Museum at Home

Animal Athletes Challenge 4 | Freediving

Greatest Human Achievement

According to the Guinness World Records, the deepest human free-dive (holding breath) is 214 m by Herbert Nitsch from Austria in 2007.

Animal Competitor 1: Leatherback Turtle

Amazing ability

Known as the deepest diving reptile, Leatherback Turtles can dive down to 1230 m on one breath.

Built for deep (and long) diving

  • Large stores of oxygen in blood and muscles
  • Large collapsible lungs
  • Flexible shell to withstand pressure
  • Slow heart rate to conserve energy and oxygen
  • Can direct blood flow away from non-vital body organs

Where do they live?

In Australia, Leatherback Turtles live in both tropical and temperate waters. 

Animal Competitor 2: Beaked Whale

Amazing ability

The Cuvier Beaked Whale has been recorded as diving down to 3000m and staying down for 137.5 minutes. This is a world record for mammals. 

Built for deep (and long) diving

  • Large stores of oxygen stored in blood and muscles
  • Collapsible lungs
  • Slow heart rate
  • Streamlined body that helps it swim with less effort
  • Pockets for their flippers to reduce drag

Where do they live?

Beaked whales are found all over the world’s oceans, including on the Great Barrier Reef.

At Home Challenge

Fast fact: 'Freediving' is underwater diving that relies on holding your breath without scuba or snorkelling gear.

You will need:

What to do:

  • Practice making your diver dive then ascend by squeezing the bottle.
  • Put a mark on the outside of the bottle about half way down with the pen.
  • Try to control the diver so that it goes only as far as the mark.
  • Practice controlling the diver’s dive.
  • Start the clock timer and measure how many times you can get the diver down to the mark and back to the top in 10 seconds.
  • Record this result on your Challenge Sheet

What's happening?

When you squeeze the sides of the bottle, the air bubble in the top of the diver compresses (gets smaller). This forces water into the diver which makes it denser, making it sink. When you stop squeezing, the pressure on the air bubble reduces and the bubble expands. This pushes water out of the diver, making it less dense and it floats to the top of the bottle.

To make this activity into a scientific experiment you need to identify a variable:

  • Try using your other hand. Is this harder or easier?
  • Try changing the temperature of the water. Does this affect how fast the diver dives?
  • Try adding salt or sugar to the water. 

Video your results, post them online and tag #museumoftropicalqld #qldmuseum

At Home Activity

Make a Cartesian Diver

You will need:

  • 1.25 litre clear plastic bottle with lid 
  • Water
  • Food dye (optional)
  • 1 cup
  • 1 bendy straw or a pen cap
  • Paper clips
  • Scissors
  • Elastic band

What to do:

  • Bend the straw and cut it off so that the two ends are equal.
  • Wrap an elastic band around the ends (make sure you don’t crush the straw.)
  • Fill the cup with water.
  • Put the straw (Cartesian diver) in the cup and test that it floats.
  • Insert paper clips into the elastic until the diver floats vertically with the top just above the surface of the water.
  • Fill the bottle with water.
  • Colour the water with food dye.
  • Insert the diver into the bottle.
  • Top up the bottle with water until it is completely full.
  • Screw on the lid.
  • Squeeze the sides of the bottle. The diver should sink to the bottom of the bottle.
  • Let the bottle go and the diver should rise to the top of the bottle.


Fast fact: Some reef fish have a gas-filled organ, called a swim bladder, to control their buoyancy in the water. By adding or removing air from its swim bladder, the fish changes its density and moves up or down in the water.

Fast fact: Submarines can control their buoyancy by allowing water to enter and exit ballast tanks in the vessel. When water is pumped into a submarine’s ballast tank, its weight increases and it sinks. When it wants to rise, compressed air is pumped into the ballast tanks, which pushes out the water, decreasing its weight. 

Image credits: Alistair Rae, NOAA Image Library / Flickr