How to Demonstrate Surface Tension using a Paper Clip

Demonstrating Surface Tension of Water -- Surface tension is a property of water in which the molecules of water on the surface of the liquid is attracted to each other. The surface tension of water allows objects of greater density to be supported on the surface of the water. The attraction of a molecule to itself is called cohesion and attraction between two different molecules is called adhesion. The paper clip floating on the surface of water is a great example which demonstrates to your children how surface tension of water works. Surface tension is what allows small insects to walk on the surface of water; or, what allows dust and leaves to float on the surface of water. Surface tension in conjunction with cohesion is what allows the surface portion of a liquid to form drops such as water drops.

What you will need:
Bowl, glass, or beaker
Paper towel
Medal paper clip
Soapy water
Dropper

How to Demonstrate Surface Tension
Fill a bowl, glass, or beaker with water. Float a small piece of paper towel on the surface of the water. Place the paper clip on top of the paper towel. Carefully push the sides of the paper towel down into the water until the paper towel is no longer touching the paper clip. Carefully remove the paper towel from the water. The paper clip should easily remain floating on the surface of the water unless it is disturbed or bumped.

To Demonstrate How Soap (Surfactant) Breaks the Surface Tension

Separately mix some soap with water.

Using a dropper add a couple drops of soapy water to the surface of the water with the paper clip floating on it – be careful to add it to the water away from the paper clip. The soapy water should break the surface tension of the water causing the paper clip to fall to the bottom of the container. If it doesn’t work immediately give it a few seconds or add a few more drops of soapy water.

This is a great time to ask your children or student’s why they think soapy water caused the paper clip to fall to the bottom.

This is a great bell-ringer for science class. Have the student’s try to explain why the paper clip is floating. This is also great way to help your young children become or stay interested in science.

Mercury is a great example of how surface tension allows the element to form a cohesive ball.

Water beading on a freshly waxed car forms a sphere because of the water’s surface tension.

The separation of oil and water is caused by several different properties of the liquids, to include the differences in the surface tension of the liquids called “interface tension”.