Physics Help Forum Tumble dryer problem

 Periodic and Circular Motion Periodic and Circular Motion Physics Help Forum

 Jan 6th 2019, 03:22 AM #1 Junior Member   Join Date: Jan 2019 Posts: 5 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. [ATTACH][/ATTACH] Attached Thumbnails
 Jan 6th 2019, 03:50 AM #2 Senior Member   Join Date: Apr 2017 Posts: 506 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 topsquark likes this.
 Jan 6th 2019, 03:54 AM #3 Junior Member   Join Date: Jan 2019 Posts: 5 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
Jan 6th 2019, 04:22 AM   #4
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 Originally Posted by Mankind 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 .

 Jan 6th 2019, 04:31 AM #5 Junior Member   Join Date: Jan 2019 Posts: 5 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...
Jan 6th 2019, 07:11 AM   #6
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 Originally Posted by Mankind 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

 Jan 6th 2019, 04:32 PM #7 Junior Member   Join Date: Jan 2019 Posts: 5 thank you
 Jan 7th 2019, 05:18 AM #8 Senior Member     Join Date: Jun 2016 Location: England Posts: 1,000 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... topsquark likes this. __________________ ~\o/~
 Apr 21st 2019, 09:36 PM #9 Junior Member   Join Date: Apr 2019 Posts: 5 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.
 Apr 21st 2019, 10:15 PM #10 Senior Member   Join Date: Mar 2019 Location: cosmos Posts: 558 Who is the center if nothing else in cosmos?

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