# Physics

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#1
I don't understand from where it says and onwards"..There are, however, liquids the dynamic viscosity of which is a function of the velocity gradient. .."

I am trying to understand the difference between Newtonian and non-Newtonian fluids from this text - would really like some help! Thanks!!

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1 year ago
#2
(Original post by h26)
I don't understand from where it says and onwards"..There are, however, liquids the dynamic viscosity of which is a function of the velocity gradient. .."

I am trying to understand the difference between Newtonian and non-Newtonian fluids from this text - would really like some help! Thanks!!

the ultra short version is that non-Newtonian liquids change viscosity when you stir (i.e. put a shear or velocity gradient) on them.

probably the most well known examples are:
cornstarch and water mixture which is liquid when static but which goes thick and virtually solid when sheared
non drip paint which goes runny when you shear it and thickens again when you leave it alone (this makes it as easy to apply with a brush as a very 'thin' paint - but as resistant to running after you've finished as a 'thick' paint.
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1 year ago
#3
(Original post by h26)
I don't understand from where it says and onwards"..There are, however, liquids the dynamic viscosity of which is a function of the velocity gradient. .."

I am trying to understand the difference between Newtonian and non-Newtonian fluids from this text - would really like some help! Thanks!!

when a liquid flows over a fixed surface.....the upper layer of that fluid gets greater velocity than the lower one....cos the lower one gets a resistive force due to the friction of that surface....

when a layer of fluid flows over a lower layer .....it gets a tangential force due to friction of lower layer.....
fluids that follow this equation are newtonian fluid and others are non newtonian fluid.....
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#4
(Original post by Joinedup)
the ultra short version is that non-Newtonian liquids change viscosity when you stir (i.e. put a shear or velocity gradient) on them.

probably the most well known examples are:
cornstarch and water mixture which is liquid when static but which goes thick and virtually solid when sheared
non drip paint which goes runny when you shear it and thickens again when you leave it alone (this makes it as easy to apply with a brush as a very 'thin' paint - but as resistant to running after you've finished as a 'thick' paint.
Thank you very much! Apologies for late reply as just came home. That makes sense. Just a few things:
When you kindly mentioned "put a shear or velocity gradient" do you mean that when you put some sort of stress like a force on the liquid which changes the velocity? What rules does it layout?

Am I right in saying Newtonian liquid does not change viscosity when you stir it?

Another thing that slightly confuses me are the rules of the Newton's law of viscous law:

So I understand how to use the formulas (just attached the notes and the formulas I need to know for this topic), I also even understood everything kindly explained by meek-boy .

But as stupid and idiotic as I sound, what is the point of the Newton's law of viscous law, what is it trying to explain? So it represents the viscosity and somehow tau represents it but I am sure there's more to it and also a way you can identify whether a fluid is Newtonian or not using this law's rules ( so when this law applies) or maybe mathematically using the formula.

A Non-newtonian fluid does not follow newton's law of viscosity as it changes viscosity when you stir it but how do you explain it with the law - what does the law say?

Sorry for all the rambling and for repetition of things that have probably been explained very well in this thread Attachment 794328
Last edited by h26; 1 year ago
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#5
(Original post by meek-boy)
when a liquid flows over a fixed surface.....the upper layer of that fluid gets greater velocity than the lower one....cos the lower one gets a resistive force due to the friction of that surface....

when a layer of fluid flows over a lower layer .....it gets a tangential force due to friction of lower layer.....
fluids that follow this equation are newtonian fluid and others are non newtonian fluid.....
Thank you very much!! This makes a lot of sense-confirmed a lot of things!!!
Would really appreciate if you could please kindly help me understand some of the things I don't understand - I have outlined it to Joinedup.
Once again really appreciate the help! Anyone who is helping is saving my life
Here it is:
Thank you very much! Apologies for late reply as just came home. That makes sense. Just a few things:
When you kindly mentioned "put a shear or velocity gradient" do you mean that when you put some sort of stress like a force on the liquid which changes the velocity? What rules does it layout?

Am I right in saying Newtonian liquid does not change viscosity when you stir it?

Another thing that slightly confuses me are the rules of the Newton's law of viscous law:

So I understand how to use the formulas (just attached the notes and the formulas I need to know for this topic), I also even understood everything kindly explained by meek-boy .

But as stupid and idiotic as I sound, what is the point of the Newton's law of viscous law, what is it trying to explain? So it represents the viscosity and somehow tau represents it but I am sure there's more to it and also a way you can identify whether a fluid is Newtonian or not using this law's rules ( so when this law applies) or maybe mathematically using the formula.

A Non-newtonian fluid does not follow newton's law of viscosity as it changes viscosity when you stir it but how do you explain it with the law - what does the law say?

Sorry for all the rambling and for repetition of things that have probably been explained very well in this thread
Last edited by h26; 1 year ago
0
1 year ago
#6
(Original post by h26)
Thank you very much!! This makes a lot of sense-confirmed a lot of things!!!
Would really appreciate if you could please kindly help me understand some of the things I don't understand - I have outlined it to Joinedup.
Once again really appreciate the help! Anyone who is helping is saving my life
Here it is:
Thank you very much! Apologies for late reply as just came home. That makes sense. Just a few things:
When you kindly mentioned "put a shear or velocity gradient" do you mean that when you put some sort of stress like a force on the liquid which changes the velocity? What rules does it layout?

Am I right in saying Newtonian liquid does not change viscosity when you stir it?

Another thing that slightly confuses me are the rules of the Newton's law of viscous law:

So I understand how to use the formulas (just attached the notes and the formulas I need to know for this topic), I also even understood everything kindly explained by meek-boy .

But as stupid and idiotic as I sound, what is the point of the Newton's law of viscous law, what is it trying to explain? So it represents the viscosity and somehow tau represents it but I am sure there's more to it and also a way you can identify whether a fluid is Newtonian or not using this law's rules ( so when this law applies) or maybe mathematically using the formula.

A Non-newtonian fluid does not follow newton's law of viscosity as it changes viscosity when you stir it but how do you explain it with the law - what does the law say?

Sorry for all the rambling and for repetition of things that have probably been explained very well in this thread

Newton's law of viscosity is only applicable for streamline motion......
If u apply force on a flow....which is streamline....it may change into turbulent motion.....so newton's law is not applicable......
.....for newtonian motion viscosity is just a number.....but for non newtonian motion.....it's a fuction of some varibles.....like shear stress or time...
if after stirring the flow remains streamline flow.....then the viscosity changes with the varibles....like A,F,dv,dz......the coefficient of viscosity is normally known as viscosity.....
0
1 year ago
#7
(Original post by meek-boy)

Newton's law of viscosity is only applicable for streamline motion......
If u apply force on a flow....which is streamline....it may change into turbulent motion.....so newton's law is not applicable......
.....for newtonian motion viscosity is just a number.....but for non newtonian motion.....it's a fuction of some varibles.....like shear stress or time...
if after stirring the flow remains streamline flow.....then the viscosity changes with the varibles....like A,F,dv,dz......the coefficient of viscosity is normally known as viscosity.....
oops .....i've attached the last pic incorrectly.....😁
i'm an indian.....are u from uk....???
I don't know anything about uk educational system.....but i've heard here is something called a level....are u studying at a level????I'm persuing physics ug course.....As english is not my mother tongue....do u have any problem to make out my words.....????
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1 year ago
#8
the last pic .....
this is a book of classical mechanics and general properties of matter....by an indian author....
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#9
(Original post by meek-boy)
the last pic .....
this is a book of classical mechanics and general properties of matter....by an indian author....
Ah wow! Thank you very much!!!!! This makes a lot of sense I understand it!!!
Really really appreciate the help and no, I have no problem understanding you - your English is fine

Many thanks once again!!!!!!!! Oh this is actually medical biophysics haha (1st year medic) but I put it under A level cause it is also in A level physics
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