With all this warm weather coming up, there’s bound to be a few water balloon fights! When you break out the water balloons, learn some science while you’re at it! Today we are going to figure out whether water balloons sink or float.
Before we start testing, let’s talk a little bit about density. We learned about liquid density when we made liquid rainbows in a jar. In this activity, we found that you can actually layer liquids because some are denser than others.
If you missed it, check it out HERE.
As a reminder, the equation for density is:
What exactly does this mean? If one substance weighs more than another substance of the same volume, then the first substance is more dense. For example, think about 1 cup of water and 1 cup of air. Which weighs more? Clearly, water must be more dense.
What about the same substances at different temperatures? When we learned about air masses we used warm water and cold water to create a demonstration of what happens when two air masses collide. Take a look at this other cool density science experiment to find out why temperature affects water’s density:
As you saw in the video, warm water was less dense than cold water. Because of this difference in density, the warm water rose while the cold water sank.
Now that you know more about density, on to the activity!
YOU WILL NEED:
* Water balloons
* Large saucepan of water
* Hose or faucet
Here’s what to do!
1. Fill a large saucepan with cold water.
2. Drop an empty balloon into the water. Does it sink or float? What does this tell you about balloon rubber?
3. Fill one balloon with air. Predict whether the balloon will sink or float. Think back to what you learned about density.
4. Fill a blue balloon with cold water and a red balloon with warm water. Do you think temperature will affect whether the balloons float or sink? Why or why not?
5. Drop the balloons into the saucepan of cold water. What happens? Record your results.
6. You should have noticed that both balloons still floated. Why do you think this is?
7. Remove the balloons. Now, you are going to heat the water in the saucepan. Turn the stovetop on and leave the saucepan on the burner until the water is very warm, but not boiling. Remove the saucepan from the stove.
8. Once again, fill a blue balloon with cold water and a red balloon with warm water. Drop both balloons in the saucepan of hot water. What happens this time?
9. You should have noticed that the blue balloon sank! Why is this? Think back to the demonstration about water density and temperature.
10. Wait until the water cools off and check back on the balloons. Are they sinking or floating? Why do you think this is?
Extension #1: Test other objects’ densities by dropping them in the water to see if they sink or float!
Extension #2: What would happen if you froze one of the water balloons? Try it with both the cold water and hot water. What do you observe?
Wonder why? Check out this explanation: