You'll need

  • A waterproof marker pen
  • A bar magnet, with the north and south poles marked
  • A water balloon
  • A large container of water (big enough to hold the balloon)
  • Sticky tape
  • A compass (you can use the one on a smartphone)

What to do

  1. Blow up the water balloon and tie a knot to hold the air in. Hold the balloon with the knot at the bottom.
  2. Using the waterproof marker pen, draw a straight line across the round top of the blown-up balloon.
  3. Hold the bar magnet against the side of the balloon so the north pole of the magnet lines up with the line you have drawn.
  4. Use sticky tape to attach the bar magnet firmly to the balloon. To make sure the magnet doesn’t fall off, you might need to use lots of tape.
  5. Place the balloon in the middle of the bucket of water and watch what happens.
  6. Use a compass to check whether the balloon compass is pointing north. If you are using a smartphone compass, make sure it is not in a magnetic case (also, be careful not to drop it in the water, SPLASH!).

Questions to ask

Did the balloon move when you placed it in the water? Did it move in a straight line, or did it turn like a wheel? Try again, but place the balloon with the line pointing in a different direction.

When you checked with your compass, did the balloon point north?

What's happening

Earth is a giant magnet. The North Pole (the top of Earth on most maps) and the South Pole (the bottom of Earth) are the magnetic poles. A compass points toward the magnetic North Pole. The magnetic poles don’t match the geographic poles. (The geographic poles are the ones that Earth spins around.) The magnetic north pole is about 400 km from the geographical North Pole. And it moves about 50 km every year! The difference between the magnetic north pole and the geographical North Pole is called the magnetic declination.

All magnets have a north and a south pole. If you allow a bar magnet to move freely by suspending it on a light piece of string or by floating it in water, it will move to align with Earth’s magnetic field. The magnet’s north pole will point to Earth’s magnetic North Pole. The magnet’s south pole will point to Earth’s magnetic South Pole.

Did you know

Animals use Earth’s magnetic field to help them navigate around the world. Young loggerhead turtles that have never migrated before can navigate across an entire ocean to return to the beach where they were born. Their journey can take up to 16 years, travelling from Queensland as far as South America and back. The turtles complete this amazing journey by using Earth’s magnetic field to guide them home.

(Sound of bubbles popping).

Tim: Hi everyone, my name’s Tim and I’m from the Questacon Science Squad. I’m going to show you how to make a balloon compass.

To do this you need a container filled with water, just like this one here.

(Camera zooms into Tim showing the container of water)

You also need to have a bar magnet.

(Tim picks up the bar magnet)

You need to have a water-proof marker, just like this one here

(Tim picks up the marker and takes the lids off and then pops it back on again)

You need to have some sticky tape

(Tim picks up the sticky tape)

You need to have a balloon pump to blow up your balloon because my lungs are a little bit weak.

(Tim picks up the pump)

And you also need to have the almighty water balloon, you have here.

(Tim picks up the water balloon)

So the first step is to take this water balloon and the balloon pump and to pump it up about the same size as you would fill it if you were filling it with water.

(Tim picks up the pump and balloon then puts the balloon over the end of the pump and pumps the balloon up)

So once you got it to this size just tie it off.

(Tim ties off the balloon)

And now, take your water-proof marker and mark along the fat edge of the balloon. Mark a straight line, like this.

(Tim picks up the marker and draws a line on the balloon then places the marker back on the table)

Once you’ve done that, take the bar magnet and look for the North Pole, you can see there it says “N” on it.

(Tim picks up the magnet and shows the N on it)

So line up the North Pole with that straight line, take some of the tape I have over here and tape that onto the balloon at one end, and tape it onto the other end as well.

(Tim places the magnet on the balloon and then gets some tape and places it on each end to stick magnet on)

And now your balloon compass is ready to go. So all you need to do is put that into the water.

(Tim places balloon compass into the water)

And you can see that your balloon compass spins around until it points in a certain direction.

(The balloon spins in the water then stops)

(Camera zooms back into Tim)

Now if you want to find out what direction that balloon compass is pointing and why it’s doing that, head to the Questacon Science Squad website. Catch you next time.