Questions tagged [forces]

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 the [particle-physics] tag for decay channels due to forces and [newtonian-mechanics] or one of the other subtopics of [classical-mechanics] for the dynamics of classical systems.

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How are fundamental forces transmitted?

How are the fundamental forces transmitted? In particular I wonder, are all "processes" local, i.e. without superluminal distant interactions? But if they are local, then particles would have to ...
727 views

What conditions must be met for a ball to roll perfectly down an incline without slipping?

What conditions must be met for a ball to roll perfectly down an incline without slipping? A mathematically rigorous definition, please. I honestly don't know where to begin with answering this ...
255 views

Doubt about acceleration of mass on spring

I do not remember when, but a while a ago I was told that for a spring with stiffness $k$ and a mass $m$, the equation $-kx = ma$ never holds. (assume a horizontal spring) So if I was given a problem ...
147 views

What is it called when a fluid will “jump” to grab onto an object that comes very close?

I'm doing an experiment where I bring a probe very close to a well full of fluid and then very slowly lower it to obtain some force deformation values. The material behaves very much like a fluid and ...
21k views

Finding distance when the force is a function of time

I'm having trouble with this homework question A mysterious rocket-propelled object of mass 49.0 kg is initially at rest in the middle of the horizontal, frictionless surface of an ice-covered lake....
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Finding the contact force in a mechanical problem [closed]

what is the proper FBD for this system. I cant decide since the weight is given, but there is tension and contact forces. Things get mixed up. Determine the contact force between the smooth 200-lb ...
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Why can't we ascribe a (possibly velocity dependent) potential to a dissipative force?

Sorry if this is a silly question but I cant get my head around it.
1k views

Wave equation from hooke law - simple question

In the paragraph http://en.wikipedia.org/wiki/Wave_equation#From_Hooke.27s_law it is said, regarding the u(x) function, that Here u(x) measures the distance from the equilibrium of the mass ...
736 views

Laws of Motion: Acceleration to be applied on a free falling object to reduce velocity to 0

Assume that an object of mass 'm' is falling to the earth.The force acting on the same would be F = m*g = 10m (assuming g = 10m/s^2). In this case the velocity of the object at time 't' = 10 seconds ...
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Calculating the force of a mass bearing down on an object

I need to calculate the force of a weight bearing down on a smaller object, constraining it from expansion. The weight bearing down has a much bigger surface area than the smaller object. I know the ...
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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 ...
12k views

Force and Laws of Motion [closed]

While catching a fast moving cricket ball, why do fielders gradually pull back their hands backwards with the moving ball? Please advice which among the following is the correct answer. If both are ...
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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: The ...
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What causes destruction in car crash?

Suppose a car crashes at a speed $v$ against a wall and comes to a stop. Now if the car crashes at $2v$, does that mean it suffers twice as much destruction, if that can be objectively measured? If ...
451 views

Pushing, inertia of a cart system

I have a cart with another cart on top which gets pulled down by another cart on the side. There is no friction. The question is: How strongly do I have to push with $F$ to keep the cart $m_1$ ...
15k views

Can the Lorentz force expression be derived from Maxwell's equations?

The electromagnetic force on a charge $e$ is $$\vec F = e(\vec E + \vec v\times \vec B),$$ the Lorentz force. But, is this a separate assumption added to the full Maxwell's equations? (the ...
129 views

What if the strong force gave up? [closed]

Thinking about the space between the subatomic particles in atom -- and how small they are relative to their atom's size -- isn't it rather convenient that the strength of those forces that govern the ...
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There are many classical systems with different potential functions. My problem is that I do not understand how one can construct a certain potential function for a certain system. Are there any ...
981 views

What would be the optimal weight of a ball if I want to throw it as far as possibile?

Assume the force behind my throw to be X. Assume the point of release is 2 meters above ground. Asume the ball is made of shiny steel. I'm not sure if the material matters, I'm just thinking that ...
119 views

Nonabelian gauge theories and range of the corresponding force

Do all nonabelian gauge theories produce short range force?
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Effects of parallel superconducting plates

Assuming the existence of virtual particle field ( zero point energy field) Casimir force is produced by 2 parallel conducting plates excluding some of the frequencies between the plates, if these 2 ...
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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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How does placing objects in liquids affect the mass?

I was dazing off in my physics class when I came up with this question and I was wondering about it all day. I could not provide myself with an adequate solution, so here I am asking the forum about ...
391 views

Is $f=ma$ an identity?

In his The Principles of Natural Knowledge, Alfred North Whitehead writes that famous $f=ma$ is an identity: It has been popular to define force as the product of mass and acceleration. The ...
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What is the force exerted on a body that doesn't move?

If I push against a brick wall I'm exerting a force against the brick wall the the brick wall will exert the same force against me. These will cancel each other out and neither myself or the wall will ...
745 views

Why doesn't phase space contain acceleration/forces?

I'm watching some Physics lectures on the internet by Leonard Susskind: http://www.youtube.com/watch?v=pyX8kQ-JzHI&feature=BFa&list=PL189C0DCE90CB6D81&lf=plpp_video In this lecture, and ...
686 views

Can non-free forces change the rest mass?

While reading Hobsen et al.'s "General Relativity: An Introduction for Physicists", I came across a bit confusing derivation. Multiplying the 4-force and 4-velocity, the following derivation can be ...
437 views

What force is acting on the charge in the dielectric?

For example I have a dielectric solid with a small charged ball in it. And I have external electric field $E$. So what force is acting on this ball? The field in dielectric is $\frac{E}{\epsilon}$, ...
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How does water carve rock?

How does water carve rock? And more generally, how does a soft material carve a hard material? Obviously it happens, but is it a continual process (every drop of soft water carries away a minute ...
551 views

What frequency photons are involved in mediating physical force?

If the force felt when pushing an object is mediated by the electromagnetic interaction and hence photons, what is their frequency?
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How do I find the tension in additional strings in this problem? [closed]

A mass of 5.00 kg hangs attached to three strings as shown in the figure (see image below). Find the tension in each string. Hint: Consider the equilibrium of the point where the strings join. So ...
330 views

Could someone remind me what this means again? $\nabla U = \pm F$

You know that for a potential function (conservative force/fields) that $\nabla U = \pm \vec{F}$ In math, we don't have that minus sign, we have only the plus one. What does it mean if you get rid ...
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Two problems with free body diagrams. Contradictions (solutions are provided)

This problem is similar, but also different question from my previous question. They are both unfortunately long. Problem/Solution #1 http://img215.imageshack.us/img215/6696/problem2f.jpg! http://...
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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 ...
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Why did they add a Centripetal Force in the Free-Body Diagram?

problem http://img196.imageshack.us/img196/6610/problmus.jpg! solution http://img838.imageshack.us/img838/391/solnd.jpg! Why do they have the centripetal force in there? I understand that the ...
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I think there is something wrong with this problem. How do you know if the vertical acceleration is zero?

Suppose a block with mass $3\ \mathrm{kg}$ is on a frictionless table and a force of $15\ \mathrm N$ pulls it from an angle of $38^\circ$ above the horizontal. 1) What is the apparent weight of ...