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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5
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1answer
729 views

wind vs air resistance

I'm wondering which offers more resistance: pulling an object at some speed through air, or holding the object steady against wind at the same speed. I think initially people would think same ...
-1
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1answer
2k views

Can I just ask what these pulleys-and-constant-lengths problems are called?

I am not sure if this question is appropriate for this section, but I just want to know what these type of questions are called and when do physics majors learn them? These problems have to do with ...
7
votes
2answers
5k views

How can an an ant lift 50 times its own weight and pull 30 times its weight?

According to many sites like this one, an ant can apparently lift 50 times its own weight and pull 30 times its weight. Is it true? Can it be proved using physics? Though most sites agree that an ...
0
votes
1answer
704 views

Can anyone solve this simple static equilibrium problem? [closed]

A bridge is 50m long, has a mass of 20,000kg, and rests on two pivots, A and B. The distance between A and the left side of the bridge is 10m. The distance between B and the right side of the bridge ...
1
vote
2answers
1k views

When should we use the concept of Impulse/Momentum instead of Force?

In my notes it says "The ideas of impulse and momentum is useful in solving problems where:- a) the force F is not easily calculable (e.g. sudden impact or blow) b) the impulse force is ...
6
votes
1answer
1k 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, ...
3
votes
0answers
2k 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 ...
1
vote
2answers
788 views

Ropes and Pulleys - Really unintuitive answer

I usually don't want to do this, but please go to this link, the solution is too big to post it here http://engineering.union.edu/~curreyj/MER-201_files/Exam2_2_26_09_Solution.pdf And go to page 5 ...
2
votes
5answers
521 views

Find drag force on link of rotating chain

Given a closed chain with a total length of 1.2m rotating at 1'800 rpm and a total mass of 0.4kg, what is the drag force pulling on one chain link? I originally thought that since no link size was ...
5
votes
3answers
1k views

Why are there 4 Dimensions and 4 Fundamental Forces?

Is it a coincidence that there are four fundamental forces and four spacetime dimensions ? Does a universe with three spacetime dimension contain four fundamental forces? Can magnetism be realized in ...
1
vote
2answers
1k views

Infinite Atwood's machine

I tried doing the following problem just for fun (please see the following link): (I'm not allowed to post the entire problem here since I'm a new user.) Here are my equations: ...
-1
votes
1answer
612 views

Ping pong ball levitation control system question, modeling as a damper? [closed]

I am building a control system to levitate a ping pong ball at a given height in a clear plastic tube using an arduino and implementing PID control. I have to come up with a transfer function... I am ...
0
votes
0answers
85 views

Springs yet again, this time with a picture. Infinite displacement, makes no sense [duplicate]

Possible Duplicate: How could this damped oscillator ever go to infinity? Or negative infinity for that matter? Consider this ! Where I purposely drew the right arrow bigger than the left ...
5
votes
1answer
479 views

Lorentz force law in Newtonian relativity

I know that in special relativity Electric and Magnetic fields mix together in different reference frames, but my question is about classical mechanics. It seems weird to me is that the Lorentz Force ...
0
votes
1answer
279 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 | ...
0
votes
2answers
3k views

Two objects exert forces on each other, will the reactions affect them?

Two objects go in against each other, and then they collide, will object 1, exerting force 1, necessarily get on it a reaction equal in magnitude and opposite in direction? EDIT:- In my book it only ...
1
vote
1answer
3k views

Can we determine the force an object exerts by its mass and acceleration?

I understand that the objects acceleration is determined by the force exerted on it, and that the force exerted on it is determined by its acceleration. But, does an object's (named A) acceleration ...
8
votes
3answers
442 views

Whether $m$ in $E=mc^{2}$ and $F=ma$ are both relativistic mass?

I know that $m$ in $E=mc^{2}$ is the relativistic mass, but can $m$ in $F=ma$ can also be relativistic? If the answer is yes, then can you tell me whether this equation is valid $E=\frac{F}{a}c^{2}$? ...
0
votes
3answers
746 views

Question involving Vectors and Forces

This is a question I found in Mechanics for Engineers by Beer & Johnston. A 600-lb crate is supported by the rope and pulley arrangement as shown below. Write a computer program which can be ...
4
votes
4answers
1k views

Example in the book: A simple accelerometer

A simple accelerometer You tape one end of a piece of string to the ceiling light of your car and hang a key with mass m to the other end (Figure 5.7). A protractor taped to the light allows you ...
2
votes
2answers
273 views

Raising a toolbox with a rope

Suppose you use a rope to hoist a box of tools vertically at constant speed v. The rope exerts a constant upward force of magnitude F_up on the box, and gravity exerts a constant downward force (the ...
-1
votes
1answer
703 views

How should I draw this free-body diagram?

The horizontal force P acts on the rim of the homogeneous cylinder of radius R and weight W. Determine the smallest coefficient of static friction that enables the cylinder to start rolling up the ...
-1
votes
1answer
264 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
671 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
vote
1answer
422 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
121 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
vote
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
344 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
825 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
vote
1answer
433 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
513 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
vote
1answer
916 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
624 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
168 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
558 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
241 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
320 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
504 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
299 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
229 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 ...