Newtonian Mechanics/Forces Question

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MyNameIsNicholas
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Member advised to use the homework template for posts in the homework sections of PF.
Two metal buckets hanging one below the other on cords, with a cord from the top of the upper bucket and a cord joining the two buckets.


These buckets are being suspended. The cords have no mass and each bucket is 3.5 kg.

a.) Find the tension in the upper cord (T1) and the lower cord (T2)
b.) If the apparatus is pulled upwards from the top of the upper cord, what are the new tensions of each cord?

I understand the first part. The force diagrams consist of:
(Upper Bucket): T1 upwards, T2 downwards, and Fg downwards
(Lower Bucket): T2 upwards and Fg downwards

However, when the apparatus accelerates upwards, the tensions in both cords increases. This makes sense physically but in the force diagram isn't force applied (causing acceleration) going upwards? And if that were the case, then force applied would counter-intuitively decrease the tension within the cords. Can someone graciously clear this up for me?
 
MyNameIsNicholas said:
Two blue metal buckets hanging one below the other on a vertical rope, with a handle on each bucket and a short connecting line between them.


These buckets are being suspended. The cords have no mass and each bucket is 3.5 kg.

a.) Find the tension in the upper cord (T1) and the lower cord (T2)
b.) If the apparatus is pulled upwards from the top of the upper cord, what are the new tensions of each cord?

I understand the first part. The force diagrams consist of:
(Upper Bucket): T1 upwards, T2 downwards, and Fg downwards
(Lower Bucket): T2 upwards and Fg downwards

However, when the apparatus accelerates upwards, the tensions in both cords increases. This makes sense physically but in the force diagram isn't force applied (causing acceleration) going upwards? And if that were the case, then force applied would counter-intuitively decrease the tension within the cords. Can someone graciously clear this up for me?
I'm not sure why you would believe that's the case, but look at ##\sum F = ma##. Solve for the tension, and you'll see why hopefully. You may be confusing systems in equilibrium and accelerating systems while doing the FD.

Edit, trying to think of a good way to explain what I think is catching you up, but anyway, what's actually accelerating the system upward? The reactionary tension of course! The force that's pulling the system upward itself isn't applied to the buckets, its mediated by the tension in the rope.

Not sure if that helps or not.
 
Last edited:
I think I understand! The FA isn't actually an applied force. Well it is, but in terms of this problem it isn't. It's actually just addition upward tensional force on the upper cord FT1! This would, obviously, increase FT1 and in turn increase FT2. Thanks for the help and sorry for not using the proper format of my question. Merci.
 
Attachments
  • Free-body diagram in a PowerPoint slide showing two blue boxes labelled Bucket 1 (upper) and Bucket 2 (lower), with arrows for tension forces FT1 and FT2 and a red arrow labelled FA pointing up on Bucket 1.
    upload_2016-1-17_21-59-26.png
    47.4 KB · Views: 565
  • Free-body diagram of two buckets: Bucket 1 (upper) has upward force FA, upward tension FT1, downward tension FT2 and weight FG; Bucket 2 (lower) has upward tension FT2 and weight FG.
    upload_2016-1-17_22-0-11.png
    5 KB · Views: 548
MyNameIsNicholas said:
I think I understand! The FA isn't actually an applied force. Well it is, but in terms of this problem it isn't. It's actually just addition upward tensional force on the upper cord FT1! This would, obviously, increase FT1 and in turn increase FT2. Thanks for the help and sorry for not using the proper format of my question. Merci.

Edit: Ignore those files. I was going to ask a follow-up question but upon creating those images and thinking about the question, it clicked!