This tag is for the classical concept of forces, i.e. the quantities causing an acceleration of a body. It expands to the strong/electroweak force only insofar as they act comparable to ‘classical’ forces. Use [tag:particle-physics] for decay channels due to forces and [tag:newtonian-mechanics] or ...
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The Time That 2 Masses Will Collide Due To Newtonian Gravity
My friend and I have been wracking our heads with this one for the past 3 hours...
We have 2 point masses, $m$ and $M$ in a perfect world separated by radius r. Starting from rest, they both begin to ...
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7answers
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What does it mean to say “Gravity is the weakest of the forces”?
I can understand that on small scales (within an atom/molecule), the other forces are much stronger, but on larger scales, it seems that gravity is a far stronger force; e.g. planets are held to the ...
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5answers
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Is there an equation for the strong nuclear force?
The equation describing the force due to gravity is $$F = G \frac{m_1 m_2}{r^2}.$$ Similarly the force due to the electrostatic force is $$F = k \frac{q_1 q_2}{r^2}.$$
Is there a similar equation ...
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8answers
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How exactly does curved space-time describe the force of gravity?
I understand that people explain (in layman's terms at least) that the presence of mass "warps" space-time geometry, and this causes gravity. I have also of course heard the analogy of a blanket or ...
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2answers
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Balloons and lifting gases
Hydrogen is the lightest element, so it's cable of lifting the most weight in out atmosphere (probably not the best terminology there, but you get the picture)
Would hot hydrogen (in the same sense ...
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2answers
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Tension in a curved charged wire (electrostatic force) - does wire thickness matter?
Consider a conducting wire bent in a circle (alternatively, a perfectly smooth metal ring) with a positive (or negative) electric charge on it. Technically, this shape constitutes a torus. Assume ...
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9answers
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What's the core difference between the electric and magnetic forces?
I require only a simple answer. One sentence is enough... (It's for high school physics)
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2answers
604 views
Why I think tension should be twice the force in a tug of war
I'm going to provide my argument for why I think the tension in a rope should be twice the force exerted on either side of it.
First, let's consider a different example.
Say, there is a person named ...
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4answers
800 views
Helicopter in an Elevator
You buy one of those remote control toy helicopters. You bring it into an elevator. The elevator goes up. Does the helicopter hit the floor or does the floor of the elevator push the air up into the ...
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4answers
604 views
Alternate layman's metaphors for illustrating curved space-time
The metaphor of a surface (typically a pool table or a trampoline) distorted by a massive object is commonly used as a metaphor for illustrating gravitationally induced space-time curvature. But as ...
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3answers
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Is gecko-like friction Coulombic? What is the highest known Coulombic $\mu_s$ for any combination of surfaces?
Materials with large coefficients of static friction would be cool and useful. Rubber on rough surfaces typically has $\mu_s\sim1-2$. When people talk about examples with very high friction, often ...
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2answers
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Why isn't Higgs coupling considered a fifth fundamental force?
When I first learned about the four fundamental forces of nature, I assumed that they were just the only four kind of interactions there were. But after learning a little field theory, there are many ...
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4answers
798 views
How far does a trampoline vertically deform based on the mass of the object?
If a baseball is dropped on a trampoline, the point under the object will move a certain distance downward before starting to travel upward again. If a bowling ball is dropped, it will deform further ...
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1answer
83 views
How soon that a force affect another object?
Imagine this scenario: I have 2 objects in vacuum without any force exerted upon them not even a possible gravitational force between them.
Now if one of them gets a gravitational or magnetic force, ...
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votes
5answers
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Newton's second law of motion in terms of momentum
I am reading a document and in answer to the question State Newton’s second law of motion the candidate answers that The force acting on an object equals the rate of change of momentum of the object. ...
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1answer
304 views
A Question about Virtual Work related to Newton's Third Law
In describing D'Alembert's principle, the lecture note I was provided with states that the total force $\mathbb F_l$ acting on a particle can be taken as,
$$\mathbb F_l=F_l+\sum_mf_{ml}+C_l,$$
...
3
votes
2answers
492 views
Classical car collision
I have a very confusing discussion with a friend of mine.
2 cars ($car_a$ and $car_b$) of the same mass $m$ are on a collision course. Both cars travel at $50_\frac{km}{h}$ towards each other.
They ...
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2answers
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Did the researchers at Fermilab find a fifth force?
Please consider the publication
Invariant Mass Distribution of Jet Pairs Produced in Association with a W boson in $p\bar{p}$ Collisions at $\sqrt{s} = 1.96$ TeV
by the CDF-Collaboration, ...
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0answers
284 views
Measurement of Tangential Momentum Accomodation?
(this question is a crosspost from theoretical physics.)
I am using atomic force microscopy (AFM) for characterizing
pores of the size of nanometers for application in gas flow. For
this, knowing ...
3
votes
2answers
154 views
Does constraint for speed of Electric and magnetic fields violates Conservation of momentum or Newton's third law?
I'm just a beginner so bear with me. Consider two frames at rest wrt to each other separated by distance enough for light to take a minute or so. At a given instant we create two large dipoles by some ...
3
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2answers
218 views
The Double Integrator: Matching velocity and position as quickly as possible with only a limited amount of force available
If a body with mass $m$ begins at position $x_0$ with velocity $v_0$ and experiences a force that varies as a function of time $f(t)$ (and we ignore gravity, friction, and everything else that might ...
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2answers
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Strongest force in nature
Possible Duplicate:
What does it mean to say “Gravity is the weakest of the forces”?
It is said nuclear force is the strongest force in nature..
But it is not true near a black ...
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1answer
83 views
Explanation of a Foucault pendulum
The equations of motion of a Foucault pendulum is given by:
$$\ddot{x} = 2\omega \sin\lambda \dot{y} - \frac{g}{L}x$$
$$\ddot{y} = -2\omega \sin\lambda \dot{x} - \frac{g}{L}y$$
where $\omega$ is ...
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2answers
378 views
Homework about spinning top
I have a top of unknown mass that has a moment of inertia $I=4\times 10^{-7} kg \cdot m^2$. A string is wrapped around the top and pulls it so that its tension is kept at 5.57 N for a distance of .8 ...
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2answers
525 views
Flying a toy helicopter inside an accelerating train
Scenario:
You ride in a train, you have this helicopter toy. The train is not yet running when you flew your helicopter on a constant altitude (say 1 meter above the train's floor).
Question:
What ...
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1answer
240 views
Mass points of a Mass-spring model
Let's say I have a mass spring model like the one in the picture below:
So, there are 3 parts of the spring joined together in an equilateral triangular manner. Each of the joints has a mass of ...
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votes
2answers
233 views
Force applied off center on an object
Assume there is a rigid body in deep space with mass $m$ and moment of inertia $I$. A force that varies with time, $F(t)$, is applied to the body off-center at a distance $r$ from its center of mass. ...
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1answer
327 views
Calculating torque in a structure
I posted this on math stack exchange but realize it is more a physics question.
I have a structure which is set up as shown in the image. A weight hangs from point A with mass $m$. Joint B is free ...
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1answer
114 views
Question about interaction between three objects
I have been thinking of Newton (insert bad words because of frustration) laws for hours and hours today, and I'm not going anywhere. I'm going insane! So, I made up this question.
Object A | ...
46
votes
7answers
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Does juggling balls reduce the total weight of the juggler and balls?
A friend offered me a brain teaser to which the solution involves a $195$ pound man juggling two $3$-pound balls to traverse a bridge having a maximum capacity of only $200$ pounds. He explained that ...
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3answers
417 views
How does $F = \frac{ \Delta (mv)}{ \Delta t}$ equal $( m \frac { \Delta v}{ \Delta t} ) + ( v \frac { \Delta m}{ \Delta t} )$?
That's how it's framed in my Physics school-book.
The question (or rather, the explanation) is that of the thrust of rockets and how the impulse is equal (with opposite signs) on the thrust-gases and ...
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5answers
3k views
How does centrifugal force work?
I know what centrifugal force is, but how does it work? Why are things forced to the outside?
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2answers
607 views
When does not Newton's 3rd law apply?
Is Newton's 3rd law valid in non-inertial frames?
If so, then are there other cases for which Newton's 3rd law is not applicable?
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3answers
549 views
Is the normal force a conservative force?
Most of the time the normal force doesn't do any work because it's perpendicular to the direction of motion but if it does do work, would it be conservative or non-conservative?
For example, consider ...
6
votes
2answers
586 views
Can a force in an explicitly time dependent classical system be conservative?
If I consider equations of motion derived from the pinciple of least action for an explicilty time dependend Lagrangian
$$\delta S[L[q(\text{t}),q'(\text{t}),{\bf t}]]=0,$$
under what ...
6
votes
1answer
358 views
Degeneracy Pressure, What is it?
There has been numerous question, some violent even in physics@SE regarding PEP and EM forces.
But what baffles me is what is degeneracy pressure? I know there are 4 fundamental forces- EM, gravity, ...
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votes
3answers
714 views
Define Pressure at A point. Why is it a Scalar?
I have a final exam tomorrow for fluid mechanics and I was just looking over the practice exam questions. They do not provide solutions. But pretty much I have to define pressure at a point and also ...
2
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0answers
542 views
Forces and torques about the CENTER OF MASS of a physical pendulum
I'm currently stumped by the following situation. Say we've got a rectangular physical pendulum (think ruler with a hole-punch at one end).
It's trivial to analyze the motion of the pendulum with the ...
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4answers
531 views
Particles for all forces: how do they know where to go, and what to avoid?
Here's an intuitive problem which I can't get around, can someone please explain it?
Consider a proton P and an electron E moving through the electromagnetic field (or other particles for other ...
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votes
4answers
663 views
How many fundamental forces could there be?
We’re told that ‘all forces are gauge forces’. The process seems to start with the Lagrangian corresponding to a particle-type, then the application of a local gauge symmetry leading to the emergence ...
6
votes
1answer
464 views
Ping-pong ball pontoon
Imagine a vertical pipe (both ends opened) in the water. Drop several ping-pong balls into pipe and cover them with a cylinder. When you have enough balls, the cylinder will float. Now start adding ...
4
votes
3answers
337 views
What keeps particles in an atom from flying away or falling into the nucleus?
In atoms, what force or charge, etc. keeps particles from flying away or into their nucleus? is there a kind of weak-force at work on the atomic scale?
Note I am aware the particle positions are ...
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6answers
424 views
ALL “forces” as manifestations of properties of space-time
I apologize if this seems like a quack question, but I need some insights by those who know much more than me in Physics.
Anyway, the gravitational "force" (not really a force) is a manifestation of ...
4
votes
3answers
1k views
Which will stop first a heavier car or a lighter car?
If the friction from brakes, wind resistance and all such factors remain constat, which will stop first? A heavier car or a lighter car? How will the momentum of the car and graviational pull on a ...
3
votes
1answer
117 views
3 current loops with non-conservation of momentum, when one specifically considers SIGNs
Thought experiment I.
Consider two loops of wire, 2 small dipoles B and C , with a common axis z (facing each other) and (say) 30 cm apart B to C. At the speed of light, information (including a ...
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1answer
354 views
Countersteering a motorcycle
Everyone knows the story about countersteering. For those who don't I will explain it below and after the explanation i will ask my question.
You can watch this short video as a beginning: ...
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1answer
264 views
Force exerted on potential wall
A particle bound in an infinite potential wall at $x=0$ will apply a force on the wall. For a plane wave and imagining it as a fluid bouncing off the reflection wall at $x=0$, find the force in terms ...
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votes
1answer
321 views
How is a magnetic field translated into physical force?
Related to this question
Where do magnets get the energy to repel?
If I have a magnet repelling another, eg one in my hand, the other being pushed along the desk, how do the each of the magnet's ...
5
votes
1answer
119 views
Slinky base does not immediately fall due to gravity
Why does the base of this slinky not fall immediately to gravity. My guess is tension in the springs is a force > mass*gravity but even then it is dumbfounding.
5
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1answer
239 views
What's worse, a full frontal impact or an impact at an offset?
Modern car designs have a crumple zone that absorbs most of the impact in a collision, and a strong "safety cell" in the passenger compartment that protects the passengers. These designs are put to ...
