Viscosity

The viscosity of a liquid is another term for the thickness of a liquid. Thick treacle-like liquids are viscous; runny liquids like water are less viscous.

This experiment should take 20 minutes. 

Equipment

Apparatus

• Eye protection, if desired
• Stopwatch
• Sealed tubes of different liquids (thermometer packing tubes are ideal)

Chemicals

Choose from:

• Water
• Cooking oil
• Washing up liquid
• Ethanol
• Shampoo or bubble bath

Health, safety and technical notes

• Read our standard health and safety guidance.
• Wear eye protection if desired.
• Ethanol is highly flammable, see CLEAPSS Hazcard HC040a.

Procedure

1. Take one of the tubes provided.
2. Ensure the bubble is at the top and the tube is held vertical.
3. Quickly invert the tube and measure the time it takes for the bubble to reach the top.
4. Repeat this measurement for all the samples
5. Complete a table, as shown below.

Notes

Remind students to time each liquid using a consistent method – eg measure the time from inversion until the ‘bubble first hits the top’. 

Questions

1. Which liquid is the most viscous?
2. Which liquid is the least viscous?
3. Design a different experiment for comparing the viscosity of liquids.