Tag Archives: Surface tension

DIY: Fascinating Properties of Dihydrogen Monoxide

Humans are approximately 60% dihydrogen monoxide. If this is alarming, it might be helpful to know that this is just waterWhile water is certainly something quite familiar, it has a lot of properties that are very important and they all come from its famous chemical formula, H2O. Let’s take a look and try to understand a few.

Water molecules−which you can see an illustration of on the right−are made up of one Oxygen atom and two Hydrogen atoms. When atoms are bonded together, they do so because of electric charges. In this case, each hydrogen atom has one electron that it shares with the oxygen atom. Electrons carry a negative charge, and are held closer to the oxygen atom. This gives the oxygen atom a negative charge while leaving the hydrogen atom slightly positive. As you have almost certainly hear, opposites attract. These opposite charges pull on one another which keeps the water molecule together amidst a microscopic sea of atoms.

Due to this and the shape of the water molecule, each has a negative part where the oxygen is and a positive part where the hydrogen is. Scientists call molecules like this polar, and it is this polarity that gives rise to many of water’s unique and important properties!

The polar water molecules orient to one another and are held together by the electric attraction of opposite charges, which you can see in the illustration above.. This is important for us: If this were not the case, water would not be a liquid at room temperature at all! The relatively light water molecules would fly off as a gas because the molecules would have no attraction between them. Without this very important property, there would be no life as we know it. This attraction of water molecules to one another is called cohesion. They can also stick to many other objects by the same process, a property known as adhesion.

These two properties come together in the video above. The water molecules stick to the string, but also to one another. This allows the water to be poured at strange angles, and none of it would happen if it wasn’t for that fascinating little molecule, dihydrogen monoxide.

DIY Soap-Powered Boat

Ever filled a container with water, and then filled it some more? With a careful touch, you might have created a hill of liquid taller than the container itself. This works because of the surface tension, or cohesion, between water molecules. Place a small paper, plastic or cardboard “boat” on the water’s surface, and molecules will stick to it as well– that’s adhesion in action. Under normal conditions, adhesive forces on the boat pull it equally in all directions, so it doesn’t move on its own.

soapboat1

In this experiment, we use the chemical properties of soap to disturb the surface tension around the boat. Soap is made of polar molecules, which attract water. Introducing even a trace of detergent disturbs surface tension enough to unbalance the forces acting on a floating object. The boat appears to be propelled forward. In reality, the water behind it is no longer pulling against the water in front. The stronger pull ahead moves the boat forward!

soapboat2

This is a great project to try at home. All you need is a bowl of water, a small piece of paper or cardboard, (plastic bread bag tabs also work well), and liquid soap. Cutting a notch in the back of your boat can help to keep the soap where you want it. Dab a little soap onto the boat’s back edge with your finger, a toothpick, or a napkin, and watch your watercraft speed away!  Once surface tension has been chemically broken, adding more soap won’t cause a big enough difference to power your boat, so it’s a good idea to use a shallow pool of water and replace it each time you want to repeat the experiment.

Written By: Caela Barry

Paperclip Science!

Today is National Paperclip Day! Yes, even those simple bits of bent wire have their very own day. Being a science camp, we decided to celebrate in the only way that made sense: Paperclip science!

Lets start with a simple question. How can you tell if something will float? The most common and simple answer is density. Density measures how heavy something for a certain volume of it. It can be a little tricky to think about, so to make it simple, consider a two liter soda bottle. If we fill it with water, it will weigh two kilograms (about 4.4 pounds). Any substance that would make the bottle heavier than that will sink, and anything lighter will float. Paperclips are made of steel wire. If we filled the bottle with steel, it would weight a little north of 15 kilograms (or just over 34 pounds!). Paperclips should not float!

Density gif

These two metal spheres have the same mass, but very different volumes, resulting in very different densities. The larger one is hollow.

But we see them floating at the top of the water when carefully placed. As Eric mentioned in the video, this has to do with surface tension. We talked a fair amount about surface tension in our Teacher Appreciation Day post. For a more in depth discussion of this, check out that post here. In short, water molecules hold onto each other tightly. Its what pulls water into droplets, allows you to slightly overfill a glass of water, or pile drops of water on a penny.

pennygif

Water on a penny. The last drop is just too much for the surface tension to hold.

When the paperclip is carefully placed on the water, the surface tension bends and cradles it. The paperclip is still made out of steel, so it still should sink if you think about its density. However, there is another way to think about buoyancy. It’s called Archimedes’ Principle and has to do with displacement.

If you have a full bathtub, and then you get in it, the water will spill over the rim. This is displacement. When something goes into the water, it moves this water out of the way. The water doesn’t compress. Instead, it is lifted up. When you put something in the water, the force pushing up on it is the weight of the water that it pushed out of the way.

bounce

The less dense ball, when pushed underwater, displaces a mass of water greater than its own. Since buoyancy is stronger than gravity for this object, it is launched out into the air!

This fits perfectly with the density explanation as well. If we put the bottle of steel in the water from before, it will displace 2 kilograms of water, but weigh over 15 kilograms! As it weighs much more than the water it is displacing, it will sink.

Paperclip Float

However, the surface tension changes things for the paperclip. Above is a picture from beneath the floating paper clips. This is also how water striders walk on the water. The water bends, and displaces more water than the paperclip normally would.

WaterstriderEnWiki

A paper clip weighs about half of a gram. With the surface tension bending the water, it displaces more than half of a gram of water, allowing the paperclip to float, delicately, on the surface.

Soap is a surfactant. It greatly reduces the surface tension of the water. With the surface Note that another object like a ping pong ball would still float. It is held up by the fact that it is less dense than water, and does not require the aid of surface tension.

soapgif

This same phenomenon is what causes this to happen when soap is added to some milk and food coloring!

Milk-Soap Gif

DIY Project on Teacher Appreciation Day!

What a great holiday! Teachers are incredibly important in a child’s life, and their influence doesn’t stop when the school year ends. Their experiences, ideas, and memories will stay with their students for years to come. In addition, most kids decide whether or not they are interested in science or math at a very young age. As these STEM fields become more important than ever, this becomes a real issue.

At AstroCamp, we are science enthusiasts. This probably comes from the fact that we get to see awesome science demonstrations and experiment with amazing materials every day. However, we understand that this isn’t the background of every teacher. Trying to teach something that you aren’t familiar with can be a very tall task. As such, we wanted to give back with an easy but incredibly cool DIY science project!

One of the reasons this is a great demonstration is that the materials are easy to procure. All you need is a plate, dish soap, food coloring, whole milk, and a cotton swab.

Milk Soap 1

To perform the demonstration, simply pour some milk into the plate. Add food coloring drops on top. It doesn’t really matter where you put the food coloring so feel free to get creative!

Milk Soap 2Milk Soap 3

Once you are satisfied with your food coloring artistry, add a bit of soap to the cotton swab. Simply dip it into the milk. Enjoy!

Milk Soap 4

Wow! One of the other great things about this demonstration is that it can be used to teach more than one thing! For younger kids, you can add certain colors and use it as an experiment where the goal is to learn about how colors mix together.

For more advanced or older students, it can be used to illustrate quite a bit. It all starts with something called “surface tension”. Water molecules (H2O) are highly polar, meaning one side is positively charged, while the other is more negative. These opposite charges attract. The oxygen parts of one molecule will be attracted to the hydrogen portions of nearby water molecules creating a tightly attracted tangled mess.

Inside the water, this pull occurs in all directions. At the surface, the water is pulled down, as it is not attracted to the air in the same way. This attraction causes the surface to hold together. With small amounts of water, this is what causes droplets to form. However, if some other molecules get in the way of this attraction, the surface tension will change.

Milk is mostly water with some dissolved fat molecules and other stuff in it. Soap molecules have two parts: A polar head that interacts nicely with water, and a hydrocarbon tail that doesn’t get along with water at all! When the soap is introduced, it quickly begins to surround the fat molecules in the milk. This disrupts the surface tension in the center of the plate, leading to the rest of the surface being pulled away by the remaining surface tension further from the soap.

Milk-Soap Gif

It all happens very quickly, but can be re-initiated by adding another bit of soap! After enough soap is added, all of the fat will be surrounded by soap, and the surface tension will be irreparably changed. At this point, adding soap won’t do anything further.

At this point, this fun activity is a great teaching tool and demonstration. To make the activity more inquisitive and experimental, feel free to try doing it with other liquids (water, half-and-half, different kinds of milk, juice, coffee etc.) or other kinds of soap and see how the results change!

 

 

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