6 wide mouth glasses or jars

Paper towels {use the kind where you can select a size}

Food dye or liquid water colors {red, yellow, and blue}

It’s a good idea to test your paper towel strip to make sure they fit properly in your glasses.  They should be able to go from the bottom of one jar to the next without sticking up in the air too much. The paper towel on the left shows the just-right height.

 First, line up the glasses and fill the first one with a good squirt of red watercolor, the third with yellow, and the fifth glass with blue.  Leave the other glasses empty.

Next,  add water to the glasses with color until the colored water almost reaches the top.

Move the glasses into a circle and add the paper towels.  Starting with the red, add one end of the paper towel and then put the other end in the empty glass next to it.

Continue around until the last paper towel was placed into the red glass. 

After several minutes, the colored water will travel the whole length of each paper towel.

After another five minutes, the water level will have dropped in the red, yellow, and blue glasses and rose in the once empty glasses as the water continued to travel from the more full glasses to the less full glasses.

 Not Working?

If you aren’t seeing much movement within a few minutes, it may be that you need to add more water to your colored water glasses.  It really needs to be almost at the top for the water to walk quickly.  So try topping off those glasses and seeing if that gets things moving.

If you see the water moving up the paper towel but it seems like it’s taking forever, it may be the type of paper towel you are using.  You want a paper towel that will really hold a lot of water.  

It really is worth the extra effort of trying different cups and paper towels to get this activity to work.  And once you have had success, don’t throw out those beautifully colored paper towels or the colored water!  

The Science Behind It

Capillary Action

The colored water travels up the paper towel by a process called capillary action. Capillary action is the ability of a liquid to flow upward, against gravity, in narrow spaces.  This is the same thing that helps water climb from a plant’s roots to the leaves in the tree tops.

Paper towels, and all paper products, are made from fibers found in plants called cellulose.  In this demonstration, the water flowed upwards through the tiny gaps between the cellulose fibers.  The gaps in the towel acted like capillary tubes, pulling the water upwards.

The water is able to defy gravity as it travels upward due to the attractive forces between the water and the cellulose fibres. 

The water molecules tend to cling to the cellulose fibers in the paper towel.  This is called adhesion.

The water molecules are also attracted to each other and stick close together, a process called cohesion.  So as the water slowly moves up the tiny gaps in the paper towel fibers, the cohesive forces help to draw more water upwards.

At some point, the adhesive forces between the water and cellulose and the cohesive forces between the water molecules will be overcome by the gravitational forces on the weight of the water in the paper towel.  When this happens, the water will not travel up the paper towel anymore. That is why it helps to shorten the length that colored water has to travel by making sure your paper towel isn’t too tall and making sure you fill your colored liquid to the top of the glass.