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Old Jan 6th 2019, 03:22 AM   #1
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Tumble dryer problem

Hi guys, I've been stuck on this question for quite a while. The main issue I have is that when i resolve the centripetal force, its vertical component is downwards but in order to offset the downward weight shouldn't it be upwards? Am I doing something wrong? I got 75 revs/min but the answer in the book was 37 revs/min. Thank you.
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Old Jan 6th 2019, 03:50 AM   #2
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So the clothes fall away at 60 to the vertical , at this point the vertical component of the centrifugal force = the gravitational force.

m omega squared r cos 60 = m g

omega squared = 9,81/ 0.325 cos 60 = 60.37

omega =7.77 radians /sec ...x 60/2pi = 74.2 RPM
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Old Jan 6th 2019, 03:54 AM   #3
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Wrong answer?

Hi, thanks for the reply but the answer provided in the book was 37. Also i took "g" as 10 so theres some deviation between our answers
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Old Jan 6th 2019, 04:22 AM   #4
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Originally Posted by Mankind View Post
Hi, thanks for the reply but the answer provided in the book was 37. Also i took "g" as 10 so theres some deviation between our answers
Yep ...I double checked , I think the book must be wrong .
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Old Jan 6th 2019, 04:31 AM   #5
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Ah i see, thanks for your help. Do you think you can explain to me why the vertical component of the centripetal force ats downwards though? I thought it should act upwards so the clothes will not fall...
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Old Jan 6th 2019, 07:11 AM   #6
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Originally Posted by Mankind View Post
Ah i see, thanks for your help. Do you think you can explain to me why the vertical component of the centripetal force ats downwards though? I thought it should act upwards so the clothes will not fall...
Sure ... the vertical component of the centrifugal force acts pushing the clothes upward , gravity pulls them down ...

the centripetal force is exerted by the drum on the clothes pushing them inwards
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Old Jan 6th 2019, 04:32 PM   #7
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thank you
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Old Jan 7th 2019, 05:18 AM   #8
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There is often confusion between centrifugal and centripetal.

The centripetal force is the force applied to the clothes ,by the drum of the dryer, which pushes them toward the centre of the drum,
counteracting the inertial effect which would have the clothes carry on at a tangent to the drums rotation.

Centrifugal Force is an "apparent" force, equal to and opposite to the centripetal force.
The purists would say that centrifugal force does not exist,
however it can still be useful for calculating the results you want...
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Old Apr 21st 2019, 09:36 PM   #9
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When I was a child traveling on the bus with my my mum, she always said we fell to the right if the bus turned left because of centrifugal force. Even after growing up, that simple explanation has stayed with me.
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Old Apr 21st 2019, 10:15 PM   #10
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Talking

Who is the center if nothing else in cosmos?
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