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Classical mechanics discusses the behaviour of macroscopic bodies under the influence of forces (without necessarily specifying the origin of these forces). If it's possible, USE MORE SPECIFIC TAGS like [newtonian-mechanics], [lagrangian-formalism], and [hamiltonian-formalism].

2 votes
2 answers
334 views

About virtual displacement

Thornton Marion The varied path represented by $\delta y$ can be thought of physically as a virtual displacement from the actual path consistent with all the forces and constraints (see Figure above …
1 vote
1 answer
513 views

Virtual displacement for a block sliding down a wedge

A block slides on a frictionless wedge which rests on a smooth horizontal plane. There are two constraints in this system. One that the wedge can only move horizontally and another that the block mus …
6 votes
3 answers
912 views

Angular momentum of a purely rotating body about any axis

It's proved in my K&K mechanics textbook that in pure rotation about an axis passing through the body it's angular momentum is $I\omega$. What about if I want to find the angular momentum about an ax …
8 votes
3 answers
4k views

Non-uniqueness of the Lagrangian

Goldstein, 3rd ed $$ \frac{d}{d t}\left(\frac{\partial L}{\partial \dot{q}_{j}}\right)-\frac{\partial L}{\partial q_{j}}=0\tag{1.57} $$ expressions referred to as "Lagrange's equations." Note that fo …
2 votes
2 answers
108 views

Help in understanding this derivation of Lagrange Equations in Non-Holonomic case

Whittaker, Analytical dynamics pg 215 I don't understand how we get the final equations relating $Q_r$ with $\lambda$ given the conditions above?
0 votes
1 answer
105 views

Virtual work of constraints in Hamilton‘s principle

Goldstein 2ed pg 36 So in the case of holonomic constraints we can move back and forth between Hamilton's principle and Lagrange equations given as $$\frac{d}{d t}\left(\frac{\partial L}{\partial \do …
0 votes
2 answers
444 views

Energy conservation equation for an object rolling up an incline [closed]

An sphere of radius $R$ rolls up an incline. We can write mechanical energy conservation equations for this motion because neither does the normal or the frictional force do any work. At the top of th …
0 votes
1 answer
192 views

What is 3-force in special relativity?

We define 4-force as one which satisfies: $\mathbf{f}=m \mathbf{a}$ where $\mathbf{a}=\frac{d \mathbf{u}}{d \tau}$. The quantities in bold face are 4-vectors. Hartle pg 88 defines a 3-force as: $\frac …
1 vote
1 answer
819 views

Conservation of angular momentum using symmetry properties

Goldstein pg 59 It can be shown that if a cyclic coordinate $q_{j}$ is such that $d q_{j}$ corresponds to a rotation of the system of particles around some axis, then the conservation of its conjugat …
0 votes
4 answers
751 views

Transformation equations from Generalized coordinates to rectangular

I've a proper set of generalized coordinates {$q_j$} ,$j=1...n$ for a system. This set determines the configuration of the system, also these can be used to determine the rectangular coordinates of al …
2 votes
2 answers
167 views

A doubt in a Wikipedia article discussing Bertrand's theorem

Wikipedia while deriving Bertrands theorem writes after some steps: ...For the orbits to be closed, $β$ must be a rational number. What's more, it must be the same rational number for all radii, sinc …
0 votes
2 answers
92 views

Why is this matrix symmetric?

Goldstein 3rd Ed, pg 339 In large classes of problems, it happens that $L_{2}$ is a quadratic function of the generalized velocities and $L_{1}$ is a linear function of the same variables with the fo …
0 votes
0 answers
65 views

Form of potential $V$ for conservative forces

Goldstein, Pg 21,3rd E.d writes only if $V$ is not an explicit function of time is the system conservative That means $V(r,\dot{r})$ is a conservative potential, however I think that only potentials …
0 votes
1 answer
243 views

Why Polhode is a circle in a symmetric body

Goldstein In the special case of a symmetrical body, the inertia ellipsoid is an ellipsoid of revolution, so that the polhode on the ellipsoid is clearly a circle about the symmetry axis. The herpol …
1 vote
0 answers
65 views

"Inertia tensor possess a type of revolution about Centre of mass" ? Can't understand this s...

Goldstein pg 194, 3rd Ed. $$ T_{\text {rotation }}=\frac{1}{2} I_{\alpha \beta} \omega_{\alpha} \omega_{\beta} $$ where $$ I_{\alpha \beta}=m_{i}\left(\delta_{\alpha \beta} r_{i}^{2}-r_{i \alpha} r_{ …

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