Observations and results
Could you see the spaces between the rocks in the cups? Did the cup with the largest rocks have more air than the cup with the smallest rocks? Did the cup with the smallest rocks have less air than the cup with the medium-size rocks?
This activity modeled the inside of rocks on a much larger scale. Because, in general, larger particles cannot pack together as tightly as smaller particles can, a rock made out of larger particles will usually be more porous than a rock made out of smaller particles. But rocks are not static; like everything, rocks change over time. When enough pressure, or force, is applied to a rock, the pressure can make the rock more efficiently pack its particles. Usually pressure builds up on rock over a long period of time, as dirt and other rocks end up on top of it. You can see how this process, known as compaction, makes the rock's porosity decrease with time.
More to explore
" Rock Properties: Porosity and Density" from Wisconsin Geological and Natural History Survey
"The Rock Cycle: Compaction and Cementation" from The Geological Society of London
"Porosity and Permeability" from eNotes
"Porosity and Particle Size" from Science Buddies
This activity brought to you in partnership with Science Buddies