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Offline Muhammad Iqbal Khan

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Short Questions.
« on: 27/01/2008 11:38:09 »
i have few short question of you.

Q1: why liquid is preferred in Clinical Thermometers ?
Q2: Why does an acrobat holds a rod while walking on the rope ?
Q3: Why it is difficult to drive on the oily road ?





                                                            THANKS!!


 

Offline lightarrow

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« Reply #1 on: 27/01/2008 14:00:26 »
i have few short question of you.

Q1: why liquid is preferred in Clinical Thermometers ?
Q2: Why does an acrobat holds a rod while walking on the rope ?
Q3: Why it is difficult to drive on the oily road ?

1. How could you make a solid flow inside a thin glass pipe?
2. When an acrobat alone tilts of some degree, its center of mass tilts too, and this can make him fall if he's not so fast to correct his inclination. The rod increases very much his "moment of inertia" (along the axis of rotation of that tilt) and so every movement which makes him tilt is very much slowed down so he has plenty of time to correct his inclination.
3. Oil doesn't escape easily from the space between the wheel and the road so the static friction between road/wheel is replaced with dynamic friction of the wheel on the oil "film". The dynamic friction of a solid on a liquid is much less than static friction between two solids.
 

Offline daveshorts

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« Reply #2 on: 27/01/2008 14:32:18 »
Just an adjunct to 1 - and a gas is much harder to see. You can build gas thermometers, but you would need to put a piston in the top, which would probably stick, and or leak.
 

another_someone

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« Reply #3 on: 28/01/2008 14:37:36 »
Q1: why liquid is preferred in Clinical Thermometers ?
1. How could you make a solid flow inside a thin glass pipe?

You could have powdered solid flow.

Then again, solids don't need to flow in the same way - bimetal strips are used for some circumstances where one wants a simple thermometer that uses solids.  The are not as accurate as clinical thermometers, but they do work - so while I am not claiming that you can get solid based thermometers that work to the standards required of clinical thermometers (if one ignores electronic thermometers, that might be regarded as solid), but there is no technical impossibility to a solid thermometer, and we do have such devices (often as components of domestic heating control systems, where longevity, robustness,  and reliability are more important that than ultimate precision).

 

Offline lightarrow

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« Reply #4 on: 28/01/2008 14:50:18 »
Q1: why liquid is preferred in Clinical Thermometers ?
1. How could you make a solid flow inside a thin glass pipe?

You could have powdered solid flow.

Then again, solids don't need to flow in the same way - bimetal strips are used for some circumstances where one wants a simple thermometer that uses solids.  The are not as accurate as clinical thermometers, but they do work - so while I am not claiming that you can get solid based thermometers that work to the standards required of clinical thermometers (if one ignores electronic thermometers, that might be regarded as solid), but there is no technical impossibility to a solid thermometer, and we do have such devices (often as components of domestic heating control systems, where longevity, robustness,  and reliability are more important that than ultimate precision).

So, to measure a person's temperature do you advise the use of an oven thermometer, with all electric wires and an electric supply connected to it?  :)
(I'm joking, I know what you intended to say).
 

Offline daveshorts

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« Reply #5 on: 28/01/2008 15:47:13 »
Although you could build a thermometer based on powdered solid flow, it would be very difficult, as thanks to friction the density of a powdered solid is dependent upon how it has been treated recently - consider flour before and after sieving it.... this would make the temperature reading dependent upon recent temperature readings...
 

lyner

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« Reply #6 on: 28/01/2008 18:05:11 »
The point of a liquid-filled thermometer is that the liquid in the bulb expands and the very narrow tube causes a 'huge' movement of the liquid column; all the extra volume goes into the column. A gas thermometer could work  (and is used in some applications) but, to measure the actual volume of gas, you need either an 'ideal' piston for the gas to move or a liquid meniscus and fancy pressure-equalising  mechanism. The 'Gas Laws' involve three variables - pressure, temperature and volume, whereas the effect of pressure is minimal for liquids. The expansion of the glass envelope IS relevant in a mercury in glass thermometer but is 'factored in' during calibration.
 

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« Reply #6 on: 28/01/2008 18:05:11 »

 

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