[tag:classical-mechanics] entails the study of the trajectory of bodies under the influence of forces. More specific subtopics are: [tag:newtonian-mechanics], [tag:lagrangian-mechanics], [tag:hamiltonian-mechanics] for point particles and [tag:fluid-dynamics], [tag:statistical-mechanics] and ...
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0answers
24 views
Equations of motion for bob-on-a-string — am I missing some terms?
The dynamics of a type of physical system I am currently studying are modeled in most of the literature by replacing the moving parts of the system by an equivalent set of pendulums. Parameters and ...
0
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0answers
17 views
What determines the motion in a Newton's craddle? [duplicate]
Let's say we have a Newton's cradle with five metal balls, each with a mass $m$. You pick up one and release it, and right before impact it has a velocity $v$. What determines weather the ball at the ...
2
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1answer
49 views
Energy in a wind instrument?
My physics teacher said that he saw a guy playing a very large wind instrument on TV, and the guy apparently calculated that the total energy present in the instrument when he was playing was almost ...
-2
votes
2answers
50 views
Magnitude of force to keep stick in equilibrium
Problem statement
A straight and homogenous stick with mass m is pressed against a wall with the force F. The stick is horizontal perpendicular against the wall. Given that the friction between the ...
2
votes
2answers
104 views
Principle of Least Action via Finite-Difference Method
I have to be honest, the principle of least action seems to me more of a religious claim one takes on complete faith, though of course I'm hoping this is just because I don't understand it. I tried to ...
0
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1answer
33 views
Energy of a cylinder rolling down a path
Problem statement:
A cylinder rolls without slipping down a hill. It is released from height h. What is its speed when it come down? The cylinder mass may be completely concentrated on the radius R, ...
0
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0answers
27 views
Relation between the period of rotation and the period of revolution of a satellite
I read somewhere that the tidal forces between the earth and the moon causes the equality between the 2 periods of the moon and that every planet-satellite system will evolve to this condition (like ...
-1
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0answers
37 views
If Galileo had an electronic scale [closed]
If Galileo had an electronic scale, capable of absorbing the collision (without breaking) of 1 Kg sphere dropped from the top of Pisa tower what would had been the maximum measurement registered after ...
1
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1answer
69 views
6 Story Building Swaying, Normal?
Preface:
I'm currently sitting at my desk on a 5th floor in a South Florida office building, as I was earlier this morning when I felt the building sway slightly. It wasn't continuous and the ...
9
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2answers
131 views
+50
Stability of rotation of a rectangular prism
I've noticed something curious about the rotation of a rectangular prism. If I take a box with height $\neq$ width $\neq$ depth and flip it into the air around different axes of rotation, some motions ...
3
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0answers
28 views
Is it possible to find a “replacement pendulum” for a system of two equal but perpendicular pendulums?
I ask this question, because at the end of this long day I'm just too dazed to derive the proofs myself (even though I know that I should feel ashamed for this).
So, the question:
Given two ...
2
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0answers
67 views
Small unclarity in proof of Noether's Theorem
I'm trying to understand the proof of Noether's Theorem in my Classical Mechanics class. We formulated it as follows:
A continous symmetry is defined as a flow $\phi^{\lambda}(q(t))$ which leaves the ...
-2
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0answers
57 views
Need some help, physics degree [duplicate]
Ok, so I am currently finishing my physical science ASS Of Arts transfer= computer science or physics BA currently and am taking a break to learn all I can before I go back and finish. Physics has ...
1
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1answer
111 views
Buoyancy Problem - Cubes in water
I have a tank with water (10 m high) , with an ideal seal at the bottom (water can't fall down, but can enter bodies).
I have a system of 6 cubes ( of polystyrene density= 20 Kg/m^3) with dimension ...
1
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2answers
62 views
Classical/Quantum Coin Toss
I am having a brainfreeze moment and have confused myself, help appreciated!
Classical Coin: Heads OR tails.
Quantum Coin: Superposition Heads AND Tails.
Classical Mechanics: Deterministic (in ...
-2
votes
0answers
44 views
How can we feel, that something changes over time? [closed]
From the point of view of quantum mechanics the evolution of the universe is linear.
That is, if the vector is written as a sum of components, its evolution is described purely in terms of evolution ...
19
votes
3answers
350 views
How many points are required to make a black box
I have a black box with an arbitrary mass distribution inside it. I want to replace that object with n point masses without changing any mechanical properties of the box (center of mass, total mass, ...
1
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0answers
24 views
Hamiltonian system: match transformations and constants of motion
I have a problem about the interpretation of an exercise.
Given the following Hamiltonian
$$H=\frac{\mathbf{p_0}^2}{2m}+\frac{\mathbf{p_1}^2}{2m}+\frac{\mathbf{p_2}^2}{2m}-2V(\mathbf{r_1}- ...
1
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0answers
58 views
A quicker way to verify that a function is a constant of motion?
I have three particles that we can indicate with $\alpha$ ($\alpha$=0,1,2), they are identified by the $r^i_\alpha$ coordinates and $p^\beta_j$ conjugata momenta ($\beta=0,1,2$ and $i,j=1,2,3$).
I ...
6
votes
0answers
81 views
When does a PDE solve a variational problem? [migrated]
I understand that for a functional $J[f]$ on the space of differentiable functions $f$ on some domain, setting $\delta J[f]|_{f=f_0} = 0$ yields a (possibly nonlinear) partial differential equation in ...
-2
votes
2answers
81 views
acceleration due to gravity [closed]
From the picture we can evaluate the vertical and horizontal component:
Given on a book:
The figure above shows a small mass connected to a string, which is attached to a vertical post. If the ...
0
votes
0answers
37 views
Dose the gravitational force produces precession in the spinning top?
I'm new at classical mechanics but the text book says there is the torque in the spinning top which generated only by gravitation. It is hard to explain the situation, I've add the link.
...
0
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2answers
59 views
Hamiltonian equations: can I divide a solution of motion for a constant?
I'm solving an exercise about Hamiltonian equations. I have followed the proceeding below. The results given by the book are different to mine because its first result is the half of mine (and the ...
1
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1answer
92 views
Solving equation of motion of two massive particle exerting the gravitational force each other
I'm trying to analyze the motion of the particles which exert the gravitational force each other. Let $M_1$, $M_2$ be the masses of the particles, and the equation of motion of particle $M_1$
$$
...
-1
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0answers
24 views
how to dot product in 3 dimensions? [closed]
i have two vectors, vector A = 12 and vector C = 15 . vector A makes 60 degrees clock-wise x-axis. vector C makes 45 degrees clockwise z-axis, 30 degrees counter-clockwise y-axis. i did not ...
22
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8answers
1k views
What is the Earth truly rotating about/revolving around?
Earth rotates on its axis and revolves around the sun, the sun revolves around the galaxy, the galaxy is also moving. So Earth's net rotation as observed from a fixed inertial frame consists of all ...
10
votes
3answers
377 views
Google interview riddle and scaling arguments
I am puzzled by a riddle to which I have been told the answer and I have loads of difficulties to believe in the result.
The riddle goes as follows:
"imagine you are shrunk to the size of a coin ...
-5
votes
1answer
72 views
0
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1answer
47 views
Addes mass forces: can a force depend on acceleration?
My friend and I had a little discussion about added mass forces.
I always interpreted "F=ma" as a cause-effect relationship, so I find rather uneasy to accept that the cause can instantaneously ...
0
votes
1answer
36 views
Kinetic rotational energy of a bar hooked to a coil
I have solved an exercise and I'd like to know if my proceeding about finding kinetic energy is correct or not, because this is the first time that I "meet" a situation like this.
"A bar has mass $M$ ...
0
votes
1answer
23 views
Doubt about coordinates and point of equilibrium
I'm solving an exercise about small oscillations and I have a doubt about coordinates that I have to use.
This is the text of the exercise:
"A bar has mass M and lenght l. Its extremity A is hooked ...
1
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1answer
40 views
A different proof for 6 degrees of freedom
I want a different proof of 6 degrees of freedom of a solid object made of $\ N$ particles. I am thinking along these lines:
Definition of rigid body is
$\ modulus[\vec{r_i}-\vec{r_j}]=constant \ ...
3
votes
4answers
146 views
Can Newton's laws be explained by Quantum Physics? [duplicate]
I have only basic knowledge of physics.
Could you please explain to me if a "Quantum" laws can theoretically (perhaps in the future?) be used to explain everything in macro levels?
I'm having ...
0
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1answer
47 views
Something about collision [closed]
A sphere P of mass m, travelling with speed $u$, makes a head-on collision with a stationary sphere Q also of mass m. After the collision, the velocities of P and Q are $v_1$ and $v_2$ ...
2
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0answers
68 views
What happens when a ball stops bouncing?
If I were to drop a bouncy ball onto a surface, each successive bounce will be lower in height as energy is dissipated. Eventually, however, the ball will cease to bounce and will remain in contact ...
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0answers
37 views
What formula is used to determine weight distribution using two people to lift 100 lbs over their head? [closed]
Trying to determine actual weight and force required to perform a two man deadlift of an container weighing 100lbs
1
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2answers
62 views
Deriving $T = F\ r = I\alpha$ for a rigid body
For a single point mass :
$\tau=F_{t}r=ma_tr=(m r^2)\alpha = I\alpha$
For multiple point masses bound together : $\sum \tau_i = (m_ir_i^2)\alpha = I\alpha$
But how do we go from that to $I\alpha = ...
3
votes
1answer
52 views
Intuitive explanation for why same force applied farther from a hinge causes larger angular acceleration than if applied closer?
A standard example of a problem involving torque is opening a door - the same force F applied far from the hinge causes a larger angular acceleration than if applied close to the hinge.
I always had ...
0
votes
2answers
138 views
Getting started with Landau Physics course [closed]
I want to learn Physics in my own time. I am an electrical engineer, working in the same field and am tremendously interested in Physics. I have heard a lot about the 10 book series of Landau ...
1
vote
1answer
67 views
Inclined plane question
An object, mass $m$ is placed on an incline, angle $\theta$. System is at equilibrium. coefficients of static and kinetic frictions are $\mu_s$ and $\mu_k$ respectively. Then:
1) What is the Total ...
2
votes
1answer
98 views
What is the distance traveled
the red dots represent a side view of path traveled, F is downward force and the tool used here is a pen placing parallel to the coin
I have newly started to study mechanical physics. based on study, ...
0
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0answers
65 views
stable equilibrium in the system
I'm trying to understand the solution of the following problem.
A solid cube of uniform density and sides of b is in equilibrium on top of a cylinder of radius R. The planes of four sides of the ...
0
votes
2answers
64 views
Wave function interpretation $y(x,t) = (0.35m)\sin(10\pi t-3\pi x + \frac\pi{4})$
Wave function interpretation $y(x,t) = (0.35m)\sin(10\pi t-3\pi x + \frac\pi{4})$
I used to deal with function with one variable
And now theres are two, how can I interpret them?
Is $10\pi$ still ...
4
votes
2answers
56 views
Why are some jenga pieces easier to remove than others?
Jenga is a game place with wooden blocks stacked on top of one another in an alternating pattern. Players take turns removing blocks from any layer and placing them on top.
As the game progresses ...
0
votes
1answer
50 views
Another Inclined plane question
I did the FBD, and I found too many variables which are not eliminating...Moreover, I believe this question is based on kinetic and static friction. But, $\mu$ here is ambiguously defined...How Do I ...
1
vote
6answers
317 views
Centripetal Force Acceleration
Suppose you want to perform a uniform circular motion . Then a body performing uniform circular motion horizontally needs an acceleration $= \frac{v^2}{r}$ at each point on the circular path with ...
4
votes
1answer
69 views
Peculiar Hamiltonian Phase space
I was solving an exercise of classical mechanics :
Consider the following hamiltonian
$H(p,q,t) = \frac{p^2}{2m} + \lambda pq + \frac{1}{2}m\lambda^2\frac{q^6}{q^4+\alpha^4}$
Where ...
1
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0answers
50 views
Why is the angle of impact complementary to the angle of launch in the simple equations for the range of a projectile?
I'm using the standard equation for the range of a projectile:
\begin{align}
d &= \frac{v\ \text{cos}\theta}{g} \left( v\ \text{sin}\theta + \sqrt{v^2\ \text{sin}^2\theta + 2gy_0}\right)
...
3
votes
3answers
161 views
Physical interpretation of Poisson bracket properties
In classical Hamiltonian mechanics evolution of any observable (scalar function on a manifold in hand) is given as
$$\frac{dA}{dt} = [A,H]+\frac{\partial A}{\partial t}$$
So Poisson bracket is a ...
2
votes
1answer
66 views
Physics of a cold and hot top
Imagine two tops made up of exactly one thousand atoms. One is kept at 4 degrees Kelvin, the other at room temperature.
1. Would they weigh the same given an arbitrarily precise scale in the Earth's ...
