The Magic of Sandcastles
By: Tracy Winter, OSU Extension Educator, 4-H Youth Development
Photo: a photo of man and son making a sandcastle. Father and boy are playing in the sand on a sunny day. Getty Images stock.
Have you ever tried to build a sandcastle with dry sand? It just doesn’t work! Let’s find out what is needed to make the sandcastle stick together.
Photo: a photo of loose sand in hands, https://jmlysun.wordpress.com/tag/hands/, formed sandcastle.
Did you know that sand is absorbent? Even though grains of sand are very hard they are made up of pores. Pores are tiny holes normally filled with air when dry. However, when grains of sand get wet, these tiny pores fill up with water. The water in these pores form bonds and hold the grains of sand together. In nature, sand is naturally hydrophilic (water-loving). Water molecules will adhere or stick directly to the sand grains. The water does not react with the grains. Water is not making the sand sticky, rather it is simply helping hold the grains of sand together. When the sand is dry, there are no water molecules to build those bonds, and the sand grains will not adhere or stick together. Let’s experiment with, The Magic Castle Cloverbuds’ Lesson.
Gather your supplies, you will need:
- Play Sand
- Water bottle with a sprayer
- Medium size bowl
- Plastic cup
- Feather or a small piece of paper
- Microscope
Steps:
- Using play sand, explore the properties of sand. Pack dry sand into a plastic cup and try to make a sandcastle. Did the sand hold together?
- What will make your sand work for castle construction? Spread the sand out and add moisture by spraying it with a water bottle. Pack the damp sand into a plastic cup. What happened this time? Why did the wet sand stick together when the dry sand fell apart?
- Look at grains of sand under a microscope. Do sand grains have different colors, shapes, or sizes? Does the size, color, or shape have anything to do with why the sand stuck together when it was wet, but not when it was dry? Look closely at the grains of sand. Can you see any pores? What role do the pores play in helping sand stick together?
- Find out about water tension. Just like wet sand, water molecules are also hydrophilic. Pour some water in a medium-size bowl and place a feather or small piece of paper on the water surface. The feather or paper will float, because of surface tension. The molecules of water bonded, and the feather or paper is being held up by those bonds. We see this all the time in nature – when insects walk on water, they are really walking across the water bonds.
- Can you come up with a theory of why the wet sand sticks together? Here is why: the water on the sand grains bond together and holds the grains of sand in place.
Peer-reviewed by Sally McClaskey, OSU Extension Program Manager, Education & Marketing. She develops and directs educational programs at the Nationwide & Ohio Farm Bureau 4-H Center, and Meghan Thoreau, OSU Extension Educator in Community Development programmatic focus on STEM Education and Career Exploration.
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