Science Outside the Square
Taking Science and enquiry that step further for Year 9 and 10 students
For those of you who love brainteasers…
This is one of the best interactive brainteaser sites I have seen in a long time. You will need a calculator. Click here to have a go.
Is it true that water spirals down a plughole in the opposite direction in the northern hemisphere?
The water in a sink or bath rotates one way as it drains in the northern hemisphere and the other way in the southern hemisphere. This is called the Coriolis effect, and it is caused by the rotation of the Earth. If you put a bathtub just to the north of the equator and another bathtub just to the south of the equator and drained them simultaneously, you would be able to see this happening.
Is this statement true? Well, Stanton Kindley (Y8, and currently attending school in England) decided to find out. This is what he did:
The Coriolis Force.
Aim: To see if water going down a drain is affected by the Coriolis force.
Hypothesis: I think that the water will be affected by the Coriolis force.
Method:
- Fill the sink with water then wait until the water has been stilled.
- Pull the plug and watch which way the water turns down the sink.
Problems:
- It was hard to distinguish which way the water was turning at first so I added shredded pieces of paper into the water.
- The water kept turning due to the angle that the water came from and the shape of the sink so I used the bath instead.
- Once again the water kept turning due to the irregular shape of the bath so I cut a bottle of lemonade in half because it was regular.
- Opening the bottle lid at the bottom made the water come out too fast so I cut a small hole in the lid to slow it’s down
- The paper when wet got stuck in the small hole so I used flour in the water instead.
Results:
|
Clockwise |
Anti-Clockwise |
Neither |
|
7 |
7 |
1 |
Surprisingly the results came to exactly half and half so I checked on the internet to ascertain my results and make my conclusion:
One can find both counter-clockwise and clockwise flowing drains in both hemispheres. Some people would like you to believe that the Coriolis force affects the flow of water down the drain in sinks, bathtubs, or toilet bowls. Don’t believe them! The Coriolis force is simply too weak to affect such small bodies of water.
Yes, Stanton is right. Water flows down a plughole the same way in the northern hemisphere as it does in the southern hemisphere. What can change the direction of flow, however, is the shape of the sink or bathtub. So, if you wanted to make money by demonstrating this mythical phenomenon to tourists at the equator, how would you go about it?
Stan suggests that you might be interested in this link on the Coriolis effect.
Many thanks to Stan for carrying out and sharing this excellent experiment and research with us. You’d be surprised how many people don’t know that this plughole story is a total myth!
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