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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].

0 votes
2 answers
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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 …
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2 votes
3 answers
1k views

Can beats be produced by two waves moving in opposite direction?

I've always seen beats to be produced when two waves are said to be moving in the same direction with different frequency. Can beats be produced by addition of waves moving in opposite direction ?
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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 …
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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 …
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0 votes
1 answer
205 views

Infinitesimal rotation vector [duplicate]

Chapter 4.8, Goldstein 3rd ed classical mechanics under infinitesimal rotations (p.166~167) ($\mathbf{B}$ is an orthogonal matrix and $\mathbf{r}$ is a position vector and $d\boldsymbol{\Omega}$ is t …
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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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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 …
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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?
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2 votes
1 answer
133 views

A doubt in a Wikipedia article discussing Bertrand's Theorem in Central force motion

Wikipedia on Bertrand's theorem, when discussing the deviations from a circular orbit says: ...The next step is to consider the equation for $u$ under small perturbations ${\displaystyle \eta \equiv …
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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 …
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0 votes
3 answers
238 views

Using Lagrange equation

In classical mechanics we have a concept of generalized coordinates. Say my generalized coordinates are $(x,y)$. My doubt is, Is it legal to write the position vector in any vector basis say polar ba …
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0 votes
0 answers
54 views

A thought experiment to prove that Newtonian gravity is incomplete [duplicate]

A particle is at rest in one frame having mass $m$. It'll attract another mass proportional to its mass ( newtons law) . We jump into another frame moving close to speed of light. In this frame it's m …
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0 votes
1 answer
20 views

Why does normal force decrease if a body rotates on and around another smooth body

We've an system of a sphere (Radius $R$) and a point particle of mass $m$. This particle is at rest on a smooth sphere, we've then $N=mg$ Now I poke it and it begins to revolve on and around it due to …
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1 vote
1 answer
64 views

How is kinetic energy $T$ given by $T=\dfrac{1}{2}\sum_{i}p_{i}\dot{q_{i}}$ in Hamiltonian a...

Im going through a website teaching Hamiltonian mechanics and I know the below $$-\dot{p}_{i}=\dfrac{\partial H}{\partial q_{i}} \tag{14.3.12}$$ $$\dot{q}_{i}=\dfrac{\partial H}{\partial p_{i}} \tag{1 …
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0 votes
1 answer
475 views

Transformation equations and generalized coordinates

Paraphrasing Goldstein If we've $N$ number of particles and there exist holonomic constraints, expressed in $k$ equations, then we may use these equations to eliminate $k$ of the $3 N$ coordinates, a …
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