This experiment investigated the surface tension of water on top of a dry penny vs. a penny coated in dishwasher soap.

In order to study the problem, 4 dry pennies and 4 pennies coated in dishwasher soap were placed on top of paper towels and an eyedropper was used to pour drops of water onto the pennies.  The number of water drops that both the dry and soap pennies sustained were recorded and the averages were compared.

Results showed that pennies coated in dishwasher soap held much fewer drops of water and that on average, dry pennies held over 5 times the number of drops that soap-covered pennies did.

This proved that the hypothesis that “if the pennies are covered in soap, then the surface tension will be much weaker” was supported because the water and soap molecules do not attract each other, therefore creating a weaker surface tension and an unstable pool of liquid. Other groups’ experiments showed similar results, with dry pennies sustaining a drastically higher number of water drops. Despite the similar results, however, there were gaps of differences between the averages of all groups. Possible reasons for these gaps include who and where on the penny the water was poured onto and the amount of soap used to coat the pennies.

To extend this experiment, different types of soaps, oils, and liquids can be tested and swapped in with the dishwasher soap. Different types of coin and surfaces may also help reach a more accurate conclusion and extend the experiment.

Finally, if the experiment was repeated, some changes to improve the experimental design could be using a larger sample size of pennies and staying more consistent with the amount of soap coating.


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