A little porosity can go a long way. Without it, everything would just be big solid blocks of… stuff, whatever the thing in question is made of, I guess. As it is, there’s almost nothing in the world that’s really, completely, 100% solid. Again, porosity goes a long way, and when combined with permeability, makes for a fun and easy science experiment. Check it out!
Lots of Jars Being Used Around Here Lately…
For this Demo Science science demo, you’ll need a large jar, good-sized pebbles or landscaping rocks (like stylish landscaping, not functional landscaping), fine-grained sand, and water.
First, fill your jar with rocks and ask your students if they think the jar is full. They’ll probably say it is full, because kids are dumb. Explain to them that it is not, since there’s actually a bunch of open space betwixt the stones. Ask them how much, if any, water can be added to the jar.
Once you’ve reached a general consensus, start slowly filling the jar with water. Have your students observe the movement of the water as it courses between the stones. Be sure to keep track of how much water actually does go into your jar, or else what’s the point?
Then, either have another jar at the ready or pour out the water and rocks. This time, fill the jar with sand, and repeat the process above. Ask your students how much more/less water will fit this time. Observe and, again, monitor how much water fits into the “full” jar.
Big Jar O’ Science
Your students will be able to observe the water flowing quickly and easily between the pebbles as you fill the jar. Larger materials, like the rocks, have higher porosity because they don’t fit or pack together as closely as smaller materials, like the sand, and therefore leave larger spaces or voids between them. There’s your porosity, man!
The water in the sand jar shows how permeability works. Permeability is, of course, a material’s ability to transmit fluids. The water will flow much more slowly into the sand than it did the pebbles, because there is almost no space between the grains of sand. However, the water will eventually makes its way in there. It may take longer, but you’ll likely be able to get almost as much water into the sand-filled jars as you did in the rock jar.