Water roof at the parque das naçoes, Lisbon, Portugal
Water roof at the parque das naçoes, Lisbon, Portugal

Viscosity - a physical property of fluids. It shows resistance to flow. In a simple example, water has a low viscosity, as it is 'thin'. Syrup or tar, on the other hand has a high viscosity, as it is 'thick'. A way to test for viscosity is the speed at which the substance runs down a slope. Syrup would reach the bottom very slowly, whereas water would be a lot quicker.

Viscosity is a measure of the resistance of a fluid to being deformed. You can think of it as the fluid's internal resistance to flow, or its internal friction. For example, water has a lower viscosity than vegetable oil. Both, however, are newtonian fluids which maintain their viscosity whether you stir them slowly or quickly.

Viscosity varies widely with temperature. However, temperature variation has an opposite effect on the viscosity of liquids and gases.

Non-Newtonian Fluid (video 4:04) - one in which the viscosity changes depending on the force applied. This demonstration uses a mixture of cornstarch and water to create a non-newtonian fluid. When applying a quick or sharp force (such as running across the surface) the viscosity of the fluid increases, and it acts more like a solid. When applying a slow, steady force (such as standing still), the viscosity decreases and it acts more like a normal fluid.

More about viscosity
  • ketchup, motor oil
  • firm glass - yes, glass is a liquid and viscosity matters
  • liquid metal
  • mixtures


What's the problem?
Customers expect the applesauce they buy to the same from one jar to the next. This is a problem for the food processing company. Apples aren't all the same. Some a juicy, some aren't, so the applesauce making process has to be adjusted to the results are the same.
  • Ask - How runny should applesauce be? What do customers expect? What is the viscosity measurement for this kind of applesauce?
  • Imagine - How much difference is there in the apples coming into the food processing factory? How can the applesauce consistency be adjusted?
  • Design, Build - Each batch of apples is tested for juiciness. Depending on the results, the other ingredients in the batch can be adjusted. How much additional liquid needs to be added?
  • Improve - Each batch of applesauce is tested to ensure that it meets the standard. How can the process be adjusted to ensure that all batches of applesauce meet the standards? Do the standards need to be adjusted so the applesauce can be consistent?

That's engineering
  • density - a measurement that compares the amount, ratio, of matter an object has to its volume. An object with a lot of matter in a certain amount of volume has high density. An object with a little matter in the same amount of volume has a low density.
  • flux - flow per unit area, where flow is the movement of some quantity per time

Engineering ideas
  • fluid, viscosity, temperature, liquid, gas, pressure, solid, surface tension, density, expansion, volume, hydraulic system, wetting, non-wetting, capillary forces, flow, volumentric flux, density


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