This fun science activity gets to the root of how submarines work!

Real submarines fill their ballast tanks with air to surface, and vent the air to sink. This simple experiment uses items found in most kitchens to show how buoyancy and ballast works (plus, it's just alot of fun to do with kids!)

Suitable for ages:
2 years and up
Time required:
30 mins
2 out of 5
Related Exhibition: HMAS Onslow

Materials needed to make a carrot submarine

What you’ll need:

  • 1 carrot – fairly straight, not too tapered (If you don’t have a carrot; cut down a potato)
  • Baking powder (not baking soda)
  • Toothpicks
  • Deep bowl or pot of water

To Make: 

Step 1:
Slice the carrot in half lengthwise, to create a long flat base, and trim the ends so it’s an evenish shape.

Sliced carrot

Step 2:
Make a hole in the middle of the base that is fairly deep but doesn’t go right through.

Making a hole in the carrot submarine

Step 3.
Cut two toothpicks in half and stick two bits at each end of the top of the carrot (the side without the hole).

Putting toothpicks in the carrot submarine

Step 4:
Pack the hole with baking powder – be sure to press it in firmly.

Putting baking powder in the carrot submarine

Step 5:
Set your submarine in the bottom of the water container and watch what happens.

Carrot submarine in the water

Step 6:
If your submarine is unstable, try re-positioning the toothpicks until it’s balanced.

Carrot submarine floating

What’s going on (the science-y bit):

Carrots naturally sink in water. The toothpicks give your carrot some extra buoyancy, so it doesn’t sink so quickly.

When the baking powder gets wet, it reacts with the water to form bubbles of carbon dioxide gas. The bubbles build up under the submarine and push it to the surface.

When it reaches the top, the bubbles escape and the submarine sinks again. The cycle repeats with the submarine diving and surfacing until all the baking powder has reacted.


See the inner workings of a real submarine - get behind the wheel and peer through the periscope of HMAS Onslow here at the museum! 

We’d love to see your creations! 

Please send us photos either by email to: or tag us on Instagram - just tag the photo with our username

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