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# Fluid Materials watch

1. Please explain this! Thank you
2. Well the quick answer is that the coarse particles settle in less time than the fine particles... seems to be part of a multi part question so is there any clue in the earlier section as to what might cause that?
3. (Original post by Joinedup)
Well the quick answer is that the coarse particles settle in less time than the fine particles... seems to be part of a multi part question so is there any clue in the earlier section as to what might cause that?
Umm, there are questions but not related to this actually, thanks
4. (Original post by Joinedup)
Well the quick answer is that the coarse particles settle in less time than the fine particles... seems to be part of a multi part question so is there any clue in the earlier section as to what might cause that?
The mark scheme says
1) smaller particles reaches terminal velocity quicker
2) Viscous drag varies in proportion to radius but weight varies in proportion to radius cubed.
did not understand the 2nd point. please explain.
5. (Original post by Gartley222)
The mark scheme says
1) smaller particles reaches terminal velocity quicker
2) Viscous drag varies in proportion to radius but weight varies in proportion to radius cubed.
did not understand the 2nd point. please explain.
I believe you need to consider the equations relation density to weight and mass, as well as that for the volume of a sphere, to reach the second part of the second point. You can then relate this to the first point, which should be somewhere on the sylalbus.
6. (Original post by Gartley222)
The mark scheme says
2) Viscous drag varies in proportion to radius but weight varies in proportion to radius cubed.
did not understand the 2nd point. please explain.
Surface area of a sphere (I think the mark scheme should read radius squared)

Volume of a sphere
7. (Original post by uberteknik)
Surface area of a sphere

Volume of a sphere
thank you!!!! can you kindly tell me what does "Varies in proportion means" in easy language.
8. (Original post by Gartley222)
thank you!!!! can you kindly tell me what does "Varies in proportion means" in easy language.
it means if you change the radius of a sphere of whatever, then the viscous drag/weight will correspondingly change - in this case the changes are proportional, as stated in the mark scheme
9. (Original post by artful_lounger)
it means if you change the radius of a sphere of whatever, then the viscous drag/weight will correspondingly change - in this case the changes are proportional, as stated in the mark scheme
understood! thank you!!
10. (Original post by Gartley222)
thank you!!!! can you kindly tell me what does "Varies in proportion means" in easy language.
Literally, one variable changes in response to a different variable.

For instance, the speed of a car varies in proportion to the pressure applied to the accelerator pedal.

The temperature of the room varies in proportion to size of the gas fire flame.

The speed of descent varies in proportion to the liquid viscosity etc.
11. (Original post by uberteknik)
Literally, one variable changes in response to a different variable.

For instance, the speed of a car varies in proportion to the pressure applied to the accelerator pedal.

The temperature of the room varies in proportion to size of the gas fire flame.

The speed of descent varies in proportion to the liquid viscosity etc.
thank you!! got it.

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