Sink or Float?
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!
What You Need:
- a large container of water (or fill up a sink or bathtub)
- lots of small objects of different weights and materials (plastic, metal, wood, foil, Styrofoam)
- a few larger objects
What You Do:
- Look at the objects you collected. Draw a picture of each one in the boxes on the left side of the worksheet.
- Make a prediction about each object - do you think it will sink or float in the tub of water? (To make a prediction means to say what you think will happen.) Mark your prediction on the worksheet for each item (circle float or sink).
- Drop the objects into the water one at a time. Watch what happens to each one. Did you predict correctly? Circle "float" or "sink" next to each object on the sheet to show the results of your experiment.
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.
What You Need:
- 1-cup glass measuring cup
- vegetable oil
- food coloring
- corn syrup
- small objects (we used a raisin, grape, cork, button, penny, screw, and piece of wax)
What You Do:
- Fill the cup with water to the 1/3 mark. Add 2 or 3 drops of food coloring.
- Add 1/3 cup of corn syrup so that the level of liquid in the cup rises to the 2/3 cup mark.
- Add 1/3 cup of oil to fill the cup to the 1 cup mark.
- Watch what happens. The layers should separate so that the corn syrup is on the bottom, the oil is on top, and the water is in the middle.
- Guess where each of your objects will land when dropped into the cup, then test them out one at a time.
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.