 Hi everyone, my name is Michael and I'm a librarian at the San Francisco Pike Library and for today's STEM challenge We're going to discover surface tension by dropping water on a penny But before we get started, do you know what STEM means? STEM is an acronym for science technology engineering and math so what makes drops on a penny a STEM challenge a Cohesion and surface tension play a role in this activity Cohesion is the traction of molecules of a substance that make them stick together for this case The molecules of water stick together surface tension is a special term that we use when There's cohesion between molecules that make the surface stronger and makes the drop bigger Before we get started, we're going to go over the materials So the materials I have here on the table is what you'll need for the challenge You would need a paper towel. You need some soap. You need a penny You need a cup of water and you would need a straw So let's get started. So first you would Take your paper towel and you place the paper towel on your table The next you will put the penny on the paper towel Next you would find your straw and then you would take the straw out of the wrapper Next you have your straw and you have your cup of water so go ahead and place the The straw into the cup of water and once you do that take your thumb and Place your thumb over the top of the straw and once you do that go ahead and Raise the straw and once you raise the straw you have some water in the in the straw Go ahead and release your thumb from the top and the water will drop out Go ahead and practice this a couple times until you get a hang of it and once you get a hang of it We're gonna move on to the next step. So the next step is gonna be very similar You're gonna be doing this as well. Go ahead place the straw into the cup then place your thumb over the top but now do not Release your thumb as quickly release your thumb very little so that little drops of water will drop from the straw Go ahead and practice this until you get a hang of it So you should have Little drops drop from the straw and once you get a hang of it. We could start the activity Okay, so now we're gonna start So go ahead place the straw into the cup of water place your Dumb over the top of the straw then we're gonna move the straw over to the penny And we're gonna see how many drops of water will stay on the penny before it kind of flows over so So once you go ahead and make a prediction of how many drops of water will stay on the penny before it flows over And we could kind of see if it kind of matches what you think after we do it So we'll start one Two three Four five Six Seven eight Nine So we successively dropped nine drops of water on a penny and it spilled over So was this your prediction was it higher than you predicted or was it lower than you predicted? Go ahead and wipe off your penny and try again So we're gonna try one more time So go ahead and place a straw in the cup of water and we're gonna start over again and see how many drops Will fit on the penny right now one two three four five six seven eight nine ten So we successfully put 10 drops of water onto penny before it spilled over Was this different from the first time you predicted? So next We're gonna try something different Go ahead and take a new piece of paper towel and place The towel onto your table and place the penny up top Now we're gonna be working with soap So we're gonna be placing soap into the cup of water And we're gonna see if there's a difference in the amount of drops you could place on a penny So go ahead and mix it up And we're gonna do the same process again So we're gonna be placing the straw into the cup of water Then place the finger over top of the straw And then we're gonna see how many drops of water will stay on a penny with soap in the water one two three four five six So there you can see we placed six drops onto the penny with soap And was this a little bit different than before? There are many factors that go into this The the height of the straw Matters as well too and the amount of water you drop onto the penny matters as well too So even if you count one drop there might be more water or less water So now you have just completed This the drops on a penny challenge. I want to thank you for joining us today If you are interested in the topics that we discussed like surface tension or water molecules You could go to your local library and ask the librarian for book recommendations And also be sure to check out our youtube channel for other STEM challenges as well too I want to thank you for joining us today, and I hope to see you guys soon