(Physics for ages 5+)
Sand can be found all over the world, but is most often found on beaches and in the desert. Technically it is a type of soil, but it has some special characteristics that can make it especially fun to experiment with.
In the video above, they do an activity that shows the Wet-Sand Effect, a feature that makes water just disappear into sand. Here’s how you can do this at home:
Bowl or tray
2 rubber bands
2 transparent straws
2 transparent balloons
Adult supervision (Adult supervision at all times please)
- First, use the paper to make a funnel and fill your water bottle with sand. Be sure you do this over the bowl or tray to catch any stray sand.
- Next, inflate one of the balloons and stretch its neck over the mouth of the bottle. Turn the bottle upside down and pour the sand into the balloon, and then let the extra air out of the balloon.
- Add water to the sand in the balloon until the sand is saturated or wet all the way through.
- Insert one of your straws into the sand and secure it with a rubber band. Be sure you do this over the bowl or tray to minimize any mess.
- Fill your second balloon with water and then insert your second straw into the water, securing it with a rubber band.
- Holding the water-filled balloon at its neck, pour water into the straw to fill the balloon until the straw is filled halfway. Squeeze the balloon slightly with you hand. What happens to the water?
- Now pour water down the straw of the sand-filled balloon until the straw is filled halfway. Squeeze the balloon with both hands. What happens to the water this time? What happens when you release the balloon?
Grains of sand are actually teeny tiny pieces of rocks that were broken up by water and air over many years. These pieces have jagged edges that do not fit perfectly together, leaving tiny holes (or pores) in between each grain.
When the sand is first saturated, it seems that it is completely full of water, but when you apply pressure by squeezing the balloon, the grains of sand push each other a little further apart (dilates) creating more pores that are filled in by water.
This is called dilatancy of granular materials. When the pressure is released, the pieces of sand move back to their original positions which allowed less room for water, so you will likely see water moving back up the straw.