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Why does ice float? Have you ever wondered this? Or maybe your kids have asked you why an ice cube floats in a glass of water, and you are not quite sure how to answer? Today I have a fun ice boat science activity to do with kids to help teach them this concept. This would be a great activity to add to any physical science lessons. It would also make a fun summer learning activity!
See also: Sink or Float: Density of Salt Water
Why Does Ice Float?
Ice is water in its solid phase. Ice floats because it has a lower density than water. This is interesting because most things are more dense in their solid state!
Water molecules (H₂O) are made up of covalent bonds of two positively-charged hydrogen atoms and one negatively-charged oxygen atom. As water cools down and reaches its freezing point, the molecules slow down and the hydrogen bonds arrange themselves in in a crystal lattice structure that forms ice.
In its liquid form, water molecules are packed together closely, but are still moving around. When water freezes, the hydrogen bonds form a structure, which is a hexagonal lattice shape. This forces the molecules in solid water to be spaced further apart than liquid water. This increased space results in the lower density of ice. You may have noticed that frozen water expands.
According to the Archimedes Principle, an object will float in a fluid if it is less dense than the fluid. Ice is less dense than water. The lighter ice displaces a volume of water equal to its own weight. The buoyant force from that displaced water keeps the ice afloat on top of liquid water.
Compare the difference with a bucket of water and some rocks. When you throw a handful of rocks into the bucket, the water is displaced by the volume of the rocks. The rocks are more dense than the water, so they sink. Ice does the same, it displaces the water, but it is pushed upward since it is less dense.
This is why giant icebergs and polar ice caps float in the ocean despite their massive size! It’s a good thing, too because it allows aquatic organisms to still survive underneath their surface instead of crushing them if they were to sink to the ocean floor. Since the ice floats and bodies of water freeze from the top to the bottom, fish and other animals will still survive through harsh winters.
Watch How We Made Our Ice Boats Here:
Ice Boat Science for Kids to Teach Why Ice Floats
Now on to the project! Making ice boats is a fun way to demonstrate the concept: of why does ice float? to younger kids. Helping them understand it is great, but doing it with a hands-on activity is even better!
This ice boat science activity is great for kids of all ages to teach them about why ice floats! It’s fun for preschoolers, toddlers, and elementary aged kids mostly. But even older kids could enjoy this if you teach them the deeper science concepts behind it.
How to Make Ice Boats:
To make the ice boats you will need just a few simple supplies:
Water
Small containers- cups or food containers
Sticks – from outside or craft sticks work, too
Leaves, paper or pieces of duct tape to make the sails
Foil or plastic wrap to secure the sticks
A freezer
Food coloring- (optional) you could color the water just for fun if you want.
Fill your containers with water. Add coloring to the water if you want, but this is totally optional. Decide what you will use to make the mast of your boat- a stick from outside, or a craft stick. Even a straw works well.
Next you will need something to secure it while it freezes so the stick is standing upright. I used foil for ours. But plastic wrap would work, using cups that already have lids would work well, too. You could even secure them with some pipe cleaners or wire.
Freeze the water. This takes several hours. I just put it in the freezer overnight.
Once you take the little boats out of the freezer, remove them from their containers. If the ice is hard to remove, sitting out for just a minute or running a touch of warm water around the outside of the container will work well.
Add a sail to your ice boat. You can use leaves pieces of paper or pieces of colored duct tape. Any way you’d like to decorate it will work well. I like using sticks & leaves on ours since we like to release them at our nearby pond. Then there is no litter left behind after. These are just for show and don’t change how the boat will float.
Set your boats free on the water! You can do this in plastic tubs so they are easy to observe, in a bathtub or in any body of water near you. This is so much fun to watch. Some will tip over and some will stay upright depending on the shape. As they melt, they will rotate in the water, too.
We made a few different sizes of ice boats. I wanted my kids to observe if the size affected how they float or how long they last. This could be a variable in your experiment.
This activity is so easy, inexpensive and tons of fun for kids! Have a great time learning why ice floats and experimenting with your ice boats.
Variation: Try this with salt water. It freezes at a lower temperature. This can represent the ocean waters. As ocean water freezes, it actually expels the salt because it doesn’t’t fit into the structure of the ice crystals. Very little salt freezes in with the water. This makes the salt water much more dense around ice blocks since the salinity increases.
See More Related Water Science Activities:
Homemade Toy Rubber Band Boats
Submarine Science
Bathtub Bottle Rocket
