Soapy Surface

Age range: 9-12 years

Duration: 20 minutes

Biomimicry Connection:

This activity shows the concept of surface tension in water, which is used by water striders to stay afloat and move on water surfaces. Understanding this principle not only visualizes the mechanism water striders use, it also provides a source of inspiration to solve human problems and create innovative designs.

Activity Details:

Tools and Materials

• Cotton buds
• Dishwashing soap (liquid form)
• Large plate or bowl
• Ground pepper

Description

This activity will help pupils to visualise surface tension.

1. Fill the plate with water.
2. Sprinkle some ground pepper over the surface.
3. Dip the cotton bud in the dishwashing soap. Now, touch the water surface.
4. What happens (soap breaks the water tension)? Why does the effect become less over time (there is already soap in the water)?

Water striders walk on water by using surface tension, and their hydrophobic leg hairs prevent them from breaking the water's surface, enabling them to stay afloat. This activity demonstrates this surface tension by adding pepper to the water and using dishwashing soap to disrupt water's surface tension, causing pepper to move away from the soapy point of contact.

Extensions

You could also use milk instead of water, and food colouring instead of pepper. The colours will give a cool effect once the cotton bud touches the surface.