Down the drain

Down the drain

Does where you are in the world affect water swirling around your plughole?

What you need:

  • A sink, preferably one with a plug on a chain
  • Water. How about using reusing the washing up water or bath water?
  • Pepper or talcum powder (optional)

How to:

  1. Make sure there's no hair or bits of dirt in the plughole. Fill the sink with water until it's at least 10cm deep. Let the water stand for 10-15 minutes or longer.
  2. Pull the plug out very gently, without putting your hand in.
  3. Note which way the water swirls down the plughole.
  4. Repeat the experiment. Can you try it in all the sinks in your house?

If it's hard to see which way the water swirls down the plughole, add a bit of pepper or talcum powder to the water.

What's going on?

It doesn't matter where you are in the world, the water could go either way down the plughole. Sometimes it doesn't swirl at all!

The rotation of the Earth does affect how liquids and gasses move. This effect is called the Coriolis effect. The Coriolis effect determines how currents move around the ocean and how the jet streams move around the Earth's atmosphere.

There isn't enough water in your sink to be affected by the Coriolis effect. If water always flows the same way down your plughole, it's more likely that something else is affecting it. Could it be how you pull the plug out? Or could it be where the tap is in the sink? How about where the plug is in the sink?

If you used a big enough bath, left the water for long enough to settle before pulling the plug out and made sure you pulled the plug out gently, you might notice a small effect from the Coriolis effect.