Is the transfer from 2D mechanics to 3D mechanics intimidating?

  • Context: Undergrad 
  • Thread starter Thread starter Femme_physics
  • Start date Start date
  • Tags Tags
    2d 3d Mechanics
Click For Summary

Discussion Overview

The discussion revolves around the transition from 2D to 3D mechanics, exploring the challenges and learning curve associated with this shift. Participants share their thoughts on whether the skills developed in 2D are applicable in 3D contexts, and they discuss specific problems related to calculating forces and moments in three dimensions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • Some participants express curiosity about the additional learning required when moving from 2D to 3D mechanics.
  • Others argue that 3D mechanics can be managed with conventional algebra, but vector algebra is more convenient, especially when familiar with parametric notation.
  • One participant suggests that classical mechanics is inherently 3D, and the transition is not as difficult as it seems, as many problems can be simplified by identifying symmetries.
  • There are discussions about specific problems involving moments and forces, with participants debating whether to use diagonal or horizontal distances in calculations.
  • Some participants mention the inertia tensor as a potentially intimidating aspect of 3D mechanics, but they also note that it is easier than it sounds.
  • There is a suggestion that while many simple systems can be reduced to 2D, there are exceptions, such as modeling charged particles in magnetic fields.
  • Participants share their experiences with specific problems and seek clarification on how to visualize and calculate forces in 3D scenarios.
  • There is a mention of a potential error in a solution manual, leading to further discussion about the correctness of certain diagrams and calculations.

Areas of Agreement / Disagreement

Participants generally express a mix of reassurance and uncertainty regarding the transition from 2D to 3D mechanics. While some agree that simplifications are often possible, others highlight that not all problems can be reduced to 2D, indicating a lack of consensus on this point.

Contextual Notes

Some discussions involve specific calculations and visualizations that may depend on individual interpretations of diagrams and problem setups. There are references to solution manuals that may contain errors, which adds to the complexity of the discussion.

Who May Find This Useful

This discussion may be useful for students transitioning from 2D to 3D mechanics, educators seeking to understand common student concerns, and anyone interested in the nuances of applying mechanics in three dimensions.

  • #31
In which direction will it move then?
Rotating counterclockwise
Edit: the movement is prevented by a combination of Tad and Foa.

That's what I think also!
 
Physics news on Phys.org
  • #33
Just a pointer, when you have a hinge, it can only produce reactions co-linear to the resultant force you are applying, which is probably why your book's solution is like it is :) (although the way it's drawn it doesn't look like it can actually move towards the negative y axis, since the rotation is blocked by the wall) Also, your solution manual should also have a moment at C, unless it assumes that there are joints in either E or C (which it probably does)
 
  • #34
Since you are not given any other information, I assume triangle ABC is horizontal.

Therefore there is only one force in the frame that can balance the moment of W about BC, that is the compression in strut AD. (can you see why AD must be a strut?)

This should get you started.
 
  • #35
Femme_physics said:
Rotating counterclockwise

That's what I think also!

What will it be? Will it move or not?
 
  • #36
I like Serena said:
What will it be? Will it move or not?

If any of the cords are snipped, it moves.
 
  • #37
Femme_physics said:
If any of the cords are snipped, it moves.

But I thought the other cord and the stick itself would block the movement? :confused:

Btw, did you try to do the math and find all the internal forces?
Can you solve the system assuming it is in equilibrium?
 
Last edited:
  • #38
But I thought the other cord and the stick itself would block the movement?
Well EVENTUALLY it would have to come to a halt. It will move until it assumes a new equilibrium position.

Btw, did you try to do the math and find all the internal forces?
Can you solve the system assuming it is in equilibrium?

Yes I did, I solved the problem I just don't have it here since I forgot my USB drive at home :( I'll post it later though :smile:

Much appreciated!
 
  • #39
What happened to post#32?
 
  • #40
Studiot said:
What happened to post#32?

Sorry. I was trying to solve it today but it appeared too long, but I did notice it just all boils down to the method of joints (after I peaked at the manual). Only treated in 3D. But same method applies :)

Your comment was spon on though, and exactly how I started solving it. Sigma Fy appears to give me my first result, and since the first step is the hardest, I think everything is just a matter of numbers thenceforth. :smile: thanks.

At any rate, It doesn't appear that hard anymore, just kinda long. I might get to it sooner or later.
 
  • #41
Femme_physics said:
Well EVENTUALLY it would have to come to a halt. It will move until it assumes a new equilibrium position.
Yes I did, I solved the problem I just don't have it here since I forgot my USB drive at home :( I'll post it later though :smile:

Much appreciated!
I don't remember if I had posted the solution in the other thread abut the problem but here it is!

http://img11.imageshack.us/img11/830/800sum7.jpg
 
Last edited by a moderator:
  • #42
This will take me a little more time than I have right now.
Are you here in the evening?
 
  • #43
Yes, but can we worry about the other threads first? See, I'm not worried about this since we agreed we got the right answers, I'm more worried about getting the right answers to the other stuff before the test tomorrow! :rolleyes:
 
  • #44
Femme_physics said:
I don't remember if I had posted the solution in the other thread abut the problem but here it is!

http://img11.imageshack.us/img11/830/800sum7.jpg

In your yx-view you have an equation for sum MO, which is not correct.
You forgot the moment of TADy.

You will find that if you add TADy, you can not solve the system (too many unknowns).

Effectively you snipped cord AD and solved the system!
(And so, with the cord snipped, it will not move, but it will be in equilibrium :wink:)

This is a statically indeterminate system, meaning there is more than 1 solution.
In your case, you have to effectively snip 1 of the 2 cords to be able to solve the system.
In practice the forces would divide themselves over the 2 cords depending on material properties.For reference, if you snip cord AD (what you did), the solution has:

Ox=0 N
Oy=866 N
Oz=900 N

TCDxy=1732 N

TADy=0 N (since it is snipped)
And if you snip cord CD, the solution has:

Ox=1500 N
Oy=866 N
Oz=900 N

TCDxy=0 N (since it is snipped)

TADy=866 N
 
Last edited by a moderator:
  • #45
You will find that if you add TADy, you can not solve the system (too many unknowns).

Tab doesn't act on the y plane
 
  • #46
Good morning Fp! :smile:

I write AD, you respond with AB.
Do you mean to say there is no cord between A and D?
 
  • #47
Well there is no "Tad", so if anything, you invented a wire! :P
 
  • #48
Now I understand why our discussion didn't go anywhere! :smile:

Apparently you were thinking I was talking about AB, when I was talking about the non-existing cord AD.
 
  • #49
Ah, so there is no cord AD? So I was right? :wink:
 
  • #50
That depends...
Did you sneak in and remove the cord while I wasn't watching? :-p
 
  • #51
What? No! There were always only two cords! Can't believe you're suspecting me, is this what our marriage based on?!? :-p

But, seriously, two cords. When did you go on inventing a cord?
 
  • #52
Playing tricks on each other that work out funny? Definitely! :approve:

The very first time I looked at the picture I immediately saw a cord between A and D, and I thought: Hey, that's a funny problem! :smile:

And when you had the question: "In the solution manual they appeared to have ignored it [Ed. CD]! i.e. not even include it as a vector! This is false, right?"
I drew the wrong conclusion they had removed CD to make the problem solvable.

Looking more carefully at the picture, I guess AD was not intended as a cord.
 
  • #53
And when you had the question: "In the solution manual they appeared to have ignored it [Ed. CD]! i.e. not even include it as a vector! This is false, right?"
I drew the wrong conclusion they had removed CD to make the problem solvable.

I was referring to Tcdx when I said that! That's what they completely seemed to ignore!

Looking more carefully at the picture, I guess AD was not intended as a cord.
Yea, it's not mentioned in the question, it's just a line to define the shape I guess, but I can see why you got confused! :smile:
 

Similar threads

Undergrad [Questions] Modeling a Baseball Pitch Trajectory in 3D Space
  • · Replies 1 ·
Replies
1
Views
2K
3D printers for mechanical engineering
  • · Replies 1 ·
Replies
1
Views
2K
2D vs 3D Method of Characteristics for Rocket Nozzle Design
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad Why does quantum mechanics believe that gravity is a field?
  • · Replies 10 ·
Replies
10
Views
3K
Classical Undergrad book on Classical Mechanics
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Statistical physics in 2D world: How to simulate gas and its interaction with objects? (game design)
  • · Replies 6 ·
Replies
6
Views
2K
How Does Dimensionality Affect Phonon Polarizations?
  • · Replies 1 ·
Replies
1
Views
1K
High School Answer: Basic Physics Question - Free Fall in 2D or 3D?
  • · Replies 22 ·
Replies
22
Views
4K
Undergrad Calculating Pitch and Roll Relative to a Velocity Vector from IMU Data
  • · Replies 5 ·
Replies
5
Views
4K
Heat transfer in wing by anti-ice system using hot air in piccolo tube
  • · Replies 6 ·
Replies
6
Views
2K