Have you ever seen a water droplet on a leaf? Have you seen little water skippers or other critters walk on water in a puddle or a pool? Have you ever wondered why water can seem to take on a spherical shape, or why some things can float or walk on water, without falling in? Water has some fascinating properties, both in its way to expand when frozen and in the ability of water molecules to cling tightly together in a bond of surface tension! Water molecules have a tendency to bond closely together, repelling away from other molecules (such as molecules found in the atmosphere). It’s because of these super tight bonds, that water appears to take on a sphere shape when a droplet falls on a leaf, or if you drop several drops on to a penny. The molecules pull together so tightly towards each other, and away from everything else, that they form a sort of “skin” or “bubble” on to each other!
This surface tension is also a key element in how plants get water and nutrients from the ground! This skin of water clings tightly to each other, even as the water droplets are pulled up the xylem of plants, inching along the stem until they reach the leaves and flower petals. Once they reach the leaves, they take the nutrients they’ve carried throughout the veins of the leaves to deposit nutritious minerals to the cells of the plant!
You can explore the properties of surface tension with some super fun experiments, that are easy to set up right in your home! The best part is, the key ingredient for these experiments is just water, so you’re sure to have the supplies on hand!
Find a Lens With A Drop Of Water!
Did you know that those little spheres of water droplets can actually magnify the objects on which they’re resting? Grab a nickel, a dime, and a quarter, and a small glass of water, and get ready to be amazed by the magnifying power of spheres and lenses!
A variety of coins
A medicine dropper (in a pinch, your finger will work as well)
A small cup of water
Flip your coins so that they are facing “heads up”. Then, take a medicine dropper and place 3 drops of water right on top of each other, over one part of your coin.
Try placing your drops on different places of your coin. A good place to magnify might be on the stamped date that the coin was minted with, or a phrase on the coin. You can also place it on a part of the image on the coin itself. Just choose one small area to magnify, and place your water on it!
Test this on a variety of coins, to see if you can magnify different areas of your coin!
Take it Further!
You can make this an experiment, by testing different variables with your water. Try using salt water, or water with a drop of dish soap in it. Will these variables change the way your water can collect into a spherical formation? Some substances will bond readily to water molecules, pulling them away from each other to connect to the substance. This may break the surface tension of the water, changing how it interacts with your coin!
Surface tension is the process by which water molecules will pull in towards each other, and down to the rest of the water molecules beneath the surface. When they do this, they’re also pulling away from other substances, like the air in the atmosphere around you. This curved water droplet can also bend light as it shines through! Just like any curved lens, when a light goes through the curved surface, it refracts and bends, which can magnify the image that’s on the other side of the lens! Thus, even a drop of water can act as a magnifying glass!
Another great way to play with surface tension, and perhaps have a few tricks up your sleeve at the same time, is with this super fun experiment!
Poking Holes and Plugging Leaks!
1-gallon Freezer bag
several sharpened pencils
Fill your bag until it is 3/4 filled with water. Seal it shut, leaving a small pocket of air inside.
Sharpen your pencils until the point is sharp to the touch. Sharpen about 5 or 6 pencils, and then set them aside.
One by one, pick up your pencils and stab them through your bag! Firmly press the point of the pencil into the bag, and keep pushing until it comes out on the other side.
Repeat this step with all of your pencils. Poke them through at different angles, and different distances.
How many pencils can you push through your bag until it starts leaking?
Have you ever made a batch of gooey slime? Slime is made up of a substance called polymers which is essentially a lot of tiny molecules linked together into strong and flexible chains! Many things in our lives consist of polymers, including the plastic bags you used in your experiment!
When you poked the sharp pencil through the bag, these polymer chains linked around the plastic, holding close to your pencil, creating a seal of polymer plastic around the pencil! There’s another force at play here too – the force of surface tension! The water molecules are heavily attracted to each other, pulling in tight together to pull away from air and other outside materials. When the seal was created by the polymers in the bag, the surface tension of the water also created a sort of film around itself, preventing the water from spilling out!
Take it Further!
The activities above are demonstrations, in that they demonstrate a known scientific effect in reality. To make these true experiments, try adding some variables! You can change the temperature of your water, or add variables like salt, oil, or diluted vinegar to see if these additives change the outcome of your experiments! You can also try using a variety of plastic bags in the Poking Holes and Plugging Leaks experiment. Will freezer bags work the same as regular sandwich bags? Do brands matter, or will dollar store bags work the same as brand name bags? Try your experiments, and if you do see changes in your results, repeat your experiments to see if you can find the cause of those changes!
Another way to experiment with these activities is to try to break the surface tension! Soap has a tendency to grab onto water molecules and pull them apart from their tendency to link together. If you make a lens with your water, and touch a Q-tip coated in soap to it, you might just find your lens breaking apart and spilling off the surface! Try this with your plastic bag experiment too. Will the water still form the same seals around the pencils if you add soap to the bag?
Follow the steps of the Scientific Method: Question, Research, Hypothesize, Test, Analyze, Draw Conclusions, and Communicate Your Results!