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.
27
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 ...
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 ...
16
votes
4answers
1k views
How does a car turn without any skidding?
The rear wheels of a car always face in the direction the car is moving. The front wheels are able to turn left or right and thus can point in the direction the car is moving towards. What I don't ...
14
votes
3answers
614 views
Why doesn't a fly fall off the wall?
Pretty simple question, but not an obvious answer at least not to me. I mean you can't just place a dead fly on the wall and expect it to stay there, he will fall off due to gravity. At first I ...
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 ...
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 :-)
12
votes
9answers
938 views
What are good mechanics experiments for 10 year olds? [closed]
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 ...
12
votes
4answers
895 views
How to sail downwind faster than the wind?
Recently a group set a record for sailing a wind-powered land vehicle directly down wind, and a speed faster than wind speed. Wikipedia has a page talking about it, but it doesn't explain exactly how ...
11
votes
4answers
1k views
How can I measure the mass of the earth at home?
How can I measure the mass of the earth at home?
How was the mass of the earth first measured?
11
votes
2answers
460 views
A problem inspired by the ice hockey game
Question shortly:
How far would a hockey puck slide in two different cases:
The puck is sliding (translation) on ice and spinning on its flat surface.
The puck is sliding on ice without spinning. ...
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 ...
9
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 ...
9
votes
5answers
323 views
Driving on snowy roads
'tis the season as they say!
It seems to me obvious that it's better to drive in high gear on snowy roads to reduce the torque.
However, there are completely opposite advices being given on ...
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 ...
8
votes
2answers
229 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 ...
8
votes
1answer
96 views
Are Carnot engine efficieny and Fourier heat trasmission law related?
It just occured to me that the efficiency of Carnot cycles is $\eta= \frac{T_1 - T_2}{T_1}$, that is, the efficiency decreases as the difference between reservoir temperatures decreases. On the other ...
8
votes
3answers
180 views
Is $k_B \rightarrow 0$ the classical limit of stat. mech., as $\hbar \rightarrow 0$ is in QM?
I hear very often among my peers and seniors that just as how $\hbar\rightarrow0$ takes me to classical mechanics from quantum mechanics, $k_B\rightarrow0$ will take me to classical thermodynamics ...
8
votes
4answers
507 views
Shape of rotating rope (lasso problem?)
Let's take a wire or a rope. I usually do this with a chain or my scarf.
I fixate one end in my hand and apply rotation (by subtle movements of this endpoint like spinning a lasso). The rope gets ...
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 ...
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?
7
votes
2answers
516 views
How fast does force propagate through matter? [duplicate]
Possible Duplicate:
Is it possible for information to be transmitted faster than light?
Consider the following thought experiment. You have a long perfectly rigid beam (for the sake of ...
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 ...
7
votes
1answer
508 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. ...
7
votes
1answer
91 views
Is there a trajectory which is not a solution of the equation of motion but satisfies all conservation laws?
I'm wondering whether conservation laws are sufficient to imply equations of motions. Specifically:
1) In classical mechanics of point particles, are conservation of energy, conservation of momentum ...
7
votes
1answer
174 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
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 ...
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. ...
6
votes
2answers
169 views
Which is more efficient: a larger wheel or a smaller wheel?
I'm designing a 2-wheeled cart that I plan to rig to a donkey for hauling work around a farm. I'm wondering if there are mechanical advantages to using smaller wheels (like 40 cm diameter) vs. using ...
6
votes
2answers
259 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 ...
6
votes
1answer
163 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 ...
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
4answers
6k views
Is pushing actually easier than pulling?
It is generally assumed that pushing a cart is more easier than pulling one. But why?
Is there any difference in terms of force required to achieve the same amount of displacement?
Or is it just a ...
5
votes
2answers
561 views
What determines the (minimum) angle at which a domino falls over?
Dominoes, when placed upright, remain that way. Sometimes, even if you tip them a little bit, they will go back to their upright position.
However, if you tip them too far, they will fall over.
...
5
votes
5answers
790 views
The Z-Torque: how can it be shown intuitively that it does not work?
There is a new kickstarter project that claims to increase torque and power compared to a normal crank on a bicycle (Z-Torque on kickstarter). If this patented (US Patent Number 5899119) approach ...
5
votes
2answers
340 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 ...
5
votes
1answer
470 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 ...
5
votes
2answers
136 views
Conceptually, what is negative work?
I'm having some trouble understanding the concept of negative work. For example, my book says that if I lower a box to the ground, the box does positive work on my hands and my hands do negative work ...
5
votes
2answers
544 views
Ball Rolling in a Parabolic Bowl
I encountered a physics problem which inquired about a ball rolling inside a parabolic bowl (i.e. a bowl where any cross section through the vertex would make a parabolic shape given by $y = kx^2$). ...
5
votes
1answer
214 views
Drag on a spinning ball in fluid
I am a physics newbie (high school level) and I am wondering what happens when a spherical object is spinning on the spot in a bunch of gas (no gravity here, just an imaginary physics sandbox).
Am I ...
5
votes
1answer
173 views
Does a straight water hose issue water at a greater pressure than a Coiled water hose of same diameter and length?
I have a one BHP water pump, the water pressure of a coiled hose connected to the water pump output side was not that great. Would an unwound water hose produce greater water pressure? [Friction ...
5
votes
1answer
65 views
Calculating how a polygon bounces off a plane
I'd like to calculate how polygons bounce off a plane. In this picture, the square doesn't bounce straight up, but instead it bounces somewhat to the right and starts spinning. But I have no idea ...
5
votes
2answers
254 views
Row of pivoted magnets and energy scale
This question is about a system involving a horizontal row of length L of equally spaced pivotable magnets, each with a pole at either end. These magnets will often be referred to as units.
So each ...
5
votes
2answers
145 views
Why does motion help you balance on ice skates?
It's almost impossible to balance on a single ice skate if you're standing still. But give yourself just a little forward motion—it doesn't take very much—and it suddenly becomes easy. You can stand ...
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 ...
5
votes
3answers
902 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? ...
5
votes
2answers
272 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
3answers
482 views
List of Scattering Phenomena
While at lunch with my lab group we got into discussion of the different types of scattering phenomenon that we encounter in everyday life and physical experiments. We ended up listing about a dozen ...
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 ...
5
votes
1answer
54 views
Fresco in his “Future By Design” introduces drawing of underwater vessel and its front system of generating air bubbles. Is idea energy efficient?
I recently saw Fresco's Future By Design and noticed something miniature to investigate.
My notice regards about one of his illustration he describes in the documentary. Here is the link on youtube, ...
