IIT JEE , AIEEE Forum - Physics , Mechanics - WHAT WILL HAPPEN IF WATER INSIDE A BOB OF A PENDULUM FREEZES?.EFFECT ON TIME PERIOD?

claracishazephyr

THE BOB OF A PENDULUM IS HOLLOW AND HAS WATER FILLED IN.IF THAT WATER FREEZES WAT'LL HAPPEN AND WAT WILL BE THE EFFECT ON THE TIME PERIOD??PLEASE EXPLAIN THE REASON AS WELL FOR WATEVER HAPPENS.

biki

no change in time period occurs.
This is bcz T depends on effectiv length from point of suspension to C.G. of bob and on g.

Bob filled up with water has C.G> at centre and also if water turns to ice, the C.G. remains undisturbed..

ganesha1991

i think........
T increases
mass= density * volume
as mass remains constant
and density of ice is lower than water the volume increases
thereby lenght increases
T is directly proportional to l
therefore it increases

correct me if i'm wrong

prathyu

as it is a pendulum the time period is 2

^{[ ]}

l/g so it doesnt depend on the mass of the bob

if it is a time period of a loaded spring then mass comes into consideration

computer001

ive got a problem...the bob is fully filled wid water...now if it freezes then vol shoul increase buit it cannot inc as volume ob bob is fixed so what will happes will the bob break???

anandghegde

yes i believe

Decoder

bob will crack..or the arrangement can never happen by normal freezing..

computer001

or will the ice break up into fine powder or sumtin??
i mean i no this is not connected with the question but well..

eistien

yeah even i too think that as volume increases there is redistrbution of mass and centre of gravity changes its osition and effective length increases and thus time period increases and yeah computer i think you too are right it might crack!!!

anchitsaini

i think it would depend on various conditions like maybe elasticity of bob,etc
but i think we can ignore the fact of bob's breaking to get to a conclusion.

the only factor that can variate in time period is length

edit i wrote crap here

computer001

EDITED
if the bob does not break this means tht water is not completely filled..when there is water it will occupy only the bottom part of the bob..i mean the water in the bottom hemisphere of tht bob is more than tht in the upper hemisphere...so initially COM was centre now it has come down by dist 'x' say...when it freezes volume of ice increases...bottom hemisphere continues to be filled up but the vol filled up in the upper hemi will inc.. wat i mean is tht the diff in mass of ice in upper n lower hemi is lesser than in the case of water..which means in case of ice COM is a little higher than in the prev case...hence effective length decreases on freezing...so T shud decrease

im not sure abt this but pls look@ my argument on Pg2

anchitsaini

i think this is what might be correct --

when the water freezes , water expands and hence its COM should rise . now as no external force is acting on the bob and water system thus bob should go down so that the COM of the system remains at the initial position

thus length should increase or T should increase as length is measured from the centre of bob to the point of suspension

edited - the case considered is less than fully filled one

sagar90

time peroid will increase

computer001

hey cummon mate...wat r u saying?the string will expand??
u r cooling arnt u??
the moving of the COM can be correlated with the change in temp i think..i mean with heat energy and stuff

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