Science Buddies: "Ask an Expert"

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I am doing this project and planned to add milliliters of soap to water to show how soap decreases the surface tension. However, when I add the tiniest bit of soap the needle immediately sinks, so I'm not able to calculate the surface tension. What do I do now?

Hi DiligentWorker,

From your description it seems that the needle may not be balanced properly. Can you adjust the balance so that the needle rests on the surface of the soapy water? If so, you might try the surface tension measurement for the soapy water. But the results won’t be comparable to your previous test for plain water because you adjusted the balance. So you should repeat the plain water test with the same balance point used for the soapy water.

I hope this helps. Please post again if you have more questions.

A. Norman