All Questions
57
questions
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19
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2d elastic scattering with an impact parameter
Hello guys I have homework that has tasked me with connecting the effect of the scattering parameter to the energy transfer in a 2d elastic collision of two arbitrary spheres with one of them standing ...
- 1
1
vote
1
answer
49
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How do physicists determine where to place the world or inertial frame when describing the equation of motion of an object?
For example, I have a pendulum as shown in the diagram above. I would like to write down its equation of motion. To do this, I must define a world frame (or inertial frame, or origin).
But this is ...
- 320
5
votes
5
answers
2k
views
Why is the centre of mass useful in a discrete particle system?
How does the concept of center of mass apply to discrete particle systems with varying masses and motions, especially when dealing with a large number of particles?
Considering the challenge of ...
- 91
1
vote
4
answers
220
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Reference frame doubts about isotropy
Landau & Lifshitz on p.5 in their "Mechanics" book states the following:
...a frame of reference can always be chosen in which space is
homogeneous and isotropic and time is homogeneous....
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0
answers
14
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Reading on weighing scales at the equator of a moon in a tidally locked two-body system
I'm trying a made-up extension of this problem. Consider the planet Mars and its moon Deimos, which can be approximated as meeting the following simplifying conditions:
Both objects are perfect ...
- 208
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votes
2
answers
119
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Question about velocities in different reference frames
Suppose $\hat{x^{'}}, \hat{y^{'}}, \hat{z^{'}} $ are the unit vectors of an inertial frame and $\hat{x}, \hat{y}, \hat{z} $ are the unit vectors of a frame which maybe accelerating, rotating, whatever....
- 430
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votes
1
answer
70
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Doubt in fictitious forces chapter in Morin
The question is this -
I know 2 is what the non-inertial frame measures, but isn't $\frac{d\mathbf{A}}{dt}$ the real thing, the physical thing? And you can write that too in terms of the unit vectors ...
- 430
-4
votes
3
answers
391
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What is the velocity of centre of mass in centre of mass frame?
Velocity of centre of mass in centre of mass frame is considered zero. But how are the two contradictory statements written in the book?
- 57
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votes
4
answers
2k
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Why is a reference frame moving with constant velocity with respect to an inertial frame also inertial?
We define an inertial frame, as a frame of reference where:
Newton's 1st law holds.
It is then stated that a reference frame moving with constant velocity with respect to an inertial frame is also ...
- 1,648
0
votes
1
answer
241
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Rotating reference frame - Taylor Problem 1.27 [closed]
I'm having trouble understanding how to think about Problem 1.27 in Taylor's Classical Mechanics. I want to be able to solve similar problems qualitatively when it comes to changing reference frame so ...
- 177
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votes
2
answers
115
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When to apply $I_c \underline{\omega} = \underline{M_c}$?
I was solving an exercise the other day, about a rolling cylinder on an inclined plane. Initially the cylinder slides, but then it begins to roll and the problem wanted to know the velocity of the ...
- 402
4
votes
1
answer
61
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Moving body is collided with a spring system.Why there is a difference in maximum compressed distance for different observers?
Suppose a body of mass m moving with velocity collides with a spring system.The event is being observed by two observers, one at rest and one moving with a velocity v opposite direction to that of the ...
- 538
0
votes
1
answer
64
views
Find the equation for the angle $\theta$ in which the particle leaves the semicircle. No Friction [closed]
I think I missed something in this mechanics problem.
We're given a polished (no friction) and homogeneous hemicircle which has mass $M$ and a particle of mass $m$ laying on the top of it.
There is ...
- 153
1
vote
2
answers
264
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Finding latitude of landing of projectile in Rotating Earth
Assuming that the Earth is a uniform sphere of radius $R$, rotating about its axis with a uniform angular velocity $\omega$. A rocket is launched from the Equator in a direction due North. If it keeps ...
- 23
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votes
1
answer
126
views
Using reduced mass to solve problems
A small block of mass $m$ rests on the bottom of a big box also of mass $m$. If the small block is then given a velocity $V$ to the right, how far has the box moved once the block has come to rest ...
- 67
2
votes
2
answers
77
views
Total force needed to maintain constant acceleration of a bus
Suppose there is a person wearing roller-skates, inside a bus ( to neglect the friction on the floor ). The mass of this person is $m$ and the mass of the bus $M$.
Suppose, the bus now starts to ...
- 493
0
votes
1
answer
420
views
Kinetic Energy of pendulum with moving support
I am trying to calculate the kinetic energy of a pendulum with moving support. I have come across two ways that could be used to calculate the kinetic energy, and although I know that the first of ...
- 29
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votes
1
answer
58
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Dummy variables and Galilean Invariance
I've faced a small doubt, and I was hoping someone could verify this for me.
According to Galilean transformation, consider $2$ frames - $S_1$ and $S_2$ moving relative to each other. $S_1$ is at rest,...
- 1,791
2
votes
5
answers
339
views
Is "non-inertial" frame a relative term?
I've heard only two definitions of non-inertial frame so far:
I. A frame that is accelerating with respect to an inertial frame.
II. A frame where Newton's Laws are invalid.
Let's begin with ...
- 89
-3
votes
2
answers
117
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Acceleration of the center of mass without external forces paradox
From classical physics we know that the acceleration of the center of mass of an object is zero if there is no external forces.
Can someone tell me what's wrong with this counter example:
Counter ...
- 7
1
vote
1
answer
131
views
Newton's 1st law, applied in a manifold
A seemingly interesting question.
Newton's 1st law states that objects continue in straight lines, unless acted upon by external forces. Now consider a frictionless manifold. Since it is locally ...
- 428
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votes
1
answer
209
views
Will the plane of oscillation of a pendulum change if I rotate the suspension point
I'm having trouble understanding Foucault pendulum and from that I've extracted one of my doubt and here it goes:
A pendulum on a fixed platform is shown
Now if we rotate the platform as shown
Will ...
- 1,270
1
vote
1
answer
130
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Problem regarding equations in different frame of reference
Previously I asked this question and got the following answer.
I'm asking for reason why you can split Tension(first case) but not mg(second case)
When you say 'splitting,' you really mean ...
- 195
3
votes
0
answers
98
views
Path of a bead on a rod with external torque [closed]
Imagine a bead, free to move along the length of a horizontal rod, pivoted at one end. The system is initially at rest, with the bead at some distance from the end. Now, a constant torque is applied ...
- 1,076
0
votes
2
answers
182
views
Relating torque and time rate of change of angular moment when an object isn't rotating about its center of mass [duplicate]
My book "Fundamentals of Physics" by Halliday, Resnick, Walker says:
The net external torque acting on a system of particles is equal to the time rate of change of the system's total ...
- 105
8
votes
9
answers
2k
views
Different coordinate system as opposed to different reference frame
I'm having a hard time getting the difference between the two. In Euler's equations of rotating bodies for example, we have:
$$ \mathbf{\dot{L}}+\mathbf{\omega} \times \mathbf{L} = \mathbf{\Gamma},$$
...
- 1,038
3
votes
2
answers
2k
views
Why does a body not rotate if force is applied on the centre of mass?
The definition of centre of mass on Wikipedia is given as
This is the point to which a force may be applied to cause a linear acceleration without an angular acceleration.
How can I prove that such ...
- 517
0
votes
1
answer
101
views
Why does the amplitude of a pendulum increases when continuously changing the rope length? [duplicate]
The simplistic answer is that I'm pumping energy into the system thus the velocity increases and so is the amplitude.
I'm more interested in understanding it from forces considerations.
- 11
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votes
3
answers
1k
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Are there any cases in classical mechanics in which Newton's second law fails?
I am asking if there is any case in classical i.e., non-quantum, mechanics in which one cannot use Newton's second law $$\sum \mathbf{F}=\frac{\mathrm{d} \mathbf{p}}{\mathrm{d} t},$$ to find the ...
- 1,092
3
votes
2
answers
934
views
Rotating Rod As a conical pendulum
Consider A Rigid Rod hinged at its top point Whirled around in a circle (similar to a conical pendulum). It is given that the angular velocity (and thus the semi-vertical angle) is constant. I am ...
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