One Big Science Eggsperiment to do at Home

science experiment supplies from home: egg, cup measure, and scale

Stuck at home? Are the kids out of school? This invigorating science experiment can be done with materials found around the house. It incorporates physics, chemistry, and biology on a visual and kinesthetic level (aka learning by doing), making it easy for kids to grasp concepts and do their own scientific investigation. We call it:

Floating an Idea

Needed: 

  • 1 or more fresh, raw eggs
  • 1 measuring cup
  • 1 scale that measures grams
  • Water
  • Salt

Step 1: Get to know your subject

Retrieve an egg, and ask the kids if they think they can break it by squeezing it as hard as they can. Encourage them to hold the egg over the sink and give it a squeeze. It feels hard as a rock! Eggs are sturdier than they look, built to be sat on by their mothers for weeks without breaking. (Three weeks for chickens.) 

Now you know something new about eggs. It doesn’t have much to do with this experiment, but it has a way of bringing the family together to learn more.

Step 2: Discover a scientific law

Can eggs float? Ask the kids what they think. Eggs are just too heavy...right? Have the children help you find a cooking pot and eggs, and put the eggs in the pot. Next, just add water.

If the eggs are fresh, they will sink to the bottom. If they’ve been in the fridge for a while, they will start to lean upward as if one side is attached to a string. If they immediately float to the top, they are too old to eat. In fact, this difference is so important that it splits this experiment down a crossroads between physics and microbiology.

If the eggs float: 

It’s time to segway into a microbiology lesson, at least until you can find fresher eggs. Fresh eggs are full of nutrients, but as an egg waits for weeks to be eaten, the nutrients are eaten by microorganisms, digested, and expelled as gas. That’s why it’s so important to eat only fresh food, and to cook eggs before eating them.

To get an idea of what’s happening on the inside, hard boil an expired egg for 10 or more minutes, then crack it open. There will be gaps where bits of egg have been eaten and replaced with gas, making it lighter than the surrounding water. Note: The expired egg is not safe to eat.

If the eggs stay at the bottom:

It’s time to add the secret ingredient: salt! Have the kids add salt by a spoonful at a time, stirring afterwards. It will take about 5 spoonfuls for the magic to happen. Save your container of salt water — you’ll need it later.

With enough salt in the water, the eggs will float to the top. You have just discovered a scientific law, like that things fall when you drop them (gravity).

Eggs sink in fresh water, and float in salt water. But why? Now comes the investigation phase. 

Step 3: Create a hypothesis

Ask your crew: Why do eggs sink in water but not sink into the ground? You might get some confused looks, and a response like “because there’s no room for the eggs to go.” This is actually fairly accurate. The salt makes the water more dense so the egg, in a sense, has nowhere to go. It’s supported by the water just like it’s supported by the ground.

Now you have something to prove: does an egg really weigh less than fresh water, and more than salt water? It’s time to put your question to the test.

Step 4: The great experiment

To solve the mystery, you must determine whether an egg weighs more than fresh water, and less than salt water. But how do you know how much water to weigh?

Fill a cup measure to exactly 1 cup. Gently set an egg inside. (Note: This experiment is more accurate with more eggs as there is a smaller margin of error.)

measuring volume of egg by placing egg in cup measure and reading difference in number of cups

Check the cup measure. Subtract your new measurement from 1 cup. Now you have the volume of your egg. Be sure to write it down!

Now to measure the weight of your egg. Make sure your scale is set to grams, then gently place your egg on the scale. If using a container, first set the container on the scale and press the button so it says “0 grams,” (this is called taring the scale) then place the egg in the container. Write down how much the egg weighs.

Next, measure your measuring cup. Set it on the scale and press the button so it says “0 grams” again. 

Pour fresh water into the measuring cup. Make sure it matches the same volume as the egg: the number you got from the measuring cup. Set the measuring cup full of fresh water on the scale. Write down its weight in grams. 

Now all that’s left is to get the weight of the salt water. Pour out your measuring cup and dry it out. If you still have the salt water handy from earlier, pour it in, once again using the same volume of water. If not, make some more! Make sure it’s enough salt to make the egg float. Write down how much the salt water weighs.

If your experiment comes together correctly, it will looks something like this:

1/4 cup of fresh water weighs 57 grams, 1 egg weighs 60 grams, and 1/4 cup of salt water weighs 62 grams

Our ¼ cup of fresh water weighed 57 grams, our egg weighed 60 grams, and our ¼ cup of salt water weighed 62 grams. The egg is smack in the middle between the two numbers!

Step 5: Final observations.

Notice how close the weights are to each other. Why do eggs weigh just slightly more than water? This is because, just like us, they are mostly made of water. The few ingredients of life included in the egg, and the calcium carbonate shell, are what make eggs weigh ever so slightly more. 

If the kids are eager for more science experiments, browse our online catalog for science activities.

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