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Get a Unique Perspective on Surface Tension With This Water Drop Experiment

 



Get a Unique Perspective on Surface Tension With This Water Drop Experiment



Water Drop Experiment
Water Drop 





Do you know what the surface of the water looks like? Well, what if you could change the way that surface looks? There’s actually a neat and simple experiment that you can do to make that happen, in your own home, using just some water and dish soap! This will allow you to get a unique perspective on surface tension—and maybe even figure out new ways to use it in your own projects! Let’s take a look at the experiment, then we’ll talk about how to do it at home with some useful tips from the video clip below.





What exactly is surface tension?



Surface tension is the elastic force that occurs between the molecules at the surface of liquids and solids. 



The water drop experiment has been around for centuries, but it's still fun to do! It's a simple experiment to demonstrate how surface tension works. All you need is an upside-down jar and water. Fill the jar with just enough water to cover the opening, turn it over, place your finger over the top (about halfway down), then release your finger quickly. As soon as you release your finger, see what happens. 



If nothing happens when you release your finger from its position in front of the jar opening: Congratulations! You've successfully demonstrated how surface tension works! When you lifted up your finger, the surface tension pulled up on the side closest to your finger and caused the liquid to form a drop. Gravity took care of the rest, making it fall back into the jar. 



If something happens when you release your finger from its position in front of the jar opening There are a few possible explanations for this happening. One is that there was too much water and not enough air so the surface tension couldn't pull up high enough to form the droplet. Another possibility is that there was too much air and not enough water so it never formed a drop because gravity didn't have anything to pull it into the jar.





How can I observe it?



  1. Fill up a container with water. 
  2. Get a large, round object like an orange or baseball and carefully place it at the edge of the water surface
  3. Slowly lower the ball into the water so that it is just barely touching the surface and watch what happens to the water as you submerge it more and more. As soon as the whole ball enters the water, it will break free from its contact with the table's surface tension and fall in completely. 



The experiment can also be done using some other objects such as a golf ball or grapefruit. You'll want to use something larger than a penny for this one though because the penny may not have enough weight to overcome the surface tension and will just keep floating instead of sinking. You may even need something bigger than a grapefruit if you're doing this one outside since the wind may push your object away from the water before it sinks in. Another thing you might notice when playing around with this experiment is that if you get the object too close to the surface without touching it, it will either float there indefinitely or start spinning on top of the water (a phenomenon called surface skidding). 


What's happening?: 


When we put an object into water, it must first create a connection between itself and the liquid.




Interesting things about surface tension




The first thing that we need to look at is the elasticity of the water. Elasticity refers to the ability of a material to return to its original shape after being stretched or bent. It turns out that water has very high elasticity, and can return to its original shape even after being pulled in opposite directions. That’s why we can fill up bottles with it without causing any damage because the water molecules are strong enough to resist the pressure from the air inside the bottle. 



In other words, if you pull one end of a balloon filled with water up and push down on the other end, it will not burst or leak because of surface tension. So, how do we demonstrate this? We can do so by creating a container with two sides – one end closed off, the other left open (we should use something like jars for this). Fill each jar with about 1/2 cup of water and put them close together on their side. Slowly bring the jars closer together until they touch. What happens? As soon as they touch, water droplets appear around their edges and start running down between them! Why does this happen?




Ideas for extension activities



Students can measure the height of the drop and guess its velocity by timing it with a stopwatch. They can calculate the height of the drop using this equation: h = 1⁄2 g t2, where h is the height and t is the time from drop to splash. 




Students can also predict how much higher or lower water will go when dropped from different heights. Students will need to use measurements for two heights, then compare those numbers to calculate how much higher or lower water will go at each height. To make predictions, students should ask themselves questions like how many times higher will the water go? or how many times lower? They can graph their data to visualize the answers. 



To explore more about surface tension, have your students study this great surface tension lesson plan!

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