# Tagged Questions

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.

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### 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 ...
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 ...
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 ...
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 ...
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 ...
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### 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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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?
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### 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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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### 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 ...
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 ...
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 ...
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. ...
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### 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 ...
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 ...
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 ...
187 views

### Does angry birds have randomness or just chaos [closed]

Does angry birds have randomness or just chaos?
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### 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 ...
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### 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 ...
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 ...
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 ...
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### 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 ...
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 ...
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 ...
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### 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 ...
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?
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. ...
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 ...
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### 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 ...
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 ...
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): ...