Add learning objectives to each chapter

[moorepants]

• Jupyter and Python
• SymPy
• Orientation of Reference Frames
• Vectors
• Vector Differentiation
• Angular Kinematics
• Translational Kinematics
• Holonomic Constraints
• Nonholonomic Constraints
• Mass Distribution
• Force, Moment, and Torque
• Generalized Forces
• Unconstrained Equations of Motion
• Simulation and Visualization
• Three Dimensional Visualization
• Equations of Motion with Nonholonomic Constraints
• Equations of Motion with Holonomic Constraints
• Exposing Noncontributing Forces
• Energy and Power
• Equations of Motion with Lagrange's Method
• Unconstrained Equations of Motion with the TMT Method

[Peter230655]

I should see this with this link, correct? Thanks! https://moorepants.github.io/htmlpreview/?https://github.com/moorepants/learn-multibody-dynamics/blob/preview-pr-125/index.html

[moorepants]

You should see the ones for the SymPy chapter on that link.

[moorepants]

Sorry, the link you show doesn't exist. This is an issue not a PR. Only pull request's create previews.

[Peter230655]

Exposing Noncontributing Forces
In fig. 50, you show $T_1$ acting on $O$ and acting on $P_1$.
Should one of them technically not be $-T_1$ ? Same for $T_2$.
In the code below eq(211), you use $-T_2$ acting on $P_1$, and $T_2$ acting on $P_2$

[Peter230655]

Below the code under fig 50 you write:
Both pendulums’ configuration are described by angles relative to the vertical direction.
When I wrote my multi link pendulum, initially I described the location of frame A[i+1] relative to A[i], and the number of operations 'exploded' with the number of links. Only after I did it like you do it here, the number of operations became normal.
I think, you mentioned earlier in your lecture, that picking 'smart' generalized coordinates affects the resulting equations. Maybe worth mentioning this again?

[Peter230655]

Below eq(212) you write:
It is important to note that these scalar equations are linear in both the time derivatives of the generalized speeds u˙1,u˙2 as well as the two noncontributing force magnitudes T1,T2 and that all four equations are coupled in these four variables.
1.
As long as the forces in eq(212) do not depend on d/dt($dot u_i$ in a non-linear way, I think, the statement follows from eq(212).
Could there be a situation, where F = f(d/dt($dot u_i$, parameters), with f(..) non-linear?
2.
I guess the statement for the $T_i$ is an immediate consequence of their definition: One simply adds them to the bodies?

[Peter230655]

In fig(51), $u_3$ must be parallel to $T_1$, as you mention above the figure, (same with $u_4$), but does their sign matter? Must, say, $u_3$ be parallel to $T_1$ and point in the same direction?

[Peter230655]

Under the heading Auxiliary Generalized Inertia Forces you write:
....but the acceleration of the particles need not include u3 and u4, because they are equal to zero because u3 and u4 are actually equal to zero.
If one is pedantic, I guess, one would write like: ...actually equal to zero for all t ?
I guess, this is understood from the context.

[moorepants]

Hi @Peter230655, you've added these comments to the incorrect issue. This issue is about learning objectives.

[Peter230655]

I am not surprised!😩
How do I find the right issue?
I just read this chapter again this morning, understood it better, and thought I had noticed some points.

[moorepants]

All issues and pull requests are listed under those two tabs:

https://github.com/moorepants/learn-multibody-dynamics/issues

https://github.com/moorepants/learn-multibody-dynamics/pulls

There are "open" and "closed" issues/pull requests. You can always open a new issue with your comments if you can't find one to add to.