viscosity

Everyday

1. (science) How thick and sticky a liquid is, and how slowly it flows. tree →
2. (science) How strongly a liquid or gas resists flowing; a high viscosity means it flows slowly. tree →

In the lessons

In science lessons you compare liquids: honey, treacle and syrup have a high viscosity and pour slowly; water and juice have a low viscosity and pour quickly. Heating usually lowers the viscosity of a liquid, so warm honey runs faster. A common experiment is timing a marble falling through different liquids. Phrases: "high viscosity", "low viscosity", "measure the viscosity".

Examples

• Honey has a higher viscosity than water. tree →
• We tested the viscosity of oil, syrup and water by timing how fast they ran down a slope. tree →
• Warm syrup has a lower viscosity, so it pours more easily. tree →
• Ketchup has a high viscosity, so it is hard to get out of the bottle. tree →
• Engine oil must have the right viscosity to work well. tree →
• The marble sank slowly because the liquid had a high viscosity. tree →

Note

Mostly uncountable. Adjective: viscous (thick and sticky). Trap: viscosity is not the same as density; oil is less dense than water (it floats) but has a higher viscosity (it flows more slowly). In a results table, a longer time to flow means higher viscosity.