Some fun with physics
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2 identical spheres of identical internal energy, One was place at a perfectly insulated flat floor while the other is attached to a string and tied to ceiling. Assuming no heat loss to surrounding(i.e perfect insulation), equal amt of heat is then supplied to both sphere and the both sphere expanded. After the expansion,which sphere has higher internal energy?
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I never study Thermodynamics leh..
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Originally posted by Darkness_hacker99:I never study Thermodynamics leh..
why not...it is fun -
O level dun hav..Originally posted by Hamiltonian1125: why not...it is fun
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that is O level question, pure phys? ?? .. more heat can pass throught the 1 wif string ba?? then the 1 wif no string attanch have higher internal energy ba?
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I think TS is armed with masters leh..Originally posted by ultimacloud:that is O level question, pure phys? ?? .. more heat can pass throught the 1 wif string ba?? then the 1 wif no string attanch have higher internal energy ba?
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go with this:
the one on the ceiling is facing a slightly lower pressure from the atmosphere and will therefore expand a bit more..
the rest of it is thermodynamics
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Hi bear bear
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yeah i think so tooOriginally posted by the Bear:go with this:
the one on the ceiling is facing a slightly lower pressure from the atmosphere and will therefore expand a bit more..
the rest of it is thermodynamics -
Assuming no heat lost to surrounding as stated in qns. So no heat lost thru string......Originally posted by ultimacloud:that is O level question, pure phys? ?? .. more heat can pass throught the 1 wif string ba?? then the 1 wif no string attanch have higher internal energy ba? -
E one with string.
Since no energy needed to expand when e other sphere is expanding...
E one tied to string needs to expand against atmosphere only...
I think la -
more work is done by the one on the string than the one on the floor.
so the one on the floor has greater internal energy. -
Can someone explain the relationship of gravitational force to internal energy? I long time ago read it but not forget liao.
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why suddenly so many physics qns....
ahh lost touch with physics straight after my o hahaa -
hahaz. I didnt take physic in O leh.. I only got Chemistry and BiologyOriginally posted by Hocklez:why suddenly so many physics qns....
ahh lost touch with physics straight after my o hahaa
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hmm the lost be very very little then....ur ans is correct in infinitesimal scale...but I am looking for a better one...Originally posted by the Bear:go with this:
the one on the ceiling is facing a slightly lower pressure from the atmosphere and will therefore expand a bit more..
the rest of it is thermodynamics
Hint: 1st law of thermodynamics -
i got 3 of them but physics is the one i usually slept thru...Originally posted by Darkness_hacker99:hahaz. I didnt take physic in O leh.. I only got Chemistry and Biology
ok la only B graded. haha... at least i passed! -
Both spheres are identical, hence, work done in pulling string and work done is pushing floor should be same by newton 3rd law....close close u are thinking along the right track..Originally posted by OO_OO_OO:more work is done by the one on the string than the one on the floor.
so the one on the floor has greater internal energy. -
the sphere on the string still does more work cos the one on the floor has to do work against its own weight during expansion?Originally posted by Hamiltonian1125:hmm the lost be very very little then....ur ans is correct in infinitesimal scale...but I am looking for a better one...
Hint: 1st law of thermodynamics -
... -__-" i wrong T__T
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hmmm using N3L, the one on string has to work against tension of string which is equal to its weight which is the same amount of work done as the one on the floor......use force dig to visualizeOriginally posted by OO_OO_OO:the sphere on the string still does more work cos the one on the floor has to do work against its own weight during expansion? -
Issit the one tied to the ceiling got more internal energy?
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Originally posted by Darkness_hacker99:Issit the one tied to the ceiling got more internal energy? that is right!
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v -
Here goes the solutions...
using 1st law of thermodynamics, since assuming no heat lost this implies internal energy can only change via work done.
Many of u think along this line....I really lurve u ppl for being so smart.
Now as heat supplied is equal, expansion is the same since the the tension and the reaction force by the floor are equal(use newton 3rd law).
Now the tricky part is here.....as the floor sphere expand,it does work against gravity as its centre of mass rises.
For the string's sphere, it does do equal work against the string but its centre of mass DROP as it expands, hence the loss of gravitational potential energy COMPENSATE the work done against the string. Hence, the one on string loses no energy but the one on floor loses energy as it work against gravity to expand which causes a corresponding in its centre of mass...
Darkness is right to relate gravity with internal energy....