Submarine Action

School project • Easy hands-on science demo

Explore how real submarines dive and rise with this fun, hands-on school project! Using simple materials like plastic bottles, sand, and straws, kids can build a working model that demonstrates buoyancy and ballast control. Perfect for classroom demos, science fairs, or at-home experiments, this activity makes a complex science concept easy to understand and exciting to try.

Submarine model or submarine schematic — Model submarine showing buoyancy principle

How Submarines Dive - and How to Make a Model

Author: KidsGen Editorial Team | Published: 17 November 2012 | Updated: 17 November 2025

A submarine dives by making itself heavier; it surfaces by making itself lighter. This project shows the same idea using a simple model with side tanks that can be flooded and emptied. It's perfect for classroom demonstrations and science fairs.

Parts of a submarine

A modern submarine, such as this nuclear ballistic missile submarine, is almost as long as a football field - 100yd. It has an engine and propeller at the stern, and is operated by a crew of 140. Steam drives the turbines that turn the propeller. A submarine's hull is strong, but few submarines can go below 1,600ft.

Detailed labeled diagram of a submarine showing parts such as the propeller, nuclear reactor, missile tube, control room, torpedo room, sonar array, and crew quarters. — A labeled cutaway showing main parts of a submarine.

Make a Submarine - Step-by-step

STEP 1 - Prepare the main hull

Fill a large plastic bottle with sand using a funnel. Add sand until the bottle just sinks when tested in a tank of water - do small adjustments to find the correct amount.

STEP 2 - Make buoyancy tanks

Make a large hole in one side of two small plastic bottles. On the opposite side make a small hole big enough to insert a plastic straw.

STEP 3 - Attach the tanks

Attach the two small bottles to both sides of the large bottle using rubber bands. Twist so the small hole on each points upward.

STEP 4 - Insert straws & seal

Push a plastic straw into each small hole so a little protrudes. Seal the base with non-hardening modelling material to make a watertight joint.

STEP 5 - Add bulldog clips

Fit a small bulldog clip about halfway down each straw. The clip will squash the straw and stop the air being forced out by the surrounding water.

STEP 6 - Test and operate

Put your model in a tank of water. With the clips on it should float. Remove the clips to let water flood the tanks - the model will sink. To make it surface, blow slowly into both straws to force water out; once surfaced reapply clips to hold it floating.

STEP 7 - Make the Submarine Rise

To make the submarine surface again, blow slowly into both straws at once. The air will force the water out of the buoyancy tanks, and the submarine will rise to the surface.

STEP 8 - Keep the Submarine Afloat

When your model submarine has resurfaced, keep blowing slowly into the tanks. Replace each bulldog clip and your model submarine will remain floating on the surface.

You Will Need

Large plastic bottle
Sand (for ballast)
Plastic funnel
Tank or large container of water
Two small plastic bottles (for buoyancy tanks)

Bradawl, scissors, ruler
Two drinking straws, rubber bands
Non-hardening modelling material
Two small bulldog clips

Estimated time: ~30–60 minutes

What this shows

Buoyancy control: flooding and emptying side tanks changes overall weight - the same principle used by real submarines.

Tips & Safety

Adult supervision recommended when using tools (scissors, bradawl).
Check for leaks; seal joints well with non-hardening modelling clay or silicone if needed.
Use a clear tank so students can observe how water enters and leaves the tanks.

More School Projects