# What factors change viscosity, other than temperature?

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What factors change viscosity, other than temperature?
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What factors change viscosity, other than temperature?

An introduction from Mohamed Salah Hassan
We can say that viscosity is the resistance a material has to change in form. This property can be thought of as an internal friction.

To get a good feel for viscosity, I suggest that we first remember laminar flow. If a fluid or gas is flowing over a surface, the molecules next to the surface (the ones clinging to the walls) have zero speed. As we get farther away from the surface the speed increases. This difference in speed is a friction in the fluid or gas. It is the friction of molecules being pushed past each other. You can imagine that the strength with which the molecules cling together will be proportional to the friction. This strength is called viscosity. Thus, viscosity determines the amount of friction, which in turn determines the amount of energy absorbed by the flow.

The viscosity of a fluid is basically a measure of how sticky it is. Water has a fairly low viscosity; things like shampoo or syrup have higher viscosities. Viscosity also depends on temperature - engine oil, for instance, is much less viscous at high temperatures than it is in a cold engine in the middle of winter.

For fluids flowing through pipes, the viscosity produces a resistive force. This resistance can basically be thought of as a frictional force acting between parts of the fluid that are traveling at different speeds. The fluid very close to the pipe walls, for instance, travels more slowly than the fluid in the very center of the pipe.

Robert Harries says
The viscosity of a pure fluid changes most with temperature. Pressure has a small effect (much less than temperature) on the viscosity of a gas and the effect of pressure on a liquid is extremely small.