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.
1
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2answers
282 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
267 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
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 ...
2
votes
1answer
206 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
126 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
604 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
197 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 ...
2
votes
1answer
502 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
326 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
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 ...
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
675 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. ...
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 ...
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 ...
2
votes
2answers
995 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
505 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
475 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
510 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 ...
2
votes
4answers
843 views
Is the Woodward effect real?
Did anyone ever heard about this?I've never seen any serious physicist talk about "mass fluctuations".
Here is the man in his own words http://www.intalek.com/Index/Projects/Research/woodward1.pdf
...
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
310 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
554 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
446 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
361 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
577 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
327 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
166 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 ...
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?
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
1answer
270 views
Lagrangian density of linear elastic solid
I need the general expression for the lagrangian density of a linear elastic solid. I haven't been able to find this anywhere. Thanks.
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 ...
12
votes
5answers
2k views
Why do rockets have multiple stages?
What is the advantage for rockets to have multiple stages?
Wouldn't a single stage with the same amount of fuel weigh less?
Note I would like a quantitative answer, if possible :-)
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 ...
-4
votes
2answers
431 views
Moving from point A to point B in zero-gravity
Here's an proposal on how to get from point A to point B in zero-gravity without using any
propellant and the question why it wouldn't work:
A closed tube, filled with water and a round (solid) ...
7
votes
3answers
1k views
How long it will take for a upright rigid body to fall on a ground
Let's suppose there is a straight rigid bar with height $h$ and center of mass at the middle of height $h/2$. Now if the bar is vertically upright from ground, how long will it take to fall on the ...
4
votes
0answers
788 views
Why does Guillotine have of 45 degreed blade rather than the one parallel to the ground? [closed]
What is the point of having 45 degreed blade in Guillotine? After all, the pressure-Force over Area-blade imposes to the neck is the same either way.
0
votes
1answer
205 views
What happens when I move a very long bar? [duplicate]
Possible Duplicate:
Faster than light information
Hey there,
I just want to make clear that I'm new here and I don't know whether this is the right place to ask such a hypothetical ...
5
votes
3answers
893 views
Equivalent spring-constant for infinite square grid of springs
Consider an infinite square grid, where each side of a square is a spring following Hooke's law, with spring constant $k$.
What is the relation between the force and displacement between two points? ...
3
votes
4answers
555 views
Oscillate a swing without touching the ground
Is is possible to set a swing into oscillations without touching the ground?
This occurred to me while watching the second pirates movie. There is a scene where the ship's crew is suspended in a cage ...
1
vote
1answer
329 views
Cheetah prosthesis efficiency
I want to compare the much-talked about Cheeta running prosthesis to a the normal running process in terms of force and energy, but I don't know where to start. How would you start the comparison? A ...
4
votes
3answers
645 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 ...
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 ...
