How many pennies can you add to a glass filled to overflowing with water?
The photo shows a penny being added to a glass filled to overflowing with water. Notice how the penny pushes the surface of the water down. This is because the water molecules on the surface of the the water are attracted to each other in a way that creates tension.
Tension is a type of stretching force, thus the surface water molecules are stretched across the water much like a thin film. The penny must push through this film of water.
Surface tension is a physical property of liquids.
Surface tension is due to the cohesive forces between the surface liquid molecules.
Surface Tension Investigation Idea by *Mary Bowen.
As a demonstration, fill a 1-quart wide mouthed jar with tap water.
Ask students to guess how many pennies can be added to the jar of water before one drop of water spills over the edge.
The actually number of pennies is several hundred depending on the surface area of the jar or glass used.
This is always fun! But you have to have lots and lots of pennies!
Matter and Energy
Matter can be classified (identified) based on physical properties, such as surface tension.
Force, Motion, and Energy
Tension is a type of stretching force ; Surface tension is the force that stretches liquid molecules across the surface of the liquid.
* Mary Bowen is a fifth grade science teacher who is passionate about making difficult science concepts within the reach of every science student. She has a Master’s degree in Curriculum and never tires of creating dynamic lessons that inspire students to invent, experiment, and become scientists!