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Dependence of viscosty on temperature!

For my A2 Physics coursework, I am investigating the effect of temperature on viscosity.

I wanted to know: what causes the viscosity of a substance (e.g. oil or molasses) to decrease, as the temperature is increased?
Reply 1
Avatar for Drummy
Drummy
10
if you are doing OCR B Physics you should have done about boltzmann's constant and activation processes.

Basically fluid flow is an activation process. The molecules are bound together but a very small fraction have the extra energy required to break their bonds and so the fluid "flows".
The fraction that have this required energy is the Boltzmann constant

i.e. fb=e−ϵkTf_b = e^-\frac{\epsilon}{kT}

when you increase the temperature of the fluid the probability of a molecule having enough energy to escape its bonds increses, roughly by double for every 20 degrees.

So higher temperature means more energetic molecules, more that can break their bonds, more flow.
Reply 2
Avatar for mumakil142
mumakil142
OP
3
Drummy
if you are doing OCR B Physics you should have done about boltzmann's constant and activation processes.

Basically fluid flow is an activation process. The molecules are bound together but a very small fraction have the extra energy required to break their bonds and so the fluid "flows".
The fraction that have this required energy is the Boltzmann constant

i.e. fb=e−ϵkTf_b = e^-\frac{\epsilon}{kT}

when you increase the temperature of the fluid the probability of a molecule having enough energy to escape its bonds increses, roughly by double for every 20 degrees.

So higher temperature means more energetic molecules, more that can break their bonds, more flow.

Thanks!
There was actually a question on a past paper I looked at which had this on, about the activation nrg for a water molecule to escape it's cage. Not sure what past paper though, I do some sort of OCR physics.

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