Flow rate and Viscosity
Viscosity
- the property that describes a liquid (or gas) thickness or thinness.
- A thicker liquid is more viscous and has a higher viscosity. (for example, maple syrup is more viscous than water).
Flow Rate
- the volume of fluid that passes a point in a certain amount of time.
- How fast a fluid flows from point A to point B.
What properties of fluids might cause a liquid to speed up or slow down?
Answer:
1) the size and shape of the particles can affect viscosity. Large particles that are rough and bulky have a higher viscosity (and therefore lower flow rate) than fluids composed of small particles that are smooth and not bulky.
2) Temperature can affect viscosity. Adding heat, or energy, causes particles to move farther apart. Heating a liquid decreases flow resistance and decreases the viscosity. Cooling a liquid increases the viscosity and decreases flow rate.
Explore this in the lab on page 41: Determining Flow Rate.
Read page 40.
Product Performance and Viscosity
A product is developed for a specific use. In many liquid products the thickness is considered important (for practical and aesthetic reasons). Consider the following examples:
- face/hand creams à can’t be too gummy or oily
- shampoos must be viscous enough to cling to hair, but able to rinse out.
- pasta sauces, salad dressings and ice cream toppings shouldn’t be too runny or thick.
- What about make-up, nail polish, paint, engine oils, etc.
- What else?
Do the investigation on page 47, and discuss.
Read through pages 40-49. Make your own notes on page 48 and 49 – you are responsible for this! You should understand resistance to flow and how this concept relates to viscosity. You should also be able to describe how the viscosity of gases varies.
Then on page 49 à answer text questions #1-6