When you use a paper towel to clean up spilled water, have you ever noticed how the water seems to be taken up by the towel? Small openings in the towel attract the water molecules. This is a force called capillary attraction, and it pulls the water into the towel. If you hold the paper towel vertically in a cup of water, you can see the water climb upward.

How high can you get the water to climb? Can you use this as a kind of “water ladder” to raise water to a higher level without a pump? This activity will help you explore these ideas.

Tools and Materials

• Small plastic cups, approximately 250 ml (8 oz)
• Water
• Paper towels or other absorbent paper
• 6 or more wooden blocks or other small blocks, each approximately 2 cm (0.79 in) high
• Spring clothespin or paper clip
• String
• Ruler

Optional materials:

• Food coloring
• Stopwatch

What to Do

1. Explore how capillary attraction works in your paper-towel material. Fold a paper towel several times to make a narrow strip. Use the string and clothespin or paper clip to suspend the folded paper towel above a cup of water. Lower the paper towel into the cup until it is in contact with the water, and then secure it in that position. We added blue food coloring to our water so that you can more easily see the movement of the water.

Watch for a few minutes. You can see the water go into the paper towel and move upward because of capillary attraction!

1. Measure how high the water rises in your paper towel. Write down your measurement for future reference.

1. Can you find a way to collect the water that has been pulled up into the paper towel? If so, you might be able to make a “water ladder” to pull up water without using a pump. As a preliminary activity, place two cups side by side, with one full of water. Fold a paper towel as before, but then fold it in half lengthwise and place the ends in the two cups. What do you think will happen to the water? Watch!

1. If the paper towel can move water from one cup to another cup next to it, can it transfer water to a cup that is up on a small block? Try it and see!