In this activity, you and your child will explore how a hard-boiled egg sinks or floats in water with different amounts of salt.
Learning Area(s): Reading and Writing; Science
MATERIALS
- water
- three wide and tall cups or glasses
- hard-boiled egg
- salt
- measuring cup
- measuring spoons
- regular spoon for mixing
- journal, notebook, or a few sheets of paper stapled together
LET'S PLAY
Before the activity, make a hard-boiled egg. Add the egg to a pot and cover it with water. Bring to a boil over high heat. As soon as the water starts to boil, turn off the heat and put the lid on the pot. Let the egg cook in the hot water for about 10 minutes. Then run cold water over the egg to stop the cooking process. Keep the shell on.
Start by asking your child, “What happens when you drop an object in water?” Talk about how it can sink (go to the bottom of the water) or float (stay at the top of the water). Spend some time talking about what makes an object sink or float. You can say something like, “Whether or not an object sinks or floats in water depends on its density. Density is how much space an object takes up (volume) compared to how much there is of what the object is made of (mass).
“If an object is heavy and small, like a rock, it has a high density. When an object has a higher density than water, it will sink. If it’s light and takes up a lot of space, like a white foam cup, it has a low density. When an object has a lower density than water, it will float. Can you think of any other items with high or low density?” Discuss.
“Let’s explore the density of an egg. You will test whether an egg sinks or floats in regular water and in saltwater. How do you think the salt will affect the egg?” Allow your child to share their prediction and write it in their journal.
- Glass #1: No salt. Ask your child to measure and add 2 cups of water into one of the glasses. Then have them drop in the hard-boiled egg and observe what happens. Does is sink? Does it float? Have your child record their observations in their journal. Take the egg out of the water.
- Glass #2: 3 tablespoons of salt. They will measure and add 2 cups of water to this glass and mix in 3 tablespoons of salt until it is dissolved. Let your child drop the hard-boiled egg in the glass with saltwater and observe what happens. Does it sink or float? Ask them to record their observations again. Take the egg out of the water.
- Glass #3: 5 tablespoons of salt. Have your child measure and add 2 cups of water and mix in 5 tablespoons of salt until it is dissolved. Then drop the egg in the saltwater. Discuss your child’s observations and have them record their observations like before.
Your child should observe how the density of water changes as they add more salt to it. They should notice the egg sinking in the first glass of water and floating at different levels in the glasses that have saltwater. After completing the experiment, ask, “What makes the hard-boiled egg sink or float in the different glasses?” and “So what does that mean?” If your child is not able to make inferences about what causes the egg to sink or float, review the concept of density. The egg sinks in regular water because the egg has a greater density than the water. Adding the salt increases the density of the water, so the egg floats because now the saltwater is denser than the egg.
TIPS
- To extend this activity, have your child draw a picture of their findings in their journal.
- To learn more about the concepts of density, review these additional resources:
- book: Floating and Sinking by Amy Hansen
- book: Things that Float and Things that Don’t by David Adler
- video from PBS: How Do Ships Float?
- You can repeat this experiment with other household items to see what is more or less dense than an egg. Have your child record the object and their findings in their journal.