Mighty Fortress Erosion Experiment
Huff, puff and blow as hard as you can—do you think you can blow down a sand castle with your mighty breath? Blowing air erodes—wears away—sand and dirt. In Three Little Pigs, houses of straw or twigs were no match for the Big Bad Wolf's strong lungs. Do you think a house made of sand or mud could hold up to wind or water? Let's find out in this erosion experiment.
In some parts of the world, houses are still made from mud and sand, which makes them easier to knock down than homes made of brick and stone. To understand how these materials can (and should) be used to make homes, you'll need to explore how they stand up to the elements.
How does wind and water affect structures made of sand and soil?
- Garden hose
- Plastic cups
- Battery-operated portable fan
- Stopwatch (optional)
- Before you start, take a look at your ingredients. How does the sand feel? How does the soil feel? Do sand and soil stick together easily, or fall apart? Record any observations—things you see—in your notebook.
- Look over your notes, and make a guess about what you think will happen to your soil structure, and what will happen to your sand structure, when you try to knock them down with wind or water. Which "castle" will last longer? Write your guess—called a hypothesis—in your notebook.
- Take your ingredients to a hard surface, like concrete or asphalt. These smooth surfaces will allow you to see exactly how the water and wind affect your structures.
- Create mud by mixing some soil with water. Dirt and soil may look the same, but technically they aren't. Soil consists of sand, silt, clay, minerals, water, air and organic material. And you thought it was just dirt, didn't you?
- Create wet sand by mixing sand with just enough water to make it stick together—like sand on the beach that you use to make sand castles.
- Use a plastic cup to make a structure out of the wet soil; maybe it'll be a castle, maybe just a lot of cups turned over in your own design. Be creative and make your structures just the way YOU like them.
- Repeat Step 6 with the wet sand.
- Next, make similar structures with dry soil and dry sand, for a total of four structures: one made from muddy soil, one dry soil, one wet sand, and one dry sand.
- Now that your creations exist, it's time to see which stand up to wind and water. Use your battery-operated fan to blow air on the four structures. Remember, do NOT use an electric fan—mixing water and electricity is dangerous, so make sure you have the right fan before starting.
- What happens to each of your structures? Draw a picture or write what happened in your notebook.
- Take a garden hose and drop it about two feet away from your structures. Turn on the water for about 30 seconds, and then turn it off. Draw a picture or write what happened in your notebook.
The wind from the fan should have blown away the individual particles of your dry sand structure easily. While all of the structures probably ended up washed away by wind or water, the structures made with soil should have been stronger than the structures made with sand.