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You probably already know that some things will float in water and some will not. Do you know why that is? Sometimes the best way to find out if something will sink or float is just to try it--and that is exactly what you'll do in this experiment! Gather up some objects from around your house to test their sinking or floating abilities. Make sure all of the items you pick can get wet!
Even though some of your items seemed very light (things like a paperclip or a button), they still sank in the water. Some objects that might have seemed sort of heavy (like a wooden block) probably floated. That is because whether an object sinks or floats in water doesn't just depend on its weight or size. It also depends on its density. Density is a measure of how solid something is. All things are made up of tiny particles called molecules. If the molecules inside an object are very close together, the item is solid, or dense. If the molecules are farther away from each other, the object is less dense, or less solid. An example of a very dense item is a penny. A cork is less dense.
A penny, paperclip, or button sank because the materials they are made of (metal for a paperclip and penny, plastic for a button) had more density than water. (Their molecules are closer together than water molecules are.) A cork, piece of wood, or Styrofoam floated because those materials have less density than water. All the objects that were less dense than water floated in the water! Objects that were more dense than the water sank.
Do you know why oil floats on water? Would an object that sinks in oil be able to float in water? Try this experiment to find out and learn more about density.
The corn syrup was the most dense liquid, so it sank to the bottom of the cup. The water was less dense than the corn syrup, but more dense than the oil, so it settled on top of the corn syrup. The oil was the least dense, so it floated on top of the water!
The objects that you dropped into the cup had different densities. Each object sank into the cup until it got to a liquid that was more dense than it. The cork was not very dense at all, so it floated on the surface of the oil. The wax fell into the oil, but not all the way to the water, so it was more dense than the cork, but not as dense as water. The grape and the raisin fell to the bottom of the water layer, but not into the corn syrup. That means that they were less dense than the corn syrup, but more dense than the water! The penny and screw were very dense; they sank all the way to the bottom of the corn syrup!
To learn more about the properties of water, check out our teaching tip, Learn About Water.