Classical mechanics refers to the classical (i.e., non-relativistic, non-quantum) study of physics. Three major formulations of classical mechanics are newtonian mechanics, lagrangian mechanics, and hamiltonian mechanics. The latter two are rather useful in extensions to Classical Mechanics; ...

learn more… | top users | synonyms (1)

9
votes
3answers
3k views

Hamiltonian is conserved, but is not the total mechanical energy

I wondering about the interpretation for the energy difference between the Hamiltonian and the total mechanical energy for systems where the Hamiltonian is conserved, but it is not equal to the total ...
0
votes
1answer
845 views

Energy used to stop / slow an object

I'm trying to workout how much energy (if any), I use (imagining me as an efficient machine rather than a complex bio-mechanical human) when I lower or catch a weight. I understand that when I push it ...
0
votes
0answers
20 views

Formulas for compressibility of solids (physics) [duplicate]

Possible Duplicate: Formulas for compressibility of solids I have a question which is technically a physics question, but since I have yet to find a good physics forum which accepts Latex, ...
2
votes
2answers
769 views

Lever Mechanics - How to formulate an ideal lever launch

Let's say I have a simple lever as shown below, and the lever is massless and the pivot is frictionless and there is no air resistance. I'm thinking the cradle for the projectile would have to have a ...
0
votes
1answer
86 views

Modeling falling spheres

The following situation interests me and I was wondering if there is software to model it? A large set of n spheres of uniform density and discrete sizes, mass proportional to volume, are dropped ...
4
votes
2answers
2k views

Where does the lost energy go in a rubber band powering a rotating shaft?

Okay, I'm no physics whiz, and this has me stumped. You know those toy airplanes you can get with the rubber-band driven propellers? You twist the propeller a bunch of times, and this stores ...
4
votes
1answer
427 views

speed of sound and the potential energy of an ideal gas; Goldstein derivation

I am looking the derivation of the speed of sound in Goldstein's Classical Mechanics (sec. 11-3, pp. 356-358, 1st ed). In order to write down the Lagrangian, he needs the kinetic and potential ...
3
votes
4answers
425 views

Complete set of observables in classical mechanics

I'm reading "Symplectic geometry and geometric quantization" by Matthias Blau and he introduces a complete set of observables for the classical case: The functions $q^k$ and $p_l$ form a complete ...
2
votes
2answers
3k views

degree of freedom of a rigid body 5 or 6?

I'm confused here. I have a three particle (rigid) system. What would be the degree of freedom? I found out five. 3 coordinates for center of mass and 2 for describing orientation. But we have only ...
3
votes
1answer
597 views

Rotating/Translating Disk

I was trying to understand an aspect of rotational dynamics and thought of a problem to help me learn. I'm sure this problem has been considered by countless people in the past, but I'm having some ...
2
votes
2answers
614 views

the difference between the operators between $\delta$ and $d$

In classical mechanics, when talking about the principle of virtual work, what is difference between $\delta r$ and $dr$? e.g. $W=\int \overrightarrow{F} \cdot \delta \overrightarrow{r} $ and ...
2
votes
3answers
567 views

Explanation for classic mechanics puzzle

I'm trying to figure out a nice way to describe to a kid the physics behind these experiments: Assuming ideal conditions, we have a small boat with a sale, close to a lake's shore and a fan fixed on ...
1
vote
1answer
110 views

Complex part of the solution for physical values

What's a physical meaning of, for example, complex part of the solution for coordinate change of the anharmonic oscillator? Why after substitute (for diff. equation solve) for real x we can earn $x = ...
0
votes
3answers
269 views

Classical mechanics. One-dimensional motion

Here is one task below. How to solve equation $$ m\ddot {x} + ax = F(t), x(0) = \dot x (0) = 0 $$ in quadratures by using two methods? I tried to create a system of equations $$ \begin{matrix} \dot ...
3
votes
1answer
152 views

Why is the $\langle v_{x}^{2} \rangle=\frac{1}{3} \langle v^2 \rangle$?

For a randomly moving particle. Or, I suppose that 1/3 could generalise to 1/n, where n is the non rotational degrees of freedom for that particle. Related reference Kinetic Theory of Gasses.
2
votes
0answers
360 views

include the stretch of the spring own weight in potential energy for spring pendulum?

we are given a problem with spring with its own mass $m$. I am confused how to set up the PE term in the Lagrangian. Assume the spring has length of $L_{0}$ when it is laying on a table horizontally. ...
1
vote
3answers
1k views

Stationary Solutions

An unbelievably basic question, but it's something I've never been taught. Am I right in thinking that the following defines a stationary solution? Let $\phi$ be some dynamical variable satisfying a ...
1
vote
1answer
2k views

Direction of friction on particle placed on a rotating turntable

If a particle is placed on a rotating turntable then the particle has a tendency to slip tangentially with respect to the underneath surface... So the friction should act tangentially to the ...
0
votes
2answers
26k views

Formula for a ball rolling down an Inclined Plane

Suppose we set up an experiment where we have an inclined ramp, and a spherical basketball. If we were to assume the ball to be perfectly round, and rolls down in a vertical manner and the situation ...
2
votes
2answers
1k views

What the difference between “orbital” and “orbit”?

What's the difference between "ortibal" and "orbit"? Which one should be used in physics? In quantum mechanics, is "atomic orbital" or "atomic orbit" used? And what about in classical mechanics? A ...
2
votes
4answers
1k views

Which angle causes an object to land quickest?

Say a canon is where the circle is, and it shoots two different canonballs at different angles, but at the same speed, which angle would make the cannonball hit the ground first? Intuitively I'd ...
0
votes
1answer
318 views

Parachute jumping (high altitude)

I heard about parachute jumping at an initial altitude of 30km. I want to simulate this flight numerically. How could I simulate the air drag (I mean, Which equation gives the air drag)? Normally I ...
1
vote
2answers
242 views

Is it easier to move or rotate an object? [closed]

This is a problem I'm facing on designing a moving bookcase for my home, I just don't have enough physics background to tackle the problem. Which of the following requires more force/effort? A ...
2
votes
1answer
106 views

state for a classical particle [duplicate]

Possible Duplicate: Why are coordinates and velocities sufficient to completely determine the state and determine the subsequent motion of a mechanical system? In classical mechanics, if ...
0
votes
0answers
22 views

How does a treadmill incline mechanism work? [duplicate]

Possible Duplicate: What's the difference between running up a hill and running up an inclined treadmill? I want to know how a system can give so many small steps of inclination and so ...
0
votes
2answers
4k views

When does not Newton's 3rd law apply?

Is Newton's 3rd law valid in non-inertial frames? If so, then are there other cases for which Newton's 3rd law is not applicable?
5
votes
3answers
1k views

Conservation of linear and angular momentum

Suppose I have two rigid bodies A and B and they are connected by a spring which is attached off-center (thus possibly causing torques). Due to the spring a force $f$ acts on A and a force $-f$ acts ...
0
votes
1answer
214 views

Horsepower achieved with multiple motors

Scenario I'm planning to build an electric motor for fun (not for any practical purpose). I recently purchased a shapeoko CNC mill kit and intend to manufacture most of the parts housing, stator etc. ...
3
votes
1answer
2k views

How do you know if a coordinate is cyclic if its generalized velocity is not present in the Lagrangian?

Goldstein's Classical Mechanics says that a cyclic coordinate is one that doesn't appear in the Lagrangian of the system, even though its generalized velocity may appear in it (emphasis mine). For ...
3
votes
1answer
214 views

In $\textbf{f} = -\boldsymbol{\nabla} u$, what is $u$?

I know that force is the negative gradient of the potential: $$\textbf{f} = -\boldsymbol{\nabla} u$$ where force $\textbf{f}$ is a vector and $u$ is a scalar. This is a relatively soft question, ...
0
votes
2answers
99 views

Can a mechanical systems on hold be switched off, in another way than just letting it do it's thing?

Can the value of the potential energy, which is responsible for driving the system, diminish in time, while the system itself is stationary during that time? Can there be dissipation in a system, ...
5
votes
1answer
696 views

Elementary derivation of the motion equations for an inverted pendulum on a cart

Consider a cart of mass $M$ constrained to move on the horizontal axis. A massless rod is attached to the midpoint of the cart, having a mass $m$ on its endpoint. See wikipedia for a picture and for a ...
2
votes
2answers
652 views

What is the significance of action?

What is the physical interpretation of $$ \int_{t_1}^{t_2} (T -V) dt $$ where, $T$ is Kinetic Energy and $V$ is potential energy. How does it give trajectory?
0
votes
2answers
240 views

Having Trouble With The Principle Of Conservation Of Momentum For a Multiparticle System

I'am reading John Taylor's Classical Mechanics chapter 1 page 20 where he proves the principle of conservation of momentum which states "If the net external force $F^{ext}$ on an $N$-particle system ...
4
votes
3answers
1k views

An example of non-Hamiltonian systems

I am preparing for the exam. And I need to know the answer to one question which I can't understand. "Give an example of non-Hamiltonian systems: in case of infinite number of particles; for a finite ...
2
votes
4answers
2k views

At same level do these two pipe lines give same pressure of water?

Provided that the two pipe lines are of same length, same material and in the same level, is the water pressure in both the layouts same or different? PS: In 1st pipeline the turns are not ...
8
votes
8answers
887 views

Is “Causality” the equivalent of a claim that the future is predictable based on the present and the past?

In classical (Newtonian) mechanics, every observer had the same past and the same future and if you had perfect knowledge about the current state of all particles in the universe, you could ...
4
votes
1answer
308 views

Entropy, flow of informations and fundamental theories

In the hierarchy of theories, first comes hamiltonian theory, from which one deduces kinetics theory, and at last thermodynamics and fluid theories. From a kinetics point of view, entropy and ...
0
votes
1answer
219 views

Finding the number of particles scattered by a certain angle

I'm trying to do the problem below, but it seems like there is incomplete information. PROBLEM STATEMENT: In a scattering experiment, $10^6$ $\alpha$ particles are scattered at an angle of ...
1
vote
1answer
216 views

On the Discretization of Energy Levels

We consider a system of "n" particles whose total energy E and net momentum $\vec{P}$ are fixed are fixed.There no net force on the system(assumed) $$\Sigma \epsilon_i= E$$ ...
16
votes
4answers
3k views

How does a car turn without any skidding?

The rear wheels of a car always face in the direction the car is moving. The front wheels are able to turn left or right and thus can point in the direction the car is moving towards. What I don't ...
14
votes
1answer
2k views

Why does a cuboid spin stably around two axes but not the third?

Let $C$ be a cuboid (rectangular parallelepiped) with edges of lengths $a < b < c$. Consider an axis that passes through the centers of two opposite faces of $C$. There are three such axes, ...
0
votes
2answers
1k views

Does effective potential for a gravitational force have a maximum below $E=0$?

The relevant figure is below (taken from Goldstein's Classical Mechanics). This figure plots the effective potential for a gravitational force. Does the effective potential $V'$ go flat below $E_2=0$? ...
4
votes
4answers
747 views

If a pendulum is on a rotating table, will a torque be generated?

Here is the set up. Very simple. A flat (i.e. horizontal table, there is no gravity) and rounded table that spins on its axis (through the center of the table). A spring mass system is now put on the ...
5
votes
2answers
265 views

Is it normal for physical functions to lack a 2nd derivative?

My question is about the appearance of a non-analytic function in the formula for the resistive force in air or other medium. Considering the 1-dimensional case as covered by Walter Lewin in his 8.01 ...
1
vote
3answers
132 views

How can one know if a theory allow action at a distance effects or not?

1-In general, if a theory has action at a distance effects, where can that appear exactly in the theory? 2-Does it appear in the dynamical law of the theory? (does it appear in Newton's 2nd law? ...
0
votes
1answer
75 views

Does reactive force require the two force involved have to have two different medium for reactive force to occur?

Does reactive force require the two force involved have to have two medium for reactive force to occur? I know the fuel-thruster is working on vacuum space, but we human could not use arm to swim in ...
0
votes
1answer
50 views

Is it possible to make use of paper/bill permeate by chemical compound to became a paper-made bullet-proof vest?

Is it possible to make use of paper/bill permeate by chemical compound to became a paper-made bullet-proof vest? This is inspired by Greece and Italy tend to have more riot than rest of the Europe ...
4
votes
2answers
489 views

Classical Limit of Commutator

In Dirac's book Principles of quantum mechanics (4th ed., pgs 87-88), he seems to give a very elementary argument as to how the commutator $[X,P]$ reduces to the Poisson brackets ${x,p}$ in the limit ...
5
votes
3answers
1k views

Classical Limit of Schrodinger Equation

There is a well-known argument that if we write the wavefunction as $\psi = A \exp(iS/\hbar)$, where $A$ and $S$ are real, and substitute this into the Schrodinger equation and take the limit $h \to ...