Why Does Ice Float?

Can be modified to fit multiple ages.

In the past, I have conducted similar labs and units around density and the ability of objects to float. While investigating ice boats, we are going to answer the question, “Why does ice float?” Besides density, buoyancy and displacement can be discussed in this demonstration. For the sake of not repeating myself, if you are interested in learning more about buoyancy and displacement, check out What causes a boat to float? Today we are going to discuss the differences between the solid ice boat versus the liquid water it floats in. We will hit on states of matter, density, volume, evaporation, and even the water molecule! So, let’s get going so we can learn WHY DOES ICE FLOAT?

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How to modify the lesson to suit older students...

Keep scrolling down to GATHER MATERIALS if you have a younger student

On first glance, this lab seems to be suited only for younger scientists, but the science can be extended to meet the needs of older students too. This is because of the uniqueness of the water molecule. If I had a middle school or high school student, I would tell them that the lab is going to show them a special characteristic of the water molecule. Unlike other molecules, the water molecule does not constrict when turning from a liquid to a solid. This is important for many reasons… keep reading. Review these inquiry questions with your student:

What is the scientific name of water?
H2O... let me clarify this. You can not technically write the scientific name for water using a keyboard because it does not allow you to make the 2 behind the H smaller. Refer to the picture below to understand my meaning.
How many atoms are in a water molecule?
There are 3 atoms total. In the scientific name, the H stands for hydrogen and the 2 tells you that there are 2 atoms of hydrogen in a water molecule. The O stands for 1 atom of oxygen in a water molecule.
What is a molecule?
A molecule is a piece of matter that contains two or more atoms.
What is an atom?
Atoms are the tiniest piece of matter. Matter is anything that takes up space.

Gather Materials

Steps to Create Your Own Ice Boat

STEP 1: Find one small stick per tupperware. If you are able to make more than one boat, I would advise it. Making more than one boat, especially in different sized containers, can serve your science investigation greatly.

STEP 2: Use tape to attach the stick vertically towards the back of what will become your boat.

STEP 3: Add about 3-5 drops of food coloring to the bottom of your tupperware.

STEP 4: Next, add water to about an inch from the top.

STEP 5: Put your soon to be ice boats in the freezer and wait. Depending on how large your ice boat is, 24-48 hours should be long enough for your liquid water to turn to solid ice.

STEP 6: 24-48 hours later… Before taking your almost ice boat out of the freezer, find a leaf that you can attach as your sail to the stick.

STEP 7: Attach your leaf to the stick. Be careful not to break your stick.

STEP 8: Your sail boat is complete. Observe what happened to the water and what your ice boat looks and feels like.

Engage your student with these Inquiry Questions:

What happened to the water when you put it in the freezer? Why?
Discuss how the liquid water turned to a solid. A liquid has more energy than a solid. Because of this, the atoms move slowly and are loosely arranged. That is why liquids will take the shape of any container. When it went into the freezer, it lost energy. This caused the atoms to cease their fluid movement and change to a solid. A solid has atoms that are (usually) tightly arranged with little energy.

When the water froze to ice, did it constrict or expand?
You can tell by looking at one of the above pictures that the water in the boats expanded as it changed to a solid. This is important to point out because this observation will come back later when learning the reason as to why ice floats on water.

*If you have a student that is older than 5th grade (middle school/high school), I would take the time to talk to them about the uniqueness of the water molecule when it reaches a temperature of freezing. Unlike other molecules, the water molecule does not constrict when energy decreases. On the contrary, something very different happens. In simple terms, the bonds of the atoms cause them to repel each other as opposed to pulling them closer together. Hence, the atoms spread apart causing the molecule to expand. This creates a greater volume with the same amount of mass. In turn, the density of the ice decreased.

Is the ice still water?
Yes. For younger students, understanding that ice is still water may be a hard thing for them to comprehend. Explain to them that the ice is still water, just in a different form. Water is the only substance that can change into all three forms of matter based on the transfer of energy.

As an analogy, I explain to my kids that I play different roles too, but am one person. I am mom to them, daughter to my parents, and wife to their dad. Just as I can be a mom, daughter, and wife, water can be liquid, ice, and water vapor. They may not understand fully, but this will help to build their background information, so that, when the time is right, their little brain can grasp the concept. It is similar to the trinity. Just as God is seen as the Father, Son, and Holy Spirit, water can take the form of a solid, liquid, or gas.

Set Your Ice Boat to Sail

STEP 9: Do not be scared to take your boat out of its container. If it doesn’t slip out of its container easily, rub the warmth of your hands under the bottom or dip it into the water without submersing it.

STEP 10: Set your ice boat to sail. Whether you have a pool, large tub of water, or even a bathtub, gently set your ice boat into the water. Observe and watch your boat. You may want to create a sort of whirlpool to give your boat some direction.

We sailed our boats in a round pool set up in our backyard. The boys were eager to have a boat race. This gave way to the children using their hands to create a whirlpool.

Slowly, the ice boats began to dissipate and we could visually see the food coloring streaking out into the pool water. It wasn’t long before our boats began to whither away and the weight of the sail caused them to tilt over into the water. The boats were eventually nothing more than a stick and a leaf.

Extend the learning with these Inquiry Questions:

Why did the ice boat float?
The easy answer is to say that the ice boat is less dense than the liquid water. Density is the amount of mass in its volume. Hence, the ice boat has less mass in its volume when compared to the liquid water. Ice is about 9% less dense than that of water. To really bring home the full answer, I would advise you to watch the video clips uploaded below, "Why does ice float?" It will be much more effective watching an explanation with visuals than reading about it from me. Smiley face.

Where did the boat go?
Simple answer... it melted. The process of melting is caused by an increase in energy to a solid. In this case, the energy from the liquid pool water transferred to the boat causing the solid ice to change to a liquid.
Why did some boats melt faster than others?
The larger boats were greater in size and volume (the amount of space something takes up), which required more energy to change their state. Thus, it took longer to melt the larger boats.

If intrigued... try this side lab involving evaporation

The process of liquid water changing into water vapor can take place very slowly or rather quickly depending on the conditions. To test this, you can easily put out a transparent cup of water. Make a marking on the cup to show the water level. Set the cup aside in a place out of the way. Come back to it a week later. Notice where the water level is compared to the original marking. Once again, wait another week. Recheck the water level. Continue to do this. During the process of evaporation, we may not visually see the atoms of the liquid water jumping up out of the pool into the air, but we can see the effects of the process through the decrease of water in its original container. *This can be related back to the Lord. We may not see God working in our life in day to day activities, but we can see how He takes care of us and protects us as we look out over the world.

Bring the lesson home for older students...

Remember when I told you to point out how the water in your ice boats expanded? Watch this video explaining how the 2 hydrogen atoms and the one oxygen atom in a molecule of water change physically when temperature drops to freezing. It will explain how the water molecule itself expands causing an increase in density due to the increase in volume. The video clip is short, but does an awesome job at explaining the chemistry behind this phenomenon!

Food for thought...

Looking for a more permanent science curriculum? Even though we pursue various science units that encompass labs and such, we also use a science textbook each year. Some might say that our science units supplement our textbook, while others would say the opposite to be true. The labs, experiments, graphic organizers, videos, and other activities bring the textbook information to life.

We use Abeka Science textbooks. I love that they incorporate God and His sovereignty into their curriculum. When I taught in the public school system, I noticed that many of my students were lacking in vocabulary. This made it difficult for them to understand the why behind many of our investigations. Unfortunately, they were deficient in their background knowledge. Our science time would be lacking too if it weren’t for the rich vocabulary and science language that we find in our science textbook and readers. If you are interested in shopping for a full-time science curriculum or even just a textbook to guide you, click on the following link! Happy homeschooling!

SHOP SCIENCE CURRICULUM