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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Pressure or confusion

We all know that pressure is force per unit area. for example we have a pressure of $5N/m^2$, so is the load of $5 N$ acts on the entire area or it acts just at a point i.e. is the load a point load ...
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2answers
103 views

Angular equilibrium on a see-saw

I have a tonne of questions related to see-saw equilibrium because most places I've been to online only deal with horizontal equilibrium - but static equilibrium can occur on an angle too. My ...
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1answer
42 views

Work done by a force

What is the difference between work done by a force and work done against that force? Is it true that work by a force = -(work against that force)?
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1answer
61 views

Work-energy theorem for a system

While studying energy conservation on Morin I found this explanation about the work-energy theorem for a system. The work–energy theorem stated before is relevant to one particle. What if we are ...
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1answer
61 views

Why do a conservative force try to reduce potential energy?

Mathematically I understood the reason why, for a conservative force, $\vec{F}=-\vec{\nabla}U$. Physically this means that a conservative force is always oriented in the direction of greatest ...
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2answers
75 views

Why does force cause acceleration?

Consider a ball placed on a smooth plane. If you take a plank made out of wood and whack it (apply a force on it), does it accelerate because First, the force compresses the part of the ball in ...
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0answers
61 views

Why is the longitudinal term removed to form the Lorentz force equation?

Beginning with the expression for interaction energy, and deriving the potentials form for the force on a test charge moving at velocity $\vec v$ yields: $$\vec F = q(-\nabla\phi - {D\vec A \over ...
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1answer
31 views

The definition of the unit of Force

Below, I quote what my physics textbook says. $$F=kma$$ The units of force are so chosen that this constant of proportionality, $k=1$.Therefore $F=ma$. For this, one unit of force is defined ...
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1answer
40 views

Force and Torque

Think of a uniform sphere. Sometimes if a force is applied to the sphere it does not only move but also spins. So there is a torque. But is it possible to calculate which part of the applied force is ...
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2answers
51 views

Newton's law of gravitational attraction [closed]

My teacher would like us to use Newton's law of gravitational attraction to solve a question similar to this one: "Two objects exert a force of gravity of 20N. One object's mass is increased by a ...
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2answers
516 views

Is Newton second law covariant or invariant?

Is Newton second law covariant or invariant between two inertial frames, moving with uniform traslational motion with respect to each other? If it is invariant then, indipendently from the frame, ...
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0answers
20 views

Kinetic energy vs Kinetic Energy scenario in a collision, mechanical energy used for work?

Most collisions have Kinetic energy conserved or in the case of inelastic collisions energy is lost into other forms. Though the equation of "TMEi + Wnc =TMEf" is true however, what if two unequal ...
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1answer
44 views

What component of the payload appears on the cross member? [closed]

I have a set of DIY steps; I've modelled it as the steps themselves "s", a short vertical support "a", a long vertical support "b" and a cross-member "c". Here's a picture: Just to be sure I ...
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0answers
35 views

Find the maximum force P that can be applied for which the blocks do not slide and their respective acceleration

Two blocks are on an inclined ramp of 35 degrees. Block A is on top of block B. Block A weighs 36 lbs and block B weighs 18 lbs. The coefficient of static friction between the two blocks is 0.45 but ...
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24 views

Linear thermal expansion from statistical mechanics?

I came across a question recently regarding work done by an expanding metal and the origin of the energy used for the work, and most of the responses pointed the person to look more at the enthalpy ...
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1answer
49 views

Working Out Shaft Torque in a Stirred Tank with a Cylindrical Cavern Formation (using a non Newtonian fluid)

Here is some background to the problem (in a stirred tank): "With yield stress non-Newtonian (viscoplastic) fluids, it is possible to generate an agitated volume around the impeller, defined as a ...
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3answers
199 views

Why is the definition of inertial mass circular?

On Wikipedia, the definition of inertial mass is: Inertial mass is the mass of an object measured by its resistance to acceleration. And, can be evaluated using $F = ma$, Newton's second ...
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4answers
91 views

Is torque necessary in rigid body mechanics? [duplicate]

Suppose we have a weightless, rigid rod fixed at one end, but free to swing at the other, where there is a mass $m$ attached. If we want to determine the tangential acceleration of the mass using ...
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0answers
21 views

Force by torque or force by speed with make the body jump?

I have a small object made of plastic weighing 3kg and I want to make it jump with the help of a dc motor and a plastic rod attached to it (4 such motor with rod are attached on the object at 4 ...
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4answers
92 views

Draw the Free Body Diagram

Question: Draw the Reaction Force at point P. My Attempt and Reasoning: Since the Reaction or the Normal Force is normal to the surface the solution according to me should be- However, the ...
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1answer
44 views

Related to pressure and force [closed]

If we made a thing like the one shown in the figure where the cross sectional areas of two piston heads are different and exposed to the same atmospheric pressure and the air between the piston heads ...
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3answers
110 views

If neutrons aren't affected by electromagnetic force, what causes it to bounce off matter?

Say a neutron is heading for a mountain, what would cause it to bounce off said amalgamation of matter? Electromagnetism is ruled out, gravity is too weak, (if I'm not mistaken) nuclear strong force ...
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4answers
309 views

Why do wheels spin?

I'm pretty sure this is probably a stupid question but it is annoying me a lot. In my physics textbook it says, cars move because the wheels exert a backward force on the ground and the ground exerts ...
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2answers
83 views

Why is the restoring force directly proportional to extension?

When deforming any spring the deforming force is always greater than the restoring force until equilibrium is reached. So, if a constant deforming force caused an extension in any spring the restoring ...
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1answer
31 views

Why isn't the entire force we apply on two objects transmitted to the second object?

When we exert a force of X N on a box in contact with another identical box on a frictionless surface, the resultant force on both boxes is 0.5X N. My question is, why doesn't the first box push the ...
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2answers
60 views

Rising glass in xkcd what if

In http://what-if.xkcd.com/6/, Around this time, the glass on the left starts to visibly lift into the air. The air pressure is trying to squeeze the glass and water together. This is the ...
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3answers
76 views

Why do objects with mass have gravitational force that is proportional to their mass?

Why do objects with mass have gravitational force that is proportional to their mass, i.e the larger the object the more gravitational force it has?
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1answer
35 views

Basic tension and equilibrium confusion

The following is what I did: $$Fsin\theta = 60 => F = 93 N$$ $$Fcos\theta = 40 => F = 52 N$$ Why do I get different results? Does this mean the object isn't in equilibrium? How can I ...
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0answers
37 views

Force on a charge due to charged sheet

I want to find the force on a positive charge placed at a distance $d$ from a positively charged infinite plate. Of course, it can simply be done by finding the electric field due the plate using ...
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4answers
94 views

Newton third law and collinearity of forces

I have a doubt on the formulation of Newton third law. When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction ...
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1answer
68 views

How to model analytical expression for spring constant $k$ for certain structure?

In the deflection of beam, I learned that $$ \delta y=\frac{FL^3}{3EI} $$ where $$ I=\frac{h^3w}{12} $$ Together they comprise $$ F=\frac{Eh^3w}{4L^3}\delta y $$ How do I apply to four beams? ...
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0answers
19 views

How to measure the properties of a non-newtonian fluid?

We have made non-newtonian fluid by mixing water (or Tonic) and starch. We can't figure out the link between the amount of water and starch and the viscosity of the fluid. What we can figure out is ...
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0answers
30 views

Superstring mass between 2 D-branes

The mass of a superstring between 2 parallel D-branes of dimension $p$ and $q$ is $$m^2=(N−a)+(y/2π)^2$$ But what is the value of the normal ordering constant $a$?
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1answer
28 views

Forces & Pressure

So, today I learnt that P=F/A. For something with a flat surface, it is easy to grab. Then came to my mind, how about the pressure exerted by a curved surface? How do you calculate the pressure? To ...
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2answers
45 views

Helium Lift Potential [closed]

A particular mass of helium is required to lift a particular weight. If the weight stays the same and the mass of helium is decreased can the same lift force be achieved by increasing the ...
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1answer
69 views

What is the difference between the Lorentz force and the ponderomotive force? [closed]

I understand that Lorentz force is due to motion of moving charged particle in a magnetic field, and I imagine that ponderomotive force is mechanical version analogy to a person surfing on a wave ...
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2answers
59 views

Dynamics: Forces in a closed system

I need help with the following question: There is painter in a crate which hangs alongside a building. When the painter pulls on the rope, the force he exerts on the floor of the crate is 300N. The ...
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0answers
39 views

Axial loaded bars problem

I completely disagree with the following calculations: Based on my understanding, there is no force either internal or external applied to the Green bar, so it should be 0N. The reaction (internal) ...
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2answers
71 views

Is polar coordinates frame non-inertial?

Consider the acceleration expressed in polar coordinates. $ \left( \ddot r - r\dot\varphi^2 \right) \hat{\mathbf r} + \left( r\ddot\varphi + 2\dot r \dot\varphi \right) \hat{\boldsymbol{\varphi}} ...
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1answer
38 views

In rotating frames, particles do not travel at constant velocity?

If we measure a particle's trajectory in a rotating frame of reference as $\vec x=\vec x(t)$, then $\frac{d^2\vec x}{dt^2}=0$ could be zero? I'm trying to explain why the Newton's first law of ...
0
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1answer
31 views

Explanation of a Mechanical Situation [closed]

The box sitting on the table top has some mass $m$ (I would refer to the weight of the box just as $\mathbf{W}$), and its net acceleration which I call $\mathbf{a}$ is zero, for the time being. This ...
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1answer
26 views

Structure of force table

In school, they asked us to do a force table and to search about it on internet to know what to do. The problem is that I searched for hours but I didn't understand the concept 100% since I am not ...
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0answers
38 views

What is the space-time medium? [closed]

What is the space-time medium? According to this answer: "... fields are a fundamental part of the universe." Then why do we describe a gravity as being depressions in space-time? And why don't we ...
1
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1answer
45 views

Force with different distance dependence

Recently, I have learnt about the central force motion. I came across some forces with different distance dependence, for example, k/r^2(common) one, k/r^4, or even the combined one k/r^2 + k'/r^4 (k, ...
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4answers
238 views

Normal force on vertical circular motion

I have a couple of questions concerning vertical circular motion. The object shown in the diagram moves with constant speed on the inside of a circle. In point A the normal force points to the ...
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3answers
36 views

Modelling an Airplane Question

For an assignment of mine I am creating a very basic model of an airplane, where I choose to consider a fixed amount of parameters that affect flight and to disregard others which I find too difficult ...
0
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1answer
55 views

Is a laminated padlock really stronger than a solid one, and if so, why?

I used to think that the padlock design of using many layers of metal stacked to form the main body was a cost-cutting consideration. This was my assumption before I came across the idea that it was ...
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2answers
50 views

Condition for a force to be conservative

I get that a force dependent on path is non-conservative or a force which does non-zero work in completing a cycle. But how do you prove that mathematically. Let's assume I have a force F= 2yi + ...
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3answers
102 views

How to explain the force applied on this object? [closed]

Sorry for posting such a simple problem but I'm having trouble understanding this concept. In the picture below, we have a force, $ \vec F_{app}$ acting on two objects, A and B. Mass of block A: $ ...
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4answers
1k views

What Keeps a Pendulum Moving In a Circular Path?

From the figure, we know that $F_{net} = mg\sin\theta$. Now, this force $\vec{F_{net}}$ is in the direction of the velocity $\vec{v}$ of the bob, both are tangent to the path. Therefore, the net ...