The product of the force on an object and the displacement the object undergoes along the direction of the force.

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Sign of Work and potential energy in electrostatics

Conceptual question: Suppose we have a configuration of point charges. If the potential of the energy of the system is negative, this means work is positive. I'm kind of rusty with my mechanics, ...
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3k views

Is any work done if I walk in a circle?

My friend and I were arguing about this and I was wondering if someone out there could settle this for us. Basically, he and I were walking to buy some stamps. When we were on our return trip he ...
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394 views

What does it mean to say work is path-independent when pushing an object in different directions?

If I apply a straight upward(perpendicular to ground) force against gravity of $5\ \mathrm{N}$ and lift an object "A" 10 meters, then the work done is: $$ W = F \times S = 5\ \mathrm{N} \times 10\ ...
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320 views

When can one write $a=v \cdot dv/dx$?

Referring to unidimensional motion, it is obvious that it doesn't always make sense to write the speed as a function of position. Seems to me that this is a necessary condition to derive formulas ...
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97 views

Source of energy for magnetic work?

I set two magnets on my desk such that they are experiencing attraction to each other, but due to friction with the desk, are just outside of the distance where they would snap to each other. Then I ...
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342 views

What's wrong with my derivation for the spring constant? [duplicate]

An $8.00\ \mathrm{kg}$ stone at rest on a spring. The spring is compressed $10.0\ \mathrm{cm}$ by the stone. What is the spring constant? I used conservation of energy to solve this problem. The ...
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Is any work done when I walk?

I am trying to figure out the amount of work done when I walk X miles or for X minutes. So I got Work=Force x Distance and Force=Mass x Acceleration and Acceleration=(change in velocity)/time. I am ...
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Why is the maximum work achieved in reversible processes?

Let us consider an ideal gas. Let it be present initially in a state $(p_1,v_1,t_1)$. Now let it be driven to another state $(p_2,v_2,t_2)$. Why is it so that during this process the maximum work can ...
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222 views

Work done on stationary rocket

Suppose I have a rocket thats exerts a force (with negligible loses in mass), which cancels out the downward force of gravity. Clearly my rocket could be moving at a constant velocity (ignore air ...
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246 views

Why does it require such little energy to create the fastest thing in the universe?

I have noticed when I turn on the light switch in my house light comes from the bulb. How is this light created?(process occurring in the bulb) and why is this small amount of electricity enough to ...
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3k views

Work done by the Magnetic Force

The magnetic part of the Lorentz force acts perpendicular to the charge's velocity, and consequently does zero work on it. Can we extrapolate this statement to say that such a nature of the force ...
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105 views

Relativity of Work

Let's say there is a man pushing a wall with a force of $-1 \text N$, and moving it $0 \text m$. Since $W = F \cdot d$, he has done $0\text J$ of work on the wall. Another man is pushing a duck with ...
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226 views

Work performed by a stationary object in a gravitational field “on Earth”

I was thinking about this problem: How much work is required to hold an object stationary in a gravitational field? or: How much energy is required to keep an object stationary in a ...
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176 views

What exactly is ''electric energy''?

If the two fundamental types of energy are kinetic and potential energy, is electric energy simply the kinetic energy of charge carriers? Also, is the statement "A cell converts chemical potential ...
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992 views

I have a slight problem understanding the concept of “work”?

What I understand is that work is not the same as a car using gas or a crane lifting a car high up into the air. Let's use the crane as an example. And let me write out a few lines from the book. ...
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472 views

Does a magnetic field do work on a moving rod?

In a case such as this one, my textbook says that I might be tempted to think the magnetic force is doing work (against the moving rod). It then says this isnt the case because "charges move ...
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4answers
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Paradox- Object thrown parallel to the ground will never fall down

Suppose an object is thrown parallel to the ground. The gravity acts downward (ie. perpendicular to the direction of motion of the object). The work done by gravity on that object will be given by : ...
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714 views

Why can't a magnet change a charged particle's speed?

I know that magnetic force acts perpendicular to the direction of the original velocity, so the velocity in that original direction is unchanged, but once the magnet starts acting, the particle's ...
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4answers
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Is the work done walking up an escalator in the same speed and opposite direction of the escalator zero?

Work equals force times distance, but what about walking up an escalator in the same speed and opposite direction of the escalator? In the frame of the ground, the distance is zero so the work must ...
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397 views

Potential Energy Concept

Imagine a book that we lift it with a force that is exactly equal to the force of gravity so the forces cancel out and the book moves with a constant velocity. Consider the situation after the book ...
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How can a magnetic field accelerate particles if it cannot do work?

A varying magnetic field can accelerate charge particles, but it is said that a magnetic field can't do any work so it should not be able to speed up charged particles, right? How is this apparent ...
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3answers
149 views

Work done changes between reference frames?

(This is not homework; a friend shared with me this puzzler and neither of us can figure it out.) Suppose you are in a plane traveling at velocity $v_1$ relative to the ground. The flight attendent ...
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5answers
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A force is exerted on a body, kinetic energy increases but no work is done by the force. Why?

After reading the article, I was totally perplexed . I was reading the External forces and internal energy transfers in Principles of Physics by Resnick,Halliday,Walker. It goes like that An ...
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Why work is a scalar and not a vector?

Work (in physics) is a scalar, but why? And why not a vector?
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972 views

Is energy expended when a force is exerted on a object? [duplicate]

Energy is expended when a person exerts force on a object. 1) From the equation Work Done = Force x Distance, if a force is exerted, but no distance moved, then no work is done. Hence, the statement ...
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Why can't the work done by a non-conservative force be zero?

Why can't the work done by a non-conservative force be zero? The displacement along a closed path is always zero. So, whatever be the type of force, variable or constant, the work has to be zero. Why ...
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Why doesn't static friction decelerate a rolling body?

I know that static friction isn't the cause of deceleration of a rolling body. But if static friction is the only force in the horizontal direction, then shouldn't there be some acceleration produced ...
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487 views

Is my textbook teaching an incorrect concept of Work?

I fear my textbook is teaching an incorrect concept of Work. I am very frustrated right now since I was struggling to understand the concept in the way that was explained in the textbook and my ...
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317 views

Can infinite work be done?

Wikipedia defines work as follows. In physics, a force is said to do work if, when acting on a body, there is a displacement of the point of application in the direction of the force. Also work ...
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630 views

Validity of work-energy theorem in presence of non-conservative forces?

How can the work-energy theorem be valid in presence of non-conservative forces since conservation of energy is not there?
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4answers
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Can internal forces do work?

My Mechanics textbook claims that the sum of the work by internal forces is not generally zero. translated to English the paragraph reads: Notice about the work by internal forces: the work by ...
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586 views

Find work done by force along a path - is parameterization the only way?

$F = x^3y^4 \hat i + x^4y^3 \hat j$ from $(0,0)$ to $(1,1)$. I am given different paths. For example, "first along x axis and then along the y axis" is one of the paths. Is this problem solvable ...
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78 views

Confusion with $F=-\nabla V$, $F$ conservative

I am rather confused by the relationship $F=-\nabla V$. If a pen drops from a height it loses potential energy so $\nabla V$ is negative. From the above equation this means that the gravitational ...
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394 views

What is the mathematical definition of work?

I'm looking for the pure mathematical definition of work, but I haven't yet learned line integrals. My book says that the work due to a force ${\bf F}$ from point $A$ to point $B$ is $$ W= |AB|\cdot ...
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135 views

The lab have a constant electric field and a constant magnetic field, what is the electric and magnetic field inside a conductor and far from it

The following is an old question from an exam in a Physics $2$ course I am taking, I have tried to solve the question and after I thought I got the answer I looked at the solution and saw it isn't ...
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3answers
367 views

Problem in understanding the Proof of $PV^{\gamma}$ =constant in thermodynamics

I have looked at the proof of this relation $PV^\gamma = C$; (where $P$ is pressure and $V$ is volume) in quite some places but I am not able to understand the logic behind the third step. In ...
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1answer
72 views

Help understanding work

I have this problem: An object with 800kg mass is lifted up 2.4m by a force $F$. How much work does the Force do on the object (gravity is the only other force acting on the object)? From what ...
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2answers
835 views

Understanding relationship between work and energy

I've read over 10 books about work and energy, and I just simply can't understand it. First of all, they go ahead and randomly define that work is force times distance: $$W=F X \cos\theta$$ Okay, ...
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820 views

Definition of force, kinetic energy and momentum

I've edited the post. Q1 and Q4 are the important ones but I didn't delete Q2 and Q3 since some older answers would not make sense anymore. To begin with, the formula of the kinetic energy $T$ is ...
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1answer
159 views

Work done by vibrating string

figure from http://webusers.physics.illinois.edu/~m-stone5/mma/notes/amaster.pdf The string has fixed ends, a mass per unit length of $\rho$, and is under tension $T$. This source claims that "the ...
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589 views

How to reconcile the two definitions of work? (mechanical and thermodynamical)

When studying classical mechanics, work is defined as: $W_M=\int F_{tot} \hspace{2 mm} dx$. However, for thermodynamics, work is defined as: $W_T=\int -F_{ext} \hspace{2 mm} dx$. I'm having trouble ...
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383 views

Work done by gravity on Water

Now according to me we would see change in potential energy of system and equate it to the work done by gravity. But when we see this the first column lowers by $H/2$ and right one rises by $H/2$ ...
3
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1answer
2k views

Area under a $pV$ diagram

What does the area under a Pressure volume diagram equal? I read in my textbook it equals 'external' work done, but why is this? First of all, what exactly is external work? Can you get it ...
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1answer
128 views

Could $\int (\ddot\phi + \mu\dot\phi^2)d\phi$ ever be negative? How to show it?

I am working on the following problem: Given a mass $m$ at rest at the base of an incline surface shaped like 1/12th of a circle with radius $R$. The mass is pulled up the incline by a rope that ...
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2answers
5k views

Work done by isothermal expansion from two different viewpoints

Consider an adiabatic system as follows. It consists of a gas in a container and a piston. Initially, the system is at equilibrium and the gas inside it occupies a volume $V_i$ at a pressure $p_i$ ...
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3answers
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Work done by Lorentz Force in case of motional emf

In the classical example of the slidewire generator where the rod slides on a U-shaped conductor in a magnetic field, we get a charge separation due to the Lorentz force. The way the induced emf is ...
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181 views

How can magnetic fields have energy and yet be unable to do work with that energy? [duplicate]

Magnetic fields can't do work. However, we use the following equation to describe the energy density of a magnetic field. $u = \frac{B^2}{2\mu_0}$ The term energy density suggests that the magnetic ...
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3answers
281 views

Line integral definition of work clarification

So I am kind of confused about the role of force when calculating work. Specifically, when defining work using a line integral. There is a paragraph in my calculus book that is really throwing me off ...
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2answers
120 views

Is the coefficient of restitution frame independent and energy conservation?

In this question I am ignoring relativistic effects. The following statements I think are true: change in Kinetic energy is not invariant under change of frame Force is invariant under change in ...
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798 views

How to calculate wasted energy

Suppose you are pulling a weight along a track at an angle (in the picture 45°). If the object is dislocated by a distance $D_{45}$ let's assume that the mechanical work done on/energy transmitted to ...