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.
2
votes
0answers
76 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
287 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
293 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
533 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
476 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 ...
3
votes
4answers
938 views
“Regular” 20-sided die, vs “life counter” 20-sided die. Same probabilities?
Regular dice are made such that opposite sides of the die add to 1+the number of sides.
For example, a 20-sided die has 14 and 7 opposite of each other, adding to 21.
For certain types of games, ...
6
votes
2answers
391 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 ...
5
votes
2answers
170 views
Tracking photon color in Bell experiments
In parametric down-conversion, it is said that a driving photon is converted into two entangled photons whose frequencies add up to the driving frequency. Yet in discussions about entanglement ...
3
votes
1answer
185 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 ...
0
votes
0answers
230 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
174 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 ...
1
vote
3answers
1k views
A spinning bullet
I know the rifling in a gun or rifle puts a spin on the bullet along the axis of trajectory. Now I don’t understand exactly what does it make the trajectory more stable and the travel grater?
2
votes
2answers
542 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
2answers
370 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 ...
1
vote
2answers
426 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)? ...
2
votes
0answers
143 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
...
1
vote
2answers
289 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
2answers
269 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 ...
5
votes
1answer
110 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 ...
2
votes
1answer
217 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 ...
0
votes
2answers
131 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
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?
2
votes
2answers
131 views
Mechanical work to required battery power
I have a very practical question where I've calculated the mechanical work needed by a simple mechanical system by solving the line integral $W = \int_C \ F \ dx$. However, since I have a black spot ...
7
votes
2answers
607 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 ...
-1
votes
1answer
204 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
320 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 ...
2
votes
1answer
518 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
3answers
333 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 ...
0
votes
1answer
389 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 ...
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?
3
votes
2answers
700 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 ...
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. ...
14
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 ...
0
votes
0answers
189 views
Does angry birds have randomness or just chaos [closed]
Does angry birds have randomness or just chaos?
5
votes
1answer
155 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 ...
2
votes
2answers
1k 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 ...
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 ...
3
votes
1answer
522 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 ...
-1
votes
3answers
483 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 ...
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
521 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 ...
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
3answers
314 views
How does solar activity affect the ISS?
Currently the sun is launching some intense solar flares.
http://www.guardian.co.uk/science/2011/feb/17/solar-flares-northern-lights-uk
Th article I've linked also mentions how a "coronal mass ...
0
votes
3answers
565 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. ...
1
vote
1answer
451 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
364 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 ...
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.
...
0
votes
2answers
600 views
Mechanical energy problem
Question goes: "An anvil hanging vertically from a long rope in a barn is pulled to the side and raised like a pendulum 1.6 m above its equilibrium position. It then swings to its lowermost point ...
1
vote
4answers
332 views
Will tensile strength keep a cable from snapping indefinitely?
Trying to secure a wall hanging using magnets; me and a coworker came up with an interesting question:
When the hanging is hung using 1 magnet, the weight of it causes it to quickly drag the ...
-2
votes
2answers
167 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 ...
