HOW DO YOU MAKE THE PERFECT SANDCASTLE?
Have you tried to make sandcastles with dry sand and they just didn’t work at all? They just collapse! Can you think why this is? What could you add to make the sand more ‘sticky’?
If you add a little bit of water, which should make the sandcastles slightly better. Is it the perfect sandcastle? What happens if you keep adding water? Can you make the perfect sandcastle?
It may take several attempts to get the right combination of sand and water. Can you tell when the sand is ready for building with? Too much water and the sandcastles will fall apart and stick to the inside of your bucket. Too little water and the sand just flows out. If you can squeeze the sand into a ball in your hands and it stays together it makes a good sandcastle.
According to PBS the magic sand to water ratio is one bucket of water to 8 buckets of sand! Can you test this theory? You could use cups instead of buckets. Did you make the perfect sandcastle? Take a photo for the Science Gallery.
WHY DOES WATER MAKE SAND STICK TOGETHER?
You should have noticed that wet sand is much stickier than dry sand. This is because the water forms tiny bridges between the grains of sand, which holds them together. This is due to the surface tension of the water. If too much water is added, water fills the space between the grains of sand and the bridges break down.