All Questions
Tagged with calculus classical-mechanics
61
questions
0
votes
0
answers
113
views
Question on non-holonomic constraints (This is different to the others)
I know there are many posts on non-holonomic constraints and also many on this exact one but I feel that there is still some confusion on it.
"Consider a disk which rolls without slipping across ...
- 207k
1
vote
1
answer
33
views
Derivatives of the lagrangian of generalized coordinates [closed]
I know that
$$U= \frac{1}{2} \sum_{j,k} A_{jk} q_j q_k \quad \quad T= \frac{1}{2} \sum_{j,k} m_{jk} \dot{q}_j \dot{q}_k $$
and the lagrangian is
$$ \frac{\partial U}{\partial q_k} - \frac{d}{dt} \...
- 11
0
votes
1
answer
54
views
What does this vertical line notation mean?
Here is the definition of the Noether momentum in my script.
$$I = \left.\frac{\partial L}{\partial \dot{x}} \frac{d x}{d \alpha} \right|_{\alpha=0} = \frac{\partial L}{\partial \dot{x}} = m \dot{x} = ...
- 207k
0
votes
1
answer
163
views
The derivative of rotational kinetic energy in terms of period gives me the wrong answer. Why should I use the product rule? [closed]
This is my first question here so I hope I do it correctly. I've tried to solve this, and google it, but I can't find the answer to this particular question. This equation comes from Carroll and ...
5
votes
2
answers
922
views
Rigorously prove the period of small oscillations by directly integrating
This answer proved that
$$\lim_{E\to E_0}2\int_{x_1}^{x_2}\frac{\mathrm dx}{\sqrt{2\left(E-U\!\left(x\right)\right)}}=\frac{2\pi}{\sqrt{U''\!\left(x_0\right)}},$$
where $E_0:=U\!\left(x_0\right)$ is a ...
- 70.2k
0
votes
1
answer
173
views
Time to travel a set distance given variable acceleration
Trying to solve a problem for the acceleration of an automated shuttle car at my work, been a while since I studied this stuff so thought I'd reach out for help.
I have a shuttle car that is tasked ...
- 9,508
-1
votes
1
answer
63
views
Derivative of distance [duplicate]
I know that $speed = |\frac{\vec{dr}}{dt}|$
and first derivative of distance with respect time will be $\frac{d\vec{|r|}}{dt}|$
These 2 expressions don't seem to represent the same thing. But when I ...
- 1,775
1
vote
0
answers
37
views
Is $n_{cr}=\frac{60}{2\pi}\sqrt{g\frac{\Sigma m_iy_i}{\Sigma m_iy_i^2}} =\frac{60}{2\pi}\sqrt{g\frac{\int y_idx}{\int y_i^2dx}}\quad ?$
I have a question about this formula used to calculate the first critical speed of a drive shaft.
$$
n_{cr}=\frac{60}{2\pi}\sqrt{g\frac{\Sigma m_iy_i}{\Sigma m_iy_i^2}} \tag {1} \quad .$$
It is the ...
- 8,094
0
votes
3
answers
432
views
Goldstein: derivation of work-energy theorem
I am reading "Classical Mechanics-Third Edition; Herbert Goldstein, Charles P. Poole, John L. Safko" and in the first chapter I came across the work-energy theorem (paraphrased) as follows:
...
- 126k
6
votes
7
answers
229
views
Is every $dm$ piece unequal when using integration of a non-uniformly dense object?
When we want to find the total charge of an object or total mass, usually we start off with a setup such as:
$$ m = \int dm \:\;\:\text{or} \:\;\:q = \int dq$$
in which we then use (and to keep it ...
- 13.1k
2
votes
2
answers
298
views
Solving for the radius of a sphere as a function of time
I have tried to realistically model the famous game Agar.io, which can described as the following: A sphere of initial mass $m_0$ expels part of its mass at a given rate ($\frac{dm_l}{dt}$) for thrust ...
- 19
0
votes
1
answer
43
views
Doubt in derivation of bending of beam, It's about derivatives and intergration
Radius of curvature of the beam in above picture is given as:
$$ \frac{1}{R} = \frac{d^2 y}{dx^2}$$
Please help me two points used as steps of a derivation in my book:
How was the radius of ...
- 207k
0
votes
0
answers
41
views
Minimum seperation of moving objects doubt
Let there be $2$ objects $P_1$(initial velocity $u$ $ms^{-1}$ & acceleration $a$ $ms^{-2}$) & $P_2$ (initial velocity $U$ $ms^{-1}$ & acceleration $A$ $ms^{-2}$) initially separated by ...
1
vote
2
answers
226
views
Confused about the solution to the pendulum differential equation
So I’ve learned how to derive the exact solution to the pendulum differential equation (in respect to its period), $\ddot{\theta} + \frac{g}{l}\sin\theta=0$, where $g$ is gravitational acceleration ...
- 113
1
vote
1
answer
114
views
Brachistochrone Problem without Trigonometric Substitution
I'm trying to numerically reproduce the cycloid solution for the brachistochrone problem. In doing so, I eventually ended up with the following integral:
$$ x = \int{\sqrt{\frac{y}{2a-y}} dy} $$
...
- 25k