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.
0
votes
1answer
128 views
Is pressure distribution affected by shape
We have two iron (assume real-life stiffness) manhole covers resting on friction-less, perfectly smooth shims on flat ground. One is circular and the other square.
If a force F is applied vertically ...
2
votes
3answers
657 views
Initial vs Constant Orbital Velocity
I am working on some basic physics simulation for a game and need to simulate gravity. I have a system working that is behaving more or less correctly so far, but I want to see if I can send a ...
0
votes
1answer
78 views
Explain moving lightbulb [closed]
An acquaintance of mine, while being home alone, saw that the light bulb in the room which was hanging from the ceiling with wires having a pendulum motion which was more than noticeable. He says that ...
6
votes
2answers
255 views
How does the distance between two rails effect the speed of a steel ball bearing?
As part of a school science project, I constructed a Rollercoaster using Polyurethane tubing as rails for a steel ball bearing to rest on. In the process of building the coaster I observed that ...
0
votes
0answers
460 views
Physics tension question [closed]
Two blocks are pulled across a frictionless surface by a $240\ N$ force, as shown in the diagram below: $60\ kg$ - - - cord - - - $20\ kg$ → $240\ N$. If the blocks are accelerating at $3\ m/s^2$ what ...
2
votes
0answers
75 views
Surface normal on the earth to the sun at a given point in time
How complicated is it to calculate a surface normal on the spherical approximation of the earths surface pointing towards the sun at a given point in time?
What I try do is to highlight a small area ...
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 ...
0
votes
0answers
281 views
Calculating torque of actuators? [closed]
How do you calculate the torque of a brushless dc electric motor?
How do you calculate the torque of a hydraulic motor?
How do you calculate the push and pull force of a double acting hydraulic ...
3
votes
1answer
518 views
Integrals of Motion
Landau writes in chapter 2 of his Mechanics book "The number of independent integrals of motion for a closed mechanical system with s degrees of freedom is 2s-1". Then he goes on to show how -- "Since ...
2
votes
2answers
462 views
Does the phase space (configuration and momentum space) of particles have a Euclidean norm? Does it have a useful meaning of “distance”?
Often in engineering physics, different vector spaces are used to visualize the trajectories (evolution) of systems. An example being the 6n dimensional phase space of n particles. It is not very ...
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 ...
2
votes
1answer
499 views
Does decoherence explain all instances of wave function collapse?
Specifically, how can decoherence explain the appearance of flecks of metallic silver on a photographic plate when exposed to the very weak light of a distant star?
EDIT: Perhaps the advocates of ...
3
votes
1answer
179 views
Coincidence detectors in Bell tests: How close is close enough?
When is a coincidence a coincidence? We know that to identify entangled photons, the electronics is set to look for simultaneous clicks at opposite detectors. The size of the window is to some degree ...
7
votes
3answers
1k views
How do you produce electricity from a wind mill?
How does a spinning windmill produce electricity?What is the principle behind the windmill?
0
votes
0answers
222 views
Which actuator is more effective: pneumatic, hydraulic, or electric? [closed]
For an system that amplifies strength by about two (press capacity of 400 lbs.), which would be the most practical, or the most compact?
A pneumatic system that uses air cylinders or air muscles,
A ...
0
votes
2answers
171 views
How could pinion in automatic quartz watch be rotated at 100K RPM?
Wikipedia article on automatic quartz watch describes the watch mechanism as follows: a rotating pendulum is attached to a pinion and when the wearer moves his hand the pinion is rotated at up to 100 ...
2
votes
2answers
362 views
Wave equations & propagation theories
I'm interrested in making computer simulation but I've run into rather physics oriented problem. I have to choose how to propagate my wave. Though I've found technique called FDTD (finite-difference ...
2
votes
2answers
519 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 ...
1
vote
2answers
280 views
What, if anything, makes forces the “cause” and acceleration the “effect”? [closed]
We typically say that forces cause acceleration inversely proportionate to mass. Would it be any less correct to say that acceleration causes forces proportionate to mass? Why?
(Note that the ...
2
votes
0answers
141 views
Displacement due to sinusoidal load on a finite strip in an infinite plane
From a paper on tunnel design I've been reading: (http://www.sciencedirect.com/science/article/pii/0886779887900113)
In the present application, the solu-
tion corresponding to a sinusoidal load
...
2
votes
2answers
265 views
a question on Lagrange's equation when the time derivative of the generalized co-ordinates is constant
Consider a system whose generalized co-ordinates are $q_i$ and is under the constraints $\dot{q_i} = K_i \forall i = 1,2,3,...$ where $K_i$ are constants. I have a problem in writing the Lagrange's ...
2
votes
1answer
205 views
significance of maxima and minima of time varying kinetic energy of a system
Consider a system of particles where the kinetic energy of the system is varying with time. I'd like to know the significance (or meaning) of the time derivative of the kinetic energy being zero at a ...
5
votes
1answer
109 views
Sum of angular momentum of all electrons in a magnet
Can the sum of angular momentum of all rotating electrons in all the aligned atoms in a permanent magnet have a significant contribution to the macro angular momentum of the magnet? If yes, why does ...
0
votes
2answers
125 views
In a 2D problem with a thrown object, why is the acceleration along the x-axis equal to 0?
I'm starting Physics, and I don't understand why the acceleration along the x-axis is zero for an object thrown near the surface of the Earth. This may be problem specific, but I wouldn't know since I ...
7
votes
2answers
603 views
Forget Hooke's law. Why does a spring exert a force?
Forgetting Hooke's law for a minute why, from a microscopic perspective (preferably quantum) on up to a macroscopic one, does a spring under tension exert a force?
I was thinking that there might be ...
3
votes
3answers
323 views
Why trimming the mainsail gives a larger torque to head up
I am learning sailing on a 5m catamaran (Nacra 5).
I am familiar with basic aerodynamics and the physics of the sail and keel.
We learned that when sailing closed hauled, too tight a mainsail tends ...
-1
votes
1answer
193 views
purely hypothetically, could a quantum being appear to be human? I ask for the purpose of research on a novel [closed]
I am a budding novelist, and im researching a few things for a fictional narrative. the characters are from other dimensions and i want to present a coherent scientific structure. any suggestions ...
4
votes
3answers
319 views
How fast do I need to go in order to avoid being seen by the Police?
I was driving down the road at roughly the speed of traffic. I saw a police officer parked on the side of the road, and also noticed that a Semi was traveling in the lane right next to him. This got ...
0
votes
1answer
387 views
Distance traveled by a projectile into a block
This problem is part of one of the free response questions on the 2011 AP Physics C Mechanics exam [PDF of free-response questions] that was administered last week.
(Sorry the problem statement is so ...
0
votes
2answers
2k views
Homework Help - Physics / Calculus III / Force-Work Problem
I have tried to answer the problem correctly, and I have found similar (and even an identical) problem in my textbook, yet I still can't seem to yield the correct answer with this specific problem.
...
2
votes
2answers
977 views
Distribution of forces
(little background: I'm trying to develop a small, quick 'n dirty static physics engine to determine whether a stacking of boxes is stable).
If I have a 3D rigid box (with the bottom in the ...
3
votes
2answers
670 views
Formula for implementing a simulated weighing scale
Background:
I'm on the pledge drive committee for a non-profit group, and there is an issue that is always contentious within this group; thankfully the group is amicable, although competitive, about ...
0
votes
3answers
3k views
Period of Precession
I'm trying to find the period of precession for a gyroscope. Now I was able to find the angular precession rate, which was 1.132 rad/s, but I have no idea how to convert this to a 'period', and google ...
0
votes
0answers
187 views
Does angry birds have randomness or just chaos [closed]
Does angry birds have randomness or just chaos?
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 ...
-1
votes
3answers
471 views
what energies do the wheels of a moving car posses?
I saw this question in a test. I would have answered kinectic energy due to rotation and translation. It that correct. Else what is the answer?
Oh no, i forgot to mention it was objective type ...
3
votes
1answer
496 views
How do anti-lock brakes know when to brake?
When you come to a stop normally, the brakes don't pulse when you stop. Since the car can only know its speed by the rotation of the wheels, how can it distinguish between the car is stopped normally ...
0
votes
3answers
674 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 ...
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 ...
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 ...
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 ...
1
vote
3answers
507 views
Most elegant/fundamental formulations of the laws of classical mechanics?
Newton tried to do it with three laws/statements. While the first can be derived from the second, the three form a pretty nice framework.
Later on, I've encountered Lagrangian Mechanics, which ...
0
votes
2answers
316 views
Terminal velocity for falling in a shaft
One falls slower in a mine shaft than in free air. This is due to collisions with the walls. How should one model the terminal velocity in the presence of such collisions?
0
votes
3answers
551 views
Impulse - distance question
What impulse should be applied to an object of mass m, having a known coefficient of friction u to get to a distance d ?
Thanks!
Update 14.02.2011:
I still wasn't able to find an answer to this. ...
20
votes
4answers
2k views
Why is the bell, well, bell shaped?
What is the significance about the bell shape, when its hit at the rim it rings/produces sound better than other shaped objects? If so could anyone explain a little bit on it.
EDIT: From the ...
1
vote
1answer
444 views
How to determine velocity and mass of asteroid 2011 CQ1
As you may have seen, a small asteroid had a near miss with the earth a few days ago.
As a physics teacher teaching momentum, I think this could be an excellent problem for my students, however, I ...
8
votes
2answers
360 views
Shaking a jar of balls
A jar is filled with two types of balls, red and green. Red balls have radius $r_1$ and mass $m_1$, green balls have radius $r_2$ and mass $m_2$.
If initially the balls are randomly placed throughout ...
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):
...
-2
votes
2answers
165 views
Non Classical mechanic answer to : length of time a thrown object spends in rest before falling down? [closed]
When an object is thrown upwards, when it eventually comes to rest and starts falling, for how long is it stationary? What about an particle in electric field having an initial velocity towards it's ...
12
votes
9answers
906 views
What are good mechanics experiments for 10 year olds?
I'm trying to explain elementary mechanics - without the benefits of calculus or even algebra - and struggling. I'd like to find reasonable ways to demonstrate Newton's laws, minimally, and possibly ...
