Sponges are made of loose fibers with lots of space between them. The holes between the sponge fibers absorb the water, and so the sponge material swells up with water. This stops the water coming out of the sponge when you lift it out of the water. When you squeeze the sponge you are forcing the water out of the holes in the sponge.
A wet sponge will absorb more water than a dry sponge as water molecules are highly attracted to one another.
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