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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-1
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1answer
266 views

Find largest angle

The two homogeneous bars AB and BC are connected with a pin at B and placed between rough vertical walls. If the coefficient of static friction between each bar and the wall is 0.4, determine the ...
2
votes
1answer
676 views

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 ...
1
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1answer
426 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 ...
2
votes
1answer
163 views

Could someone explain to me why this is sometimes right and sometimes not?

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 ...
5
votes
2answers
122 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 ...
1
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2answers
5k 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 ...
1
vote
1answer
345 views

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 ...
6
votes
4answers
838 views

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.
1
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1answer
440 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 ...
0
votes
1answer
523 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 ...
1
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1answer
932 views

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 ...
5
votes
1answer
628 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 ...
0
votes
1answer
2k 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 ...
2
votes
2answers
1k 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: ...
3
votes
2answers
2k views

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 ...
2
votes
1answer
169 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 $m_1$ ...
10
votes
4answers
3k views

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

The electromagnetic force on a charge $e$ is $$F=e(E+v\times B),$$ the Lorentz force. But, is this a separate assumption added to the full Maxwell's equations? (the result of some empirical ...
-2
votes
1answer
115 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 ...
3
votes
3answers
563 views

About constructing potential energy functions

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 ...
3
votes
2answers
242 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 ...
1
vote
2answers
103 views

Nonabelian gauge theories and range of the corresponding force

Do all nonabelian gauge theories produce short range force?
3
votes
1answer
324 views

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 ...
3
votes
2answers
506 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 ...
6
votes
1answer
4k views

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 ...
0
votes
3answers
273 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 ...
0
votes
2answers
4k views

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 ...
3
votes
2answers
301 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 ...
2
votes
1answer
232 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 ...
3
votes
1answer
244 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 $\frac{E}{\epsilon}$, ...
7
votes
4answers
480 views

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 ...
4
votes
2answers
339 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?
0
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3answers
3k views

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. ...
1
vote
2answers
270 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 ...
1
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1answer
2k views

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 ! ! Quick Concept Check a) Could someone briefly explain to me ...
5
votes
4answers
1k 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 ...
2
votes
3answers
2k views

Why did they add a Centripetal Force in the Free-Body Diagram?

problem ! solution ! Why do they have the centripetal force in there? I understand that the normal force is the centripetal force here, but why would they say "or $\frac{mv^2}{r}$"? I thought it ...
2
votes
2answers
509 views

Why did they omit the action-reaction pair force in this problem?

Problem ! Solution ! My solution ! Let me explain $n_{bg}$ means the force exerted by the block on the ground. This is because the normal force of the slab exerts (or touches) a force on the ...
2
votes
2answers
1k views

This is going to sound really stupid. But how do I change my normal force?

Suppose I am going to the doctor's and I want to do either of the following Make myself lighter on the scale Make myself heavier on the scale For 2), isn't it just relaxing and let your mass drop? ...
0
votes
3answers
1k views

Who is right? Force exerted on a body. Me or my friend?

Three masses $m_1 = 3\text{ kg}$, $m_2 = 9\text{ kg}$ and $m_3 = 6\text{ kg}$ hang from three identical springs in a motionless elevator. The elevator is moving downward with a velocity of $v = ...
5
votes
8answers
1k views

Physics Paradox about Newtons Second Law $F=ma$

If force equals mass times acceleration, wouldn't a basketball dropped from the top of the Eiffel tower exert the same force on the ground as a basketball dropped a foot off the ground? They both ...
3
votes
3answers
7k views

Does a car use friction to move?

When a car's engine injects fuel into the cylinder chambers, the reaction creates a force that generates rotational momentum to the shaft and over the transmission, it translates that power to the ...
1
vote
1answer
601 views

How do I find the force an object exerts on adjacent objects when I push on it?

Suppose that I have a situation like the figure below, with several circular objects in contact. I know: $\vec{A},\vec{B},\vec{C}$: the positions of the points of contact between circles $\vec{O}$: ...
-1
votes
1answer
136 views

Air simulation environment [closed]

I will preface this with the fact that I am not a physicist...I am an engineer by trade. I am working on a research problem that will involve flight of an organism with varying shapes, and I am ...
3
votes
4answers
3k 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 ...
8
votes
0answers
381 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 ...
5
votes
0answers
26 views

Measurement of Tangential Momentum Accomodation? [duplicate]

Possible Duplicate: Measurement of Tangential Momentum Accomodation? I am using atomic force microscopy (AFM) for characterizing pores of the size of nanometers for application in gas ...
0
votes
1answer
184 views

Figuring out the force using Newton's 2nd Law

Here's a problem on my test review: A 12 kg crate resta on a horizontal surface and a boy pulls on it with a force that is 30° below the horizontal. If the coefficient of static friction is ...
1
vote
0answers
831 views

FPS to MKS usage issues

I'm currently taking a high school physics class and we're doing friction problems now. I've been doing the ones that use MKS perfectly well, but when the problems start to use the FPS system, I'm ...
0
votes
1answer
941 views

Solving an indeterminate triangle truss structure (statics)

From the setup of two trusses as shown in this illustration, how can I solve for the axial reaction forces in the trusses, and in the points A and B (Ax, Ay, Bx, By)? It is assumed that the joints ...
7
votes
1answer
271 views

How would nucleosynthesis be different if the neutron were stable?

If the strong nuclear force were just 2% stronger, the neutron would be a stable particle instead of having a half life of about 13 minutes. What difference would that have made to Big Bang ...