Soil Erosion
Soil Erosion is when wind or water washes away the top layer of dirt from the ground.
Pour water slowly over a tray of loose dirt tilted at an angle. The water picks up the top layer of fine soil and carries it to the low end of the tray. What remains is the coarser, less fertile material underneath. Rain on bare hillsides does exactly that, moving topsoil downhill with every storm.
Explaining soil erosion by grade level
When rain falls on bare dirt, it moves the soil away. But where grass or plants grow, the roots hold the dirt in place. You can test this with two trays of soil. Pour water on both and see which one loses more dirt.
Projects that explore soil erosion
When water flows over bare ground, it strips away the top layer of soil and carries nutrients with it — that is soil erosion in action. Water-absorbing polymers can slow this process by holding soil particles in place, reducing how much the wind or water can carry off. In one test, an untreated tray lost the most soil by far, while trays treated with polyacrylate kept more dirt from washing away at every amount of water tested.
Bare soil washes away fast when water hits it — wind and water strip the top layer of dirt right off the ground. Plant roots act like anchors. They hold that top layer in place so it cannot wash away. One test used two trays tilted at the same angle. The tray with bare soil lost far more dirt than the one with grass.