How to Build a Submarine STEM Activity for Kids

Table of Contents

1. Introduction
2. The Core Science: Density and Buoyancy
3. How Real Submarines Work: The Magic of Ballast
4. Materials Needed for Your Submarine Build
5. Step-by-Step Instructions: Building Your Submarine
6. Troubleshooting and the Scientific Method
7. Connecting STEM to the Kitchen
8. Advanced Concepts for Older Children
9. Why Hands-On STEM Matters
10. Structuring the Activity for a Classroom or Group
11. Environmental Connection: Marine Engineering and the Ocean
12. Tips for Success with Different Age Groups
13. Conclusion
14. FAQ

Introduction

Watching a child discover that they can control whether an object sinks or floats is a powerful moment in early science education. It starts in the bathtub or the kitchen sink, where heavy spoons drop to the bottom while plastic cups bob on the surface. Moving from that basic observation to understanding the complex mechanics of a deep-sea vessel is what makes a build a submarine STEM activity so rewarding for both parents and educators. It transforms a simple afternoon at home into a deep dive into physics, engineering, and the wonders of the ocean.

At I’m the Chef Too!, we believe that the best way to learn is by doing, especially when that "doing" involves materials you can find right in your pantry or recycling bin. If you want to keep that hands-on momentum going, join The Chef's Club for a new STEM cooking adventure every month.

This guide provides everything you need to lead a successful submarine build, from the scientific "why" to the step-by-step "how." Whether you are a parent looking for a rainy-day project or a teacher planning a unit on fluid dynamics, these instructions are designed to make the experience educational and genuinely fun. If you are looking for more hands-on ideas beyond this project, browse our full kit collection for your next family activity.

Quick Answer: To build a basic STEM submarine, use a plastic bottle weighted with pennies to achieve neutral buoyancy. By adding a rubber band-powered propeller and adjusting the amount of air and water inside the bottle (ballast), children can control how the vessel moves and floats.

The Core Science: Density and Buoyancy

Before we pick up a pair of scissors or a bottle of glue, it is essential to understand the "magic" behind why things float. For a child, a heavy metal ship floating on the ocean seems to defy logic. To explain this, we have to look at two major concepts: density and buoyancy.

Understanding Density

Density is a measure of how much "stuff" is packed into a certain amount of space. In scientific terms, it is mass divided by volume. We can explain this to children by using a kitchen analogy. If you have a cup of popcorn and a cup of sugar, the cup of sugar is much heavier even though they take up the same amount of space. The sugar is more dense.

In the water, density determines what sinks and what floats. If an object is denser than the water it is in, it will sink. If it is less dense, it will float. When we build our submarine, we are essentially building a machine that allows us to change its density on command. For a kid-friendly follow-up on this concept, try our buoyancy experiment guide.

Archimedes and the Power of Buoyancy

Buoyancy is the upward force that a fluid exerts on an object. Thousands of years ago, a scientist named Archimedes discovered that the buoyant force on an object is equal to the weight of the fluid that the object displaces. This is known as Archimedes' Principle.

When we place our plastic bottle submarine in a tub of water, the bottle pushes some water out of the way to make room for itself. This is called displacement. If the water that was pushed away weighs more than the bottle itself, the water will push back up with enough force to keep the bottle afloat. This is called positive buoyancy. If the bottle is heavier than the displaced water, it has negative buoyancy and sinks.

Key Takeaway: Submarines move vertically in the water by changing their overall density, allowing them to switch between positive, negative, and neutral buoyancy.

How Real Submarines Work: The Magic of Ballast

A real submarine is a marvel of engineering because it can stay perfectly still in the middle of the water column—neither sinking nor floating. This state is called neutral buoyancy. To achieve this, submarines use something called ballast tanks.

The Air-Water Exchange
Ballast tanks are large compartments located between the inner and outer hulls of a submarine. When the submarine is on the surface, these tanks are filled with air, making the vessel less dense than the surrounding water. When it is time to dive, the crew opens "flood holes" at the bottom of the tanks and "vent valves" at the top. The air escapes out the top, and sea water rushes in the bottom.

As the tanks fill with water, the submarine becomes heavier and its density increases. Once the submarine reaches its desired depth, the vents are closed. To rise back to the surface, the crew uses compressed air to blow the water back out of the tanks. This makes the submarine lighter and less dense than the water again, causing it to float upward.

Engineering in Miniature
In our build a submarine STEM activity, we recreate this process. Instead of complex pumps and compressed air, we use the weight of pennies and the manual addition of water to the bottle. This allows children to see exactly how the ratio of air to water affects the vessel’s behavior in real-time. If your learner enjoys kitchen science projects that show how density works in everyday life, this liquid density experiment is a great companion activity.

Materials Needed for Your Submarine Build

To make this activity accessible and low-stress, we focus on common household items. Using recycled materials also teaches children about sustainability and creative problem-solving.

• Small Plastic Bottle: A 16oz or 20oz water or soda bottle works best. Ensure it has a tight-sealing cap.
• Weights: Pennies are perfect because they are uniform in size and weight. You will need about 10–15.
• Adhesive: A hot glue gun (with adult supervision) or waterproof duct tape.
• Propulsion: Two or three large rubber bands, a popsicle stick, and a piece of stiff plastic (like a yogurt container lid) to create a propeller.
• Tools: A push pin, scissors, and a pair of pliers (for bending paper clips).
• The Hull Connector: A large paper clip or a piece of sturdy wire.
• A Large Container: A bathtub, a clear plastic storage bin, or a deep sink filled with water.

Step-by-Step Instructions: Building Your Submarine

Building the submarine is an exercise in fine motor skills and following a logical sequence. Encourage your child to predict what will happen at each stage of the construction.

Step 1: Preparing the Hull

The bottle serves as the main body, or hull, of our submarine. To allow water to enter and exit (acting as our ballast tank), we need to create an opening.

What to do: Carefully cut a small rectangular hole (about 1 inch by 2 inches) in the side of the bottle. This will be the "bottom" of your submarine. This hole allows water to flow into the bottle. Across from this hole, on the "top" of the submarine, use a push pin to poke two or three small air vent holes. These vents allow air to escape so water can get in.

Step 2: Adding the Ballast

A plastic bottle full of air will simply float on the surface. We need to add weight to the bottom to ensure the submarine stays upright and has the potential to sink.

What to do: Glue or tape pennies to a popsicle stick. Then, secure the popsicle stick to the bottom of the bottle, right next to the large hole you cut earlier. The goal is to add enough weight so that the bottle sits low in the water but does not immediately plummet to the bottom.

Step 3: Creating the Propeller

Propulsion is what moves our submarine forward. We will build a simple "twisted-motor" propeller using the energy stored in a rubber band.

What to do:

1. Cut a small propeller shape out of a sturdy plastic lid (like a yogurt or margarine tub lid). It should look like two small blades joined in the center.
2. Use a push pin to make a hole in the center of the propeller and another hole in the center of the bottle cap.
3. Straighten a paper clip, leaving a small hook at one end. Thread it through the propeller and then through the bottle cap.
4. Bend the wire on the outside of the cap to lock the propeller in place. On the inside of the cap, you should have a hook.

Step 4: Connecting the Motor

Now we need to provide the power. Rubber bands are excellent for demonstrating potential and kinetic energy.

What to do: Hook one end of your rubber bands onto the paper clip hook inside the bottle cap. To secure the other end, poke a small hole in the very bottom of the bottle and use another paper clip to create an internal hook. Stretch the rubber bands from the cap hook to the bottom hook. Screw the cap onto the bottle.

Step 5: The Test Launch

Now comes the most exciting part: the sea trials. Fill your basin or tub with water and prepare to observe.

What to do: Wind the propeller repeatedly to twist the rubber bands. This stores potential energy. Place the submarine in the water. As the rubber band untwists, the propeller spins, pushing water backward and moving the submarine forward.

Bottom line: The success of the submarine depends on the balance between the weight of the pennies and the volume of air trapped inside the bottle. If it sinks too fast, remove a penny. If it won't go under, add one.

Troubleshooting and the Scientific Method

Science is rarely perfect on the first try. When a submarine build doesn't go exactly as planned, it provides a perfect opportunity to teach the scientific method. Instead of seeing a "failure," frame it as a "data point."

Issue: The submarine keeps flipping upside down.

• The Fix: This usually means the center of gravity is too high. Make sure your penny-weighted popsicle stick is exactly at the bottom of the bottle. You may need to add more weight to the bottom to counteract the buoyancy of the air at the top.

Issue: The submarine stays on the surface and won't dive.

• The Fix: Check your air vents. If air cannot escape the top of the bottle, water cannot enter the bottom. Make the vent holes slightly larger or add one more. Alternatively, you may need more ballast (pennies).

Issue: The propeller spins, but the sub doesn't move.

• The Fix: Look at the angle of your propeller blades. If they are completely flat, they won't push much water. Gently twist or bend the blades so they are at a slight angle. This allows them to "bite" into the water and create thrust.

The Scientific Method in Action:

1. Observe: The submarine is tilting to the left.
2. Hypothesize: I think the pennies are not centered.
3. Experiment: Move the pennies to the right.
4. Analyze: Did it stay level this time?

Connecting STEM to the Kitchen

At I'm the Chef Too!, we love finding the science in everyday life, and the kitchen is actually a fantastic place to explore the very same concepts used in submarine engineering. Many of the physical properties we see in fluids apply to both the ocean and the mixing bowl.

Liquid Density and Layering

Just as a submarine moves through different levels of water density, we can see density in action by layering different liquids. You can conduct a "Kitchen Density Column" experiment using honey, dish soap, water, and vegetable oil. Because each liquid has a different mass per volume, they will stack on top of each other rather than mixing immediately. This is a visual representation of why some things float while others sink.

Displacement in Measuring

When we teach kids to cook, we often use the displacement method to measure irregular solids. If a recipe calls for half a cup of butter, and the butter is in a weirdly shaped chunk, you can fill a measuring cup with one cup of water and add the butter until the water level reaches 1.5 cups. The butter "pushed aside" exactly half a cup of water. This is the exact same principle Archimedes used to solve the problem of the King's crown!

Aeration and Buoyancy in Baking

In baking, we often try to "trap" air to make things light and fluffy. When we whip egg whites or cream, we are folding air into the liquid. This reduces the density of the mixture. Think of a pancake batter. A thick, heavy batter might stay at the bottom of a bowl, but once we add leavening agents like baking powder, bubbles form. This "ballast of air" makes the pancakes rise and become fluffy.

We explore these concepts in depth through our various themed adventures. For example, when children create our Galaxy Donut Kit, they are working with glazes and textures that require an understanding of how different ingredients interact. Or, when building Erupting Volcano Cakes Kit, they see the chemical reaction between an acid and a base—another form of gas production that can create movement and pressure, much like the air used in a submarine’s ballast tanks.

Advanced Concepts for Older Children

If you are working with middle-school-aged children or advanced students, you can take the build a submarine STEM activity a step further by introducing more complex physics.

Newton’s Third Law of Motion

The propulsion system of the submarine is a classic example of Newton's Third Law: For every action, there is an equal and opposite reaction. As the propeller blades spin, they push the water backward (the action). The water, in turn, pushes the propeller and the submarine forward (the reaction). You can experiment with different propeller shapes—larger blades, more blades, or steeper angles—to see which produces the most "reaction" and makes the sub travel faster.

Hydrostatic Pressure

As a submarine goes deeper into the ocean, the weight of the water above it increases. This is called hydrostatic pressure. For every 33 feet of depth, the pressure increases by one atmosphere (about 14.7 pounds per square inch). While our plastic bottle sub won't go deep enough to feel this, you can discuss why real submarines are shaped like cylinders or spheres. These shapes distribute the immense pressure of the deep ocean evenly across the hull, preventing it from collapsing.

The Role of Fins and Control Surfaces

In addition to the propeller, real submarines use "diving planes" or fins to help them angle up or down. You can add small cardboard or plastic fins to the sides of your bottle. By tilting these fins, you can influence whether your submarine dives steeply or glides gradually. This introduces the concept of hydrodynamics—the study of how liquids move around solid objects.

Why Hands-On STEM Matters

In a world where children are often surrounded by screens and passive entertainment, hands-on activities like building a submarine provide a much-needed antidote. These projects require patience, manual dexterity, and critical thinking.

Building Confidence
There is a unique sense of pride that comes from creating something that actually works. When a child sees their submarine submerge and then resurface on command, they aren't just learning about buoyancy; they are learning that they can solve problems and build machines. This builds "creative confidence," the belief that they have the power to change the world around them through engineering and art.

Encouraging Multi-Disciplinary Thinking
STEM (Science, Technology, Engineering, and Math) is most effective when it is integrated. This activity isn't just a science lesson; it’s an engineering challenge that requires measurement (math) and often a bit of artistic flair in the design of the vessel. We often see that when children are allowed to decorate their submarines or give them names, they become more emotionally invested in the success of the project.

Screen-Free Family Bonding
One of our primary goals at I'm the Chef Too! is to create joyful family memories away from digital devices. Building a submarine is a collaborative effort. It’s an opportunity for a parent and child to sit together on the floor, troubleshoot a stubborn rubber band, and cheer when the sub finally makes its way across the bathtub. These moments of shared discovery are where the real "edutainment" happens.

Structuring the Activity for a Classroom or Group

If you are an educator or a homeschool co-op leader, this activity can be easily adapted for a group setting. Here is a suggested structure for a 60-minute lesson:

1. The Hook (5 minutes): Show a video of a real submarine diving or show a picture of a heavy ship and ask the students, "Why doesn't this sink?"
2. The Demonstration (10 minutes): Use a clear tank of water to show how an empty sealed bottle floats and a bottle filled with water sinks. Introduce the term "ballast."
3. The Build (30 minutes): Let students work in pairs to construct their submarines. Providing pre-cut bottle openings can save time and ensure safety for younger groups.
4. The Competition (10 minutes): Hold a "Neutral Buoyancy Challenge." The student who can get their submarine to hover in the middle of the tank for the longest time wins.
5. Wrap-Up (5 minutes): Ask students to share one thing they would change about their design to make it go faster or dive better.

If you're planning this as a classroom lesson, homeschool co-op project, or group challenge, our school and group programmes can help bring hands-on STEM to more learners.

Key Takeaway: Collaboration in STEM activities mimics real-world engineering teams, where diverse perspectives lead to better problem-solving and innovation.

Environmental Connection: Marine Engineering and the Ocean

Beyond the physics, building a submarine is a great gateway to talking about oceanography and environmental science. Submarines and Remotely Operated Vehicles (ROVs) are essential tools for scientists studying the effects of climate change on our oceans.

Exploring the Unknown
Most of our ocean remains unexplored. We know more about the surface of the moon than we do about the deepest parts of our own planet. Submarines allow us to see bioluminescent creatures, underwater volcanoes, and the hidden landscapes of the abyss. This can spark a child's interest in marine biology or environmental conservation.

The Future of Engineering
The engineers of tomorrow will need to design vessels that are more efficient and less impactful on marine life. By starting with a simple plastic bottle today, a child might eventually go on to design the next generation of eco-friendly submersibles. We want to nurture that spark of curiosity and show them that science is not just a subject in a book—it is a tool for exploration. For more ocean-themed inspiration, explore our ocean STEM activities.

Tips for Success with Different Age Groups

While the basic submarine build is versatile, you can tailor the experience to the developmental stage of the child.

For Younger Children (Ages 5-7):

• Focus on the "Sink or Float" aspect.
• Do the heavy cutting and hot gluing for them.
• Let them choose the colors for the "fins" and help drop the pennies in.
• Keep the explanation simple: "Air makes it stay up, water and pennies make it go down."

For Elementary Students (Ages 8-11):

• Let them handle the construction, including the propeller assembly.
• Introduce the concept of displacement and have them guess how many pennies it will take to make the bottle sink.
• Encourage them to decorate their sub to look like a real naval vessel or a research sub.

For Middle Schoolers (Ages 12+):

• Challenge them to create a "dual-tank" system using two bottles.
• Have them calculate the volume of the bottle and predict the exact weight needed for neutral buoyancy.
• Incorporate a timer to measure the speed of the submarine and have them graph the results of different propeller designs.

Conclusion

The build a submarine STEM activity is more than just a craft project; it is a gateway to understanding the physical laws that govern our world. By using simple materials like plastic bottles and rubber bands, children gain a deep, intuitive grasp of density, buoyancy, and mechanical engineering. They learn that science isn't a collection of static facts, but a dynamic process of questioning, building, and testing.

At I'm the Chef Too!, our mission is to make this kind of hands-on learning accessible and delicious. Whether you are exploring the depths of the ocean with a homemade sub or exploring the chemistry of a kitchen with one of our kits, the goal is the same: to spark curiosity and build confidence through "edutainment." We believe that when you blend STEM with the arts and hands-on experiences, you create a recipe for lifelong learning.

• Gather your materials and start with a simple "sink or float" test.
• Focus on the balance between air and ballast to find that perfect "neutral" hover.
• Don't be afraid of mistakes—they are just part of the engineering process.

"The best way to predict the future is to create it, one experiment at a time."

For more ways to bring STEM to life at home, join The Chef's Club. Our monthly subscription delivers a new cooking STEM adventure to your door, perfectly blending food, science, and the arts into an experience the whole family will love.

FAQ

What is the most important part of making the submarine dive?

The most important part is the balance of "ballast," which is the weight added to the bottle. You must have holes that allow air to escape from the top so that water can enter the bottom; without this air-water exchange, the submarine will remain too light to submerge. If you want another kid-friendly way to explore the same idea, this buoyancy experiment guide is a helpful next step.

Can I build this submarine without a hot glue gun?

Yes, you can use waterproof duct tape or a strong waterproof adhesive like silicone sealant. The key is ensuring that whatever you use to attach the weights and propeller can withstand being submerged in water without losing its grip.

Why do we need a rubber band for the submarine?

The rubber band serves as the "engine" of the submarine by storing potential energy when you wind it up. When released, it converts that stored energy into kinetic energy, spinning the propeller and creating the thrust needed to move the vessel through the water.

How do I make the submarine stay in the middle of the water?

This is called achieving neutral buoyancy. You can reach this state by carefully adding or removing small weights (like pennies) or by adjusting the amount of water trapped inside the bottle until the submarine's density perfectly matches the density of the water around it. For more ocean-themed hands-on learning, these ocean STEM activities for kids are a great match.