In introductory mechanics, the momentum of a particle is its mass times its velocity. In electrodynamics, the momentum of a field is proportional to the cross-product of the electric field with the magnetic field. In special relativity, momentum is generalized to four-momentum.
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A thought on definition of momentum
Well, this is a simple, basic and I think even silly doubt. The first time I saw the definition of momentum as $p = mv$ I started to think why this is a good definition. So I've read the beginning of ...
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2answers
898 views
Do the physics in the FlyBoard video make sense?
If you haven't seen the video of the FlyBoard, please have a look: http://www.youtube.com/watch?v=Cd6C1vIyQ3w&feature=youtube_gdata_player
Yes, it's amazing, but do the physics make sense or is ...
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4answers
170 views
Can a balloon be used as an anchor point for a pulley?
For a physics/ engineering contest, I want to use a large balloon as an anchor point for a pulley. This would allow me to raise and drop masses.
However, in testing, when I pull on the pulley the ...
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2answers
101 views
Do photons actually generate a slight kinetic force?
My question is even though photons have no (rest) mass, do they emit a external force due to EM radiation causing electrons to be excited and jump to higher energy shells which electrons have mass ...
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1answer
318 views
Elastic Collision And Momentum
The question I am working on is, "Two blocks are free to slide along the friction-less wooden track shown below. The block of mass $m_1 = 4.98~kg$ is released from the position shown, at height $h = ...
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1answer
75 views
Can electromagnetic momentum be introduced at pre-university level as for electromagnetic energy?
Electromagnetic energy is introduced at pre-university level, starting with static electric energy followed by static magnetic energy. But the introduction of electromagnetic momentum usually has to ...
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0answers
48 views
A 0.1kg ball of dough is thrown up with a velocity of 15m/s. What is the momentum halfway up? [closed]
I know that $p=mv$ and (0.1kg)(15m/s)=1.5 kg m/s and the momentum at the vertex is 0, but what is the momentum halfway up?
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3answers
357 views
What is the difference between impulse and momentum?
What is the difference between impulse and momentum?
The question says it all...I know the second of of them is mass * velocity, but what is the first one for, and when is it used? Also, what are its ...
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1answer
79 views
Combining Conservation Laws ~ Homework Problem Guidance
Problem 8.79 - Combining Conservation Laws
A 5.00-kg chunk of ice is sliding at 12.0 m/s on the floor of an ice-covered valley when it collides with and sticks to another 5.00-kg chunk of ice that is ...
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1answer
144 views
What happens if object is thrown in empty space?
If I throw a object in empty space, I apply a force to throw that.
Then it gains some acceleration and it's speed increases.
So will it's speed keep on increasing, or it will get stable?
If yes, ...
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1answer
65 views
What is the momentum of these emitted photons?
5 x 10^7 kg of radioactive material emits energy in the form of photons of red light (700 nm). (Note: photons have no mass.)
What is the momentum of each photon?
...
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1answer
55 views
Mean value of the force in a collision problem
I have the following problem:
A point with mass $m$ and speed $v$ collides with a fixed obstacle and penetrates it, stopping in a space $\Delta x$. Calculate $\Delta t $.
I understand the way my ...
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2answers
224 views
Small car colliding with large truck
A small car collides with a large truck. Why do both vehicles experience the same magnitude of force? Wouldn't the large vehicle experience less force than the small one?
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1answer
146 views
Impulse from absorbing a photon? Is there an increase in rest mass?
I'm going through A P French's special relativity. In one chapter (6) the following is set up:
Suppose that a stationary particle of mass $M_0$ is struck by a photon of energy $Q$, which is ...
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1answer
71 views
How to get the new direction of 2 disks colliding?
I'm developing a 2D game including collisions between many disks. I would like to know how I can get the angle corresponding to the new direction of each disk.
For every disk I have this information ...
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2answers
104 views
Is air drag equation in term of momentum still valid?
This is the known equation of air drag:
$$m{\bf a}=mg-\mathcal D=mg-b{\bf v}.$$
Considering this, is air drag equation in term of momentum still valid?
$$m{\bf v}=mv_g-b{\bf r}.$$
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9answers
853 views
How to explain independence of momentum and energy conservation in elementary terms?
I'm trying to explain to someone learning elementary physics (16 year old) that linear momentum and energy are conserved independently. I'm not a professional physicist and haven't tried to explain ...
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2answers
105 views
Does spacetime have momentum?
In what sense can it be said that spacetime possesses momentum? Can an experiment be envisaged to test this question?
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1answer
217 views
End position of movement factoring in deceleration
Ok I am hoping to apply this answer to a piece of software, but it uses physics to work out the result so I require some help in that department.
I will attempt to explain this the best I can.
I ...
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1answer
67 views
particle accelerator in space
I'm attempting to learn special relativity and i'm having trouble calculating velocity and momentum for each part of the system after interactions.
I wanted to know how fast a linear accelerator and ...
3
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2answers
311 views
block slides on smooth triangular wedge kept on smooth floor.Find velocity of wedge when block reaches bottom
Find the velocity of the triangular block when the small block reaches the bottom:
Here is what I did:
The final velocity(at the bottom)of the small block of mass m is $\sqrt{2gh}$ along the plane ...
3
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3answers
175 views
Proof for $p=\gamma_Pmu$
As I'm reading about Relativistic Momentum, my book states the following:
$$p=m \frac{\Delta x}{\Delta t}=m\frac{\Delta x}{\sqrt{(1-u^2/c^2)}\Delta t}=\frac{mu}{\sqrt{1-u^2/c^2}}=\gamma_Pmu$$
...
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4answers
600 views
Intuitive explanation of why momentum is the Fourier transform variable of position?
Does anyone have a (semi-)intuitive explanation of why momentum is the Fourier transform variable of position?
(By semi-intuitive I mean, I already have intuition on Fourier transform between ...
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2answers
224 views
Translation Invariance without Momentum Conservation?
Instead of the actual gravitational force, in which the two masses enter symmetrically, consider something like $$\vec F_{ab} = G\frac{m_a m_b^2}{|\vec r_a - \vec r_b|^2}\hat r_{ab}$$ where $\vec ...
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1answer
155 views
What is the result of a classical collision between THREE point particles at the same precise instant?
Classical Mechanics is said to be deterministic, a statement that nearly always is followed by that quote from Laplace, something like
If at one time, one knew the positions and velocities of all ...
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3answers
175 views
Simple elastic collision
If a particle with mass $m$ collides with a wall at right angles, and the collision is perfectly elastic. The particle hits the wall at $v\ ms^{-1}$. There is no friction or gravity.
So the particle ...
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2answers
199 views
Can conservation of momentum related to Newton's first law?
I know this is a scrap of thought, but the first law states that (from Wikipedia):
If an object experiences no net force, then its velocity is constant
Is it describing the conservation of ...
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1answer
251 views
Is momentum conservation for the classical Schrödinger equation due to non-relativistic or due to some more exotic invariance?
I had no problem appliying the Neothers theorem for translations to the non-relativistic Schrödinger equation
$\mathrm i\hbar\frac{\partial}{\partial t}\psi(\mathbf{r},t) \;=\; \left(- ...
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3answers
258 views
Lorentz force in Dirac theory and its classical limit
It is well known that in Dirac theory the time derivative of $P_i=p_i+A_i$ operator (where $p_i=∂/∂_i$, $A_i$ - EM field vector potential) is an analogue of the Lorentz force:
$\frac{dP_i}{dt} = ...
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4answers
742 views
Is it possible to lift yourself off from the ground?
Say for instance a person who was strong enough to lift double his body weight. If he placed his hands under his bottom and tried to lift$^1$ himself$^2$ off the ground, could he?
--
$^1$In a ...
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2answers
5k views
What is the relationship between kinetic energy and momentum?
I can't seem to figure out the relationship between $E_k$ and $p$ or $F$.
I understand that the units are pretty different. But for example:
A bullet with a mass of 10.0g is moving at the speed of ...
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3answers
169 views
Classical mechanics and the speed of a train-mosquito collision, when perfectly rigid bodies
This is all under the assumption that they are perfectly rigid bodies:
A train is moving at 300m/s.
A mosquito is moving directly towards it, head-on, at 4m/s.
When the mosquito and the train ...
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4answers
179 views
Find total energy and momentum of an moving electron in a rest frame
I have an electron moving with speed $u'$ in a frame $S'$ moving with speed $v'$ relative to a rest frame $S$.
How do I find the total energy and momentum of the electron in the rest frame $S$?
I ...
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1answer
152 views
4-momentum and an $y$ component of momentum
I have 2 coordinate systems which move along $x,x'$ axis.
I have derived a Lorentz transformation for an $x$ component of momentum, which is one part of an 4-momentum vector $p_\mu$. This is my ...
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1answer
406 views
Elastic collision in two dimensions
Suppose a particle with mass $m_1$ and speed $v_{1i}$ undergoes an elastic collision with stationary particle of mass $m_2$. After the collision, particle of mass $m_1$ moves with speed $v_{1f}$ in a ...
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0answers
135 views
Early stages of a computational model for object movement charting
We would like to build a computational model capable of accurately predicting the position of any object inside a chamber at any given time.
Inside the model we would have a number of smaller ...
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3answers
130 views
Displacement with zero velocity
I know that we can rotate a deformable object using internal forces only in space. Thus we can cause an angular displacement without the use of any external forces.
The following youtube video shows ...
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0answers
66 views
about wavefunction and vector entries
I am beginer of physics and I am studying some very fundamental idea of quantum mechanics by myself. In the introducing book I am reading, there is an example to show a particle diffraced by a slit or ...
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2answers
184 views
Why is the “canonical momentum” for the Dirac equation not defined in terms of the “gauge covariant derivative”?
The canonical momentum is always used to add an EM field to the Schrödinger/Pauli/Dirac equations. Why does one not use the gauge covariant derivative? As far as I can see, the difference is a factor ...
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2answers
105 views
Directionality of angular momentum
I was told that the sum of linear and angular momentum is conserved.
Given that angular momentum's direction as a vector is completely arbitrary (I believe there is no physical reason for choosing ...
3
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4answers
386 views
Is the momentum operator well-defined in the basis of standing waves?
Suppose I want to describe an arbitrary state of a quantum particle in a box of side $L$. The relevant eigenmodes are those of standing waves, namely
$$ \left<x|n\right>=\sqrt{\frac{2}{L}}\cdot ...
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2answers
243 views
Intuitively Understanding Work and Energy
It is easy to understand the concepts of momentum and impulse. The formula $mv$ is simple, and easy to reason about. It has an obvious symmetry to it.
The same cannot be said for kinetic energy, ...
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0answers
81 views
A momentum problem [closed]
A 3.0 kg car A travelling 8.5m/s on a frictionless track collides and sticks on to a stationary 2.0 kg car B.
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1answer
83 views
Spring coupled platforms & conservation of momentum - can it be solved with freshman physics?
This question came up as an exercise in a first year undergraduate course I was a TA for. It turned out to be a lot more difficult (impossible?) than anticipated...
Two platforms of mass $M_1$ and ...
3
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2answers
154 views
Does the canonical commutation relation fix the form of the momentum operator?
For one dimensional quantum mechanics $$[\hat{x},\hat{p}]=i\hbar $$
Does this fix univocally the form of the $\hat{p}$ operator? My bet is no because $\hat{p}$ actually depends if we are on ...
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3answers
928 views
Why is force described as rate of change of momentum?
momentum = mass * velocity
Differentiating both sides leads to
force = mass * acceleration
since the mass doesn't participate in the differentiation as it is constant.
Is this a sound ...
3
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2answers
909 views
Momentum-Representations in Quantum Mechanics
Why do we get information about position and momentum when we go to different representations. Why is momentum, which was related to time derivative of position in classical physics, now in QM just a ...
3
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1answer
305 views
Momentum as Generator of Translations
I understand from some studies in mathematics, that the generator of translations is given by the operator $\frac{d}{dx}$.
Similarly, I know from quantum mechanics that the momentum operator is ...
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1answer
99 views
Integration of constant: $\int dp = \Delta p$ in impulse formula
In University Physics, it has something like:
$$\int \sum F dt = \int \frac{dp}{dt} dt = \int dp = \underbrace{p_2 - p_1}_{\Delta p?}$$
But I thought $\int dp = p$? Though my maths is really rusty ...
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0answers
26 views
Elastic Collision Between Two Objects [duplicate]
Possible Duplicate:
Elastic Collision And Momentum
I've already asked this question, Elastic Collision And Momentum, but I didn't find the answer particularly helpful--sorry, I don't mean ...
