Drops on a Penny

Water is everywhere – we drink it, swim in it, use it to wash our cars and keep our plants alive. Because it’s such an essential part of our daily lives, sometimes we can take the amazing properties of water for granted. This week at Girlstart, students learned about one very cool characteristic of water: its surface tension! Week 3’s activity was based on the hydrologist career, which involves the movement of water in the Earth’s crust. Hydrologists use lots of models and computer simulations, but also spend time wading in lakes and rivers to collect samples.

For their activity, girls measured the number of drops that can fit on one penny. Before they began, girls made hypotheses based on the size of a penny: 1, 2, 3 drops? After running three trials, students were surprised to learn that the answer was closer to 20 drops!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The students conducted the same tests, this time using other liquids such as lime juice or vegetable oil. After observing the averages, students were able to see that the cohesion between H2O molecules creates incredibly strong surface tension!