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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2answers
132 views
Why aren't stratospheric balloons compressing their helium to descent?
I can't find a reference of a working stratospheric balloon mounted with a compressor to control its altitude. Is there a big physical difficulty (such as compressor weight/power ratio, or power ...
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 ...
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0answers
74 views
How do I figure out the normal force on a person on an accelerating platform? [closed]
My question is an elaboration on this question: Force on rope with accelerating mass on pulley
The elaboration is to determine what the Force that the platform exerts on the person. Assume the ...
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0answers
14 views
What are the applications of Microcontiuum theory, especially mircopolar theory?
I'm reading the book "Microcontiuum Field Theories I: Foundations and Solids". I got some basic idea of microcontiuum theory from the book, but the book provides little illustration on the application ...
0
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1answer
275 views
Stacking gold Bars
I once heard that because gold is so malleable, while also being very heavy; that if one were to stack several layers of bars on top of on another (like is so familiarly depicted in movies & TV), ...
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0answers
25 views
Determine the dilation temperature so as to double the speed
There's a metallic rod of length $l_1$ which is spinning around a vertical ax which passes through its center. The ends of the rod are spinning with $\omega_1$ angular speed. Determine the temperature ...
2
votes
4answers
898 views
Physics behind Wheel Slipping
Lets say that I'm in a car and I apply full acceleration suddenly. Now, the wheels would slip and hence the car doesn't displace much.
But If I start with some constant acceleration, slipping doesn't ...
1
vote
3answers
432 views
Is it possible to find out the distance traveled by a car if the force applied on it is given?
Say you have car which produces $F$ amount of force which is transferred to the wheels directly.
Now assuming that there is air friction which is causing a retarding force proportional to the ...
1
vote
3answers
140 views
What's driving the bucket up?
Just saw this cool video from Plymouth University, which I actually found through Matthen's blog.
They fill a plastic bottle with liquid nitrogen, screw the cap on, drop it in a bucket full of warm ...
1
vote
2answers
70 views
Mechanics Energy (Calculus)
A particle moves with force
$$F(x) = -kx +\frac{kx^3}{A^2}$$
Where k and A are positive constants.
if $KE_o$ at x = 0 is $T_0$ what is the total energy of the system?
$$ \Delta\ KE(x) + \Delta\ ...
0
votes
1answer
106 views
Why is my speed imaginary?
A particle is released from a dense atmosphere free planet of radius r at a distance R (R >> r ). find the speed on impact.
$$F = \frac{GmM}{(r + R)^2} = m \frac{dv}{dt} = mv\frac{dv}{dR}$$
...
14
votes
3answers
603 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 ...
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votes
1answer
176 views
What kind of force is it when you push a door shut? [duplicate]
Possible Duplicate:
How can I stand on the ground? EM or/and Pauli?
It probably seems like a silly question to a physicist, but I'm from a pure maths background and don't know an awful lot ...
0
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0answers
43 views
how do the '3d printed magic arms' work? [closed]
this video has been circulating on the internet in the past couple of months, showing how engineers at the Nemours/Alfred I. duPont Hospital for Children used a 3D printer and the power of elastic ...
4
votes
3answers
390 views
An example of non-Hamiltonian systems
I am preparing for the exam. And I need to know the answer to one question which I can't understand.
"Give an example of non-Hamiltonian systems: in case of infinite number of particles; for a finite ...
0
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1answer
87 views
Horsepower achieved with multiple motors
Scenario
I'm planning to build an electric motor for fun (not for any practical purpose). I recently purchased a shapeoko CNC mill kit and intend to manufacture most of the parts housing, stator etc. ...
3
votes
1answer
125 views
Why is the $\langle v_{x}^{2} \rangle=\frac{1}{3} \langle v^2 \rangle$?
For a randomly moving particle. Or, I suppose that 1/3 could generalise to 1/n, where n is the non rotational degrees of freedom for that particle.
Related reference Kinetic Theory of Gasses.
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6answers
1k views
What will happen if a plane trys to take off whilst on a treadmill?
So this has puzzled me for many a year... I still am no closer to coming to a conclusion, after many arguments that is. I don't think it can, others 100% think it will.
If you have a plane trying to ...
4
votes
1answer
675 views
Rubber Band Forces
I have a question regarding the force a band places on an object. Say I have a rubber band wrapped around 2 pegs at a certain distance, and at that distance I know the pounds of force per inch it is ...
2
votes
4answers
460 views
At same level do these two pipe lines give same pressure of water?
Provided that the two pipe lines are of same length, same material and in the same level, is the water pressure in both the layouts same or different?
PS: In 1st pipeline the turns are not ...
2
votes
4answers
309 views
Which angle causes an object to land quickest?
Say a canon is where the circle is, and it shoots two different canonballs at different angles, but at the same speed, which angle would make the cannonball hit the ground first?
Intuitively I'd ...
0
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0answers
174 views
tension on the hanging chain [closed]
A flexible chain of mass $m$ hangs between two fixed points $a$ and $b$ at the same level. Let the inclination of the chain with horizontal line of the two points of support is $\theta$. What would be ...
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0answers
21 views
How does a treadmill incline mechanism work? [duplicate]
Possible Duplicate:
What's the difference between running up a hill and running up an inclined treadmill?
I want to know how a system can give so many small steps of inclination and so ...
2
votes
2answers
130 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 ...
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 ...
0
votes
2answers
85 views
Can a mechanical systems on hold be switched off, in another way than just letting it do it's thing?
Can the value of the potential energy, which is responsible for driving the system, diminish in time, while the system itself is stationary during that time? Can there be dissipation in a system, ...
4
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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?
0
votes
2answers
741 views
Calculation of the maximum load to the bar
Looking for a way of calculating the maximum weight (W) to the rod with the given length (L) where the rod did not break and that only bend for (b) mm.
Need only approximative solution (read: ...
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 ...
2
votes
4answers
330 views
pendulum on a rotating table. Will a torque be generated?
Here is the set up. Very simple. A flat (i.e. horiozntal table, there is no gravity) and rounded table that spins on its axis (through the center of the table). A spring mass system is now put on the ...
2
votes
1answer
162 views
Static plane in an inertial frame of reference
Suppose we are given a mechanical frame consisting of two points. How can we prove that assuming any initial conditions there is an inertial frame of reference in which these points will be in a ...
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
1answer
169 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 ...
2
votes
2answers
125 views
Is it possible to control a treadmill's tread speed such that a plane on the treadmill will be prevented from moving?
I've posed the question in this particular way to avoid the ambiguity usually found in the posing of the "airplane on a treadmill" puzzle, e.g.
I'm not specifying how the treadmill is controlled but ...
5
votes
2answers
169 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 ...
0
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0answers
115 views
Mechanics of solid problem [closed]
A thick-walled cylinder is made of multiple layers of differing homogenous isotropic elastic solids and are assembled without any interference. If the internal and outer radii of each layer is known, ...
2
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2answers
269 views
What is the purpose of iron bars in concrete?
What purpose do iron rods in concrete serve?
Do these iron rods impart any strength to the concrete apart from defining the framework for the concrete to solidify upon initially?
2
votes
4answers
118 views
Path traced out by a point
While studying uniform circular motion at school, one of my friends asked a question:
"How do I prove that the path traced out by a particle such that an applied force of constant magnitude acts on ...
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 ...
3
votes
3answers
353 views
What makes the earth keep spinning?
I am thinking of what makes the earth keep spinning. Is there anybody here know the answer?
1
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1answer
193 views
Euler's buckling formula applicable for impact calculations?
$$F = \frac{\pi^2 EI}{(KL)^2}$$
Is Euler's buckling formula applicable for impact calculations, considering speeds relevant for a car or aircraft crash?
If there is a level where the formula ...
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 ...
3
votes
1answer
506 views
What phrases describe collisions with coefficients of restitution less than zero or greater than one?
The coefficient of restitution describes the elasticity of a collision:
1 = perfectly elastic, kinetic energy is conserved
0 = perfectly inelastic, the objects move at the same speed post impact
...
0
votes
3answers
197 views
How to determine an exponential acceleration curve?
I've always been not so bad in mathematics, but I'm terribly bad at physics. For me, abstract concept are totally understandable, but when it come to reality, I'm lost !
So, for my job, I need to ...
2
votes
1answer
137 views
Will a precessing spinning whell fall down if there is no friction at all?
If there where no friction at all, would a spinning wheel held up by one end of the axis spin precess forever without falling down?
I just asked another question about the same problem:
Direction ...
12
votes
4answers
874 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 ...
0
votes
0answers
215 views
How to decide velocity profile for two stepper motor in robot driving
A robot has 2 parallel driving wheel. I don't know the friction of the ground surface. However, I can set the acceleration, starting velocity, ending velocity. The velocity profile has to be ...
2
votes
3answers
138 views
Effect of surface treatment on fair dice
If I have a perfectly balanced and thus fair cubic die, then polish 3 adjacent faces (so that their coefficient of friction is effectively zero) and roughen the remaining faces (so that their ...
2
votes
2answers
203 views
What sustains a rigid body's rotation at its constant angular(rotational) speed?
Continuing from the following scenario from my previous question Centripetal force of a rotating rigid body? :
Consider someone pushing a roundabout in a playground. Initially the
roundabout is ...
2
votes
2answers
301 views
What happens when the string slackens during vertical circular motion?
Consider a particle attached to one end of a string of length $l$ moving anti-clockwise in a vertical circle whose centre is $O$. What exactly happens physically when the string becomes slack and ...
