General questions about the way objects move and interact. This tag should be used when the tags for certain kinds of mechanics (newtonian-mechanics, classical-mechanics, quantum-mechanics, etc.) are too specific.
6
votes
8answers
4k views
Which Mechanics book is the best for beginner in math major?
I'm a bachelor student majoring in math, and pretty interested in physics. I would like a book to study for classical mechanics, that will prepare me to work through Goldstein's Classical Mechanics. ...
10
votes
4answers
1k views
What's the difference between running up a hill and running up an inclined treadmill?
Clearly there will be differences like air resistance; I'm not interested in that. It seems like you're working against gravity when you're actually running in a way that you're not if you're on a ...
6
votes
9answers
2k views
Book about classical mechanics
I am looking for a book about "advanced" classical mechanics. By advanced I mean a book considering directly Lagrangian and Hamiltonian formulation, and also providing a firm basis in the geometrical ...
2
votes
1answer
204 views
What variables does the action $S$ depend on?
Action is defined as,
$$S ~=~ \int L(q, q', t) dt,$$
but my question is what variables does $S$ depend on?
Is $S = S(q, t)$ or $S = S(q, q', t)$ where $q' := \frac{dq}{dt}$?
In ...
0
votes
1answer
706 views
Speed of a fly inside a car
A couple of weeks ago I was travelling in a car (120 km/h approximately) and I saw a fly flying in front of me (inside the car, near my nose, windows closed). I wonder how was that possible.
Does it ...
13
votes
6answers
5k views
What is the difference between Newtonian and Lagrangian mechanics in a nutshell?
What is Lagrangian mechanics, and what's the difference compared to Newtonian mechanics? I'm a mathematician/computer scientist, not a physicist, so I'm kind of looking for something like the ...
3
votes
2answers
348 views
Bernoulli's equation and reference frames
So I was thinking about this while driving home the other day.
I've never been quite clear on why when you drive with the windows down air rushes into your car. I thought this might be explained by ...
2
votes
3answers
2k views
Torque vs Moment
I was wondering, why in Newtonian physics torque is called "torque" while in static mechanics they call it "moment"?
I prefer by far the term "torque", for not only it sounds strong, but also ...
0
votes
3answers
2k views
Convert running speed uphill to equivilent speed on flat
Given a certain running pace uphill, I want to be able to determine an equivalent pace running with no elevation change. Assumptions: similar effort in both cases (say for example running at 90% max ...
4
votes
4answers
489 views
Are the physical laws scale-dependent?
If you read the article "More Is Different", by P.W. Anderson (Science, 4 August 1972), you will find a deep question: are the physical laws dependent of the size of the system under study?
As an ...
8
votes
2answers
2k views
Why can't a piece of paper (of non-zero thickness) be folded more than “n” times?
Updated:
"In order to fold anything in half, it must be π times longer than its thickness, and that depending on how something is folded, the amount its length ...
1
vote
6answers
1k views
What will happen if a plane trys to take off whilst on a treadmill?
So this has puzzled me for many a year... I still am no closer to coming to a conclusion, after many arguments that is. I don't think it can, others 100% think it will.
If you have a plane trying to ...
4
votes
3answers
644 views
Why does the cart move? [duplicate]
A while ago someone proposed the following thought experiment to me:
A horse attached to a cart is resting on a horizontal road. If the horse attempts to move by pulling the cart, according to the ...
2
votes
1answer
419 views
Force on rope with accelerating mass on pulley
I have a pretty basic pulley problem where I lack the right start.
A child sits on a seat which is held by a rope going to a cable roll (attached to a tree) and back into the kid's hands.
When it ...
1
vote
1answer
361 views
Classical Mechanics for Mathematician [duplicate]
Possible Duplicate:
Which Mechanics book is the best for beginner in math major?
I am looking for suitable ways to learn mechanics in mathematician's perspective.
I went through:
...
3
votes
2answers
278 views
How did L.H. Thomas derive his 1927 expressions for an electron with an axis?
I'm looking at the 1927 paper of Thomas, The Kinematics of an Electron with an Axis, where he shows that the instantaneous co-moving frame of an accelerating electron rotates and moves with some ...
1
vote
1answer
83 views
How to find the value of the parameter $a$ in this transfer function?
I am given a transfer function of a second-order system as:
$$G(s)=\frac{a}{s^{2}+4s+a}$$
and I need to find the value of the parameter $a$ that will make the damping coefficient $\zeta=.7$. I am not ...
1
vote
0answers
123 views
Conveyor scales modeling
Assume we have a conveyor scales. Which consists of scales, and motor with conveyor belt placed above, so that the boxes can be measured (weight) while moving above. What I want is to create the model ...
0
votes
1answer
274 views
Stacking gold Bars
I once heard that because gold is so malleable, while also being very heavy; that if one were to stack several layers of bars on top of on another (like is so familiarly depicted in movies & TV), ...
26
votes
10answers
2k views
Mechanics around a rail tank wagon
Some time ago I came across a problem which might be of interest to the physics.se, I think. The problem sounds like a homework problem, but I think it is not trivial (i am still thinking about it):
...
25
votes
4answers
9k views
What are the precise statements by Shouryya Ray of particle dynamics problems posed by Newton which this news article claims have been solved?
This recent news article (here is the original, in German) says that
Shouryya Ray, who moved to Germany from India with his family at the age of 12, has baffled scientists and mathematicians by ...
19
votes
9answers
6k views
How did Newton discover his second law?
I've always assumed/been told that Newton's 2nd law is an empirical law — it must be discovered by experiment. If this is the case, what experiments did Newton do to discover this? Is it related to ...
8
votes
2answers
222 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 ...
5
votes
1answer
154 views
Why can you assume that the angular momentum vector of a top will always track its axis of rotation?
My favorite physics 101 textbook (Giancoli) explains precession in terms of a spinning top whose axis is tilted from the vertical.
The way the book sets things up, $L$ (angular momentum) points along ...
6
votes
2answers
378 views
What is the highest energy position for a double pendulum? And for which energy positions is it chaotic?
Math/physics teachers love to break out the double pendulum as an example of chaotic motion that is very sensitive to initial conditions. I have some questions about specific properties:
For a ...
1
vote
3answers
791 views
Direction of torque precession of a spinning wheel
Consider a spinning wheel, which is held up by one end of it's axis like this:
To explain why the change of angular momentum is directed as shown in the figure above, one usually says that there is ...
7
votes
1answer
503 views
Coriolis force and Newton's third law
I would like to ask a stupid question here.
If a body 'b' moving downward with a velocity v in a rotating frame of reference with angular velocity w, and w and v not being parallel and anti parallel. ...
5
votes
2answers
269 views
Will a wave packet undergo dispersion when traveling down a hanging rope?
Suppose I tie one end of a rope to my ceiling and the other end to a spot on my floor directly underneath it. Because the rope has some mass, the tension varies along the rope, from highest at the ...
5
votes
1answer
457 views
Equilibrium and movement of a cylinder with asymmetric mass centre on an inclined plane
A cylinder whose cross section is represented below is placed on an inclined plane. I would like to determine the maximum slope of the inclined plane so that the cylinder does not roll. The mass ...
4
votes
3answers
148 views
Does more rain strike a vehicle while moving or while stopped (or neither)? [duplicate]
Assume there is a rainstorm, and the rain falling over the entire subject area is perfectly, uniformly distributed. Now assume there are two identical cars in this area. One is standing still, and ...
4
votes
2answers
1k views
Shape of Fan Blades
How is the shape of the blades of an air fan determined? Trial and error, or is there a theory behind it? What are they trying to maximize, volume of air dislocated per rotation?
0
votes
3answers
675 views
4th equation of motion
Ive been given the 4 equations of motions The fourth being:
$$s=ut+\frac{1}{2}at^2$$
If rearranged it forms the quadratic equation
$$at^2+2ut-2s=0$$
But that means that t has 2 values.
Will ...
7
votes
1answer
169 views
Why does vibration loosen screws?
I am trying to figure out why vibrations (say, from an engine) loosen screws. It seems to me that there is evident symmetry between loosening and tightening a screw. I am wondering what breaks this ...
6
votes
1answer
158 views
Can a deformable object “swim” in curved space-time? [duplicate]
Possible Duplicate:
Swimming in Spacetime - apparent conserved quantity violation
It is well known that a deformable object can perform a finite rotation in space by performing deformations ...
5
votes
1answer
135 views
Distance a curveball travels?
I've seen some discussions regarding the movement of a spinning object, say a curveball. However, all have been largely qualitative. I was wondering if anyone has seen or worked through a ...
5
votes
2answers
337 views
What are the normal modes of a vertical rope?
Closely related to this question on traveling waves on a hanging rope, I would also like to know what the normal modes are on a rope that hangs vertically, fixed at both ends.
Tension in the rope ...
2
votes
2answers
202 views
What sustains a rigid body's rotation at its constant angular(rotational) speed?
Continuing from the following scenario from my previous question Centripetal force of a rotating rigid body? :
Consider someone pushing a roundabout in a playground. Initially the
roundabout is ...
2
votes
2answers
520 views
Stress vs Strain for mild steel
After Yield point on stress strain diagram the under curve occurs what does it mean what will happen for the mild steel at that particular time and again why the curve goes to up and reaches ...
2
votes
7answers
2k views
What are the Constraints on Building a Tower to Space?
When I was a boy I used to daydream about building a tower so tall that the top of it would stick out of the top of Earth's atmosphere project into near space.
There would perhaps be a zero gravity ...
1
vote
2answers
179 views
Numerical torque calculation
Suppose I can compute interaction energy of two rigid bodies as a function of their coordinates of centers of masses and Euler rotation angles (total 6 + 6 degrees of freedom). Now I can numerically ...
1
vote
2answers
420 views
Spinning bucket of water in zero gravity
Everyone knows how the surface of a spinning bucket of water would look like on earth - parabolic. But what if we turned off gravity (for instance by doing the experiment in a freely falling lift)? ...
1
vote
3answers
5k views
What is the difference between a moment and a couple?
In mechanical engineering, the torque due to a couple is given by $\tau = P\times d$, where $\tau$ is the resulting couple, $P~$ is one of the force vectors in the couple and $d$ is the arm of the ...
0
votes
2answers
105 views
sending information over a wire--mechanically [duplicate]
Possible Duplicate:
Is it possible for information to be transmitted faster than light?
I've thought about this since I was a little kid. I know it isn't exactly feasible, but it still ...
0
votes
2answers
1k views
Work done by spring over distance
I'm working through a problem involving energy conservation. Unfortunately, I cannot calculate the work done by a spring.
...
-1
votes
1answer
87 views
Confusions about rotational dynamics and centripetal force
I am a high school student. I am having confusions about the centripetal force and rotational motion . I have known that a body will be in rest or in uniform velocity if any force is not applied. But ...
