science experiment for kids of all ages involving water density and how it is affected by temperature

Homeschool Science Experiment : Water Density

Easy Science Experiment for Kids Involving Water Density

This science experiment is super easy and does not require much time and uses things you probably already have on hand. This science experiment will help your child understand density, or rather how temperature can affect density. What would happen if we place a jar of hot water in cold water? What about the other way around?

Supplies for Density Experiment

supplies needed for water density science experiment. large glass, small glass, string and food dye
Supplies for your water density science experiment

Large glass container – Hopefully tall enough to get a good view of what is going on. Ours was on the short side but it still worked.

Small glass container – Make sure your small container will fit inside the large container. If you use a mason jar it will be easy to use the string on it.


Food Dye

How to do the Experiment

Prior to the experiment you can have your kid write out their question and hypothesis for the science experiment today.

1.Fill your large glass container up with cold water. Throw a few ice cubes in to cool down your tap water or get some out of the fridge. Leave room for displacement.

water density experiment showing a large container filled with cold water
Put cold water into your large glass container for science experiment.

2. Tie a string around your small jar.

Tie a string around small jar in water density science experiment
Tie a string under lip of mason jar


3. Place hot water in your small jar and a few drops of food dye. I warmed ours up in the tea kettle yet, it was pretty toasty but not to the point where we couldn’t touch the sides of the jar without getting instantly scorched. I am a little paranoid about glass shattering so I tried not to make it extremes with the cold and hot waters.

place hot water and dye in small jar
Place hot water and a few drops of dye in small jar

4. Carefully lower down your small jar into the large glass container and see what happens.

    • The colored hot water in the small container should come billowing out and swirl up to the top of the container.
science experiment results for water density experiment. hot water rose and cold undyed water is in the bottom
Hot water rises up to the top

5. To do a little comparison we did the same thing again but this time we put the hot water in the large container and the small container had cold dyed water.

    • The colored cold water in the small container should pretty much stay in place.
science experiment showing cold water staying in small jar for second variation of experiment
Cold water staying down in the small container

Have your kids write down their findings and then discuss why this happened.

The Why

Why did the hot colored water rise and stay at the top in the first round of the experiment? Why did the cold colored water stay in the jar in the second round of the experiment? They were both the same thing, not like oil and water. The difference in density has to do with the variation in temperatures with the two waters. The hot water has molecules moving really fast, bouncing off of one another and causing more space in between the molecules, therefore making it less dense, allowing it to float on top of the cold water. The cold water on the other hand has slower moving molecules with molecules closer together, making it more dense, and therefore it will sink.

I hope you had fun with your quick easy science experiment. Don’t forget to check out more posts or subscribe to stay informed of more fun educational ideas. Have fun learning!

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