Capillary Action Definition for Kids

Capillary Action Definition for Kids


We all know that blood is the most important liquid that we have inside of our bodies. Our blood is responsible for bringing different cells to different organs, for bringing nutrients from one place to another, and for many other jobs. It’s interesting to think about how there can be blood in our feet all of the way up to our heads, but what makes the blood stay in the higher parts of our body? Much like a glass of water, you would think that all of your blood would fall to your feet because of a unique environmental element known as gravity. Luckily, our bodies have a very special task known as capillary action to help get blood everywhere that it needs to go.

How Blood Moves

Our blood moves in many different ways but the most important way is by circulating through our entire system. It goes all the way down our body and then all the way up to the top and this is all because of capillaries. You can think of capillaries as little sponges that we have all over the place that help to absorb blood and bring it everywhere that we need It to go. Imagine putting a sponge on a wet surface and watching the water get absorbed. Instead of just staying in the bottom of the sponge, the water actually makes its way to the top of the sponge.

Who Has Capillaries?

Relatively every species on the planet has capillaries because every species needs a lot of blood to be circulated through its system. Plants even have capillaries that don’t transport blood, but bring water throughout their stems. All of the water that they get helps to nourish the stems and leaves to help the plant grow healthily.

Another Name for Capillary Action

If you are a fan of sports you might have heard the term “wicking” when you take a look at the high performance clothing that athletes wear. The purpose of these materials is to help draw sweat off of your body and absorb it into the material so you body can feel more comfortable and cooler while you’re playing sports outside or if you’re working out in the gym. Much like capillary action, high performance clothing draws liquid upwards instead of pushing it back against your body.

Understanding Cohesion and Adhesion

There are 2 main components to the idea of capillary action: cohesion and adhesion and they each help to attract molecules, but in different ways. With cohesion 2 molecules that are related will be attracted to each other whereas with adhesion, 2 completely different molecules are attracted to each other. As an example, 1 water molecule + 1 glass molecule = adhesion and 1 water molecule + 1 water molecule = cohesion.

When you find that the attraction between adhesive molecules is stronger than the attraction between cohesive molecules, capillary action will begin to happen.

The Importance of Capillary Action

Not only is it important that blood gets to every organ in your body but it also helps to make sure that your body is properly nourished. This is a property that is the same in humans and animals as it is in plants. With blood, it brings proteins and healthy sugars throughout your body when in plants; it brings water and nutrients throughout the plant. Without capillary action, you wouldn’t have the ability to stay strong and healthy, as your body wouldn’t have the opportunity to absorb important nutrients.

How to Test Capillary Action

If you’re interested in seeing how capillary action works inside of your body and inside of plants, consider this unique experiment that you can do entirely at home.

What You’ll Need:

  • 1 see-through plastic or glass cup
  • 10 drops of red food coloring
  • 1 stalk of pale green celery
  • 1 pair of scissors


Step 1: Fill your glass or plastic cup with ¼ cup of water
Step 2: Add 10 red food coloring drops to the water and stir it thoroughly
Step 3: Grab your piece of pale green celery
Step 4: Cut the end of the stalk of celery and take a look at the colors at the bottom of the celery and the leaves at the top of the stalk
Step 5: Place the celery into the red water
Step 6: Watch how the red water is absorbed through the stalk of celery over the next 2+ days, eventually the coloring should make its way up to the leaves

As one of the most interesting and essential actions that our bodies perform, capillary action is almost like having a billion tiny sponges in our body that help to push and circulate blood to all of our essential organs including our brain and our heart. Since blood is incredibly important, without capillary action we wouldn’t be able to survive.