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

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Frictional torque=? [on hold]

A uniform, hollow, cylindrical spool has inside radius $R/2$, outside radius $ R$, and mass $M $ (see figure below). It is mounted so that it rotates on a mass less horizontal axle. A mass m is ...
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0answers
44 views

Why do we integrate in the following derivation? [on hold]

Electric potential due to a point charge. Let a point O have charge $q$ at a distance $x$ from point A and at a distance $r$ from point P ($r<x$). Suppose a test charge $q_1$ is placed at A force ...
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6answers
104 views

Why does positive work done by internal conservative forces $\implies$ decrease of potential energy?

Potential energy can be thought as the amount of work that the force can potentially do on the point because of its position. $$W=-\Delta U=U_{initial}-U_{final}$$ A positive work done by a force ...
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2answers
29 views

Work and energy example [duplicate]

The normal definition of Work, as far as I have read, is: Energy is transferred through work. But I just heard an educationist state this example, where there is a weightlifter who keeps up a huge ...
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3answers
93 views

Is reversible work a point function?

The potential of a conservative force is equal to the reversible work done on or by a system. But since the potential of a conservative force is represented by a point function, this would seem to ...
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3answers
127 views

Work done by an ideal gas expressed as change in potential energy of fluid

I get confused in problems where it is necessary to evaluate the work done by a gas that someway moves a mass. I'll make an example. Consider the tube containing mercury and an ideal gas in A (...
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2answers
103 views

Work energy theorem explanation

So there is this problem in my head, it may seem very simple, but I need an answer. The problem is, we have some object, and we apply a force by our hands with a constant speed from a position (1) to ...
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1answer
56 views

Mechanical equivalent of heat => transfer from work W to heat Q

Consider the following experiment to determine the mechanical equivalent of heat $\mu = \frac{\Delta W}{\Delta Q}$ Not seen in the picture is a weight with known mass hanging down the cord. When you ...
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3answers
45 views

Work done on gas problem with movable set

I found two different version of an exercise where the work is considered in a different way. Consider a gas in a tank divided in two parts by a movable set. The set in $B$ is also movable. If a ...
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1answer
66 views

What is meant by a “change in volume of a system”?

I keep getting confused when my professor talks about the change in volume of a system. Sometimes it seems as though he's talking about the volume of the gas and at other times he might be talking ...
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2answers
84 views

Rotational work and forces such as static friction or ropes tension

I'm confused about the rotational work, defined as $W=\int_{\theta_1}^{\theta_2} \tau_z d \theta $ Where $\tau_z$ is the component of the torque parallel to the axis of rotation $z$. Consider a ...
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1answer
35 views

Work by spring force

To calculate work done by general force, apparently we have integral like the following: $W=\int_{s_1}^{s_2} F(s)\,ds$ But why when it comes to the spring, it is not $W_{s}=\int_{0}^{s} Fs\,ds=\int_{...
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2answers
57 views

Dissipation and first law of thermodynamics

Consider the following situation: a certain gas is contained in a well-insulated cylinder with a well-insulated piston head. Now, in this case the piston is not frictionless. In order for the piston ...
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4answers
1k views

Is work done = change in KE, or change in mechanical energy?

Starting from $F = ma$ we get: $$ F=m\frac{dv}{dt} = m\frac{ds}{dt}\frac{dv}{ds} = mv\frac{dv}{ds} $$ which leads to the work done: $$ W = \int Fds = \int mvdv = m\frac{v^2}{2} - m\frac{u^2}{2} \...
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3answers
289 views

Work and free body diagrams

I am a bit confused with how to find work when there is a free body diagram. I am trying to work out this problem, and in it a box is being pulled at a constant speed by a rope at a constant angle ...
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1answer
30 views

There is a system of 2 electrons approaching each other.Want to know how the system gained the potential energy? [closed]

Well there is a system of 2 electrons approaching each other with a velocity 'u'. The question here is to find the closest distance of approach, r after which they start moving in opposite directions. ...
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0answers
28 views

Joule's “Work-Heat Equivalent” Experiment

I have been reading about the Joule's experiment that is supposed to have shown that work is the equivalent of heat. I can't really find the original paper and I am finding trouble understanding how ...
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0answers
15 views

Calculating the amount of work done for a bench press movement? Is this a reasonable conclusion?

Me and a friend have been working out for some time and have been bench pressing each weak, increasing our weight. Once we started getting to heavier weight we noticed that he was able to get more ...
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2answers
42 views

Relation between field and Potential energy of a body

I have read that if a body is in a field and is 1. moved in a direction opposite to the direction of a field, its potential energy increases.But why does it increase? 2.Also, if we move the body in a ...
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4answers
59 views

Is this thought regarding work and potential energy correct?

I am really confused about this. The potential energy acquired by an object is equal to $mgh$, if we are on any planet, where $g$ is the planet's gravitational acceleration, which directly comes from ...
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1answer
34 views

Work done relation to potential energy

I know work done is negative of change in potential energy, I.e., $W=-(∆U)$. It means that Work done against a force (or work done on a system) increases its potential energy. And Work done by a ...
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3answers
105 views

Dealing with negative work

Dumb question, I'm working with vector fields right now, and one question on here tells me to assume an object can take on three paths from a to b. (paths not listed here) for times in [0,1] Now ...
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3answers
63 views

An object is accelerating on a rough surface with frictional force of 10N. Is the friction doing any work on the object?

This question might look stupid to some but I am in great confusion. An object, say a box, is moving on a surface with some velocity v and is accelerating. It means that the force applied by the box ...
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2answers
45 views

Negative work leading us to negative energy [closed]

We know that energy is the ability to do work and we know that the work can be negative as cos theta of the angle in which force is applied can be negative. Moreover we take the units of work and ...
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4answers
243 views

How to calculate the work of the electrostatic forces in a parallel-plate capacitor?

The expression of the energy stored in a parallel-plate capacitor is: $$U = \frac{e_0\cdot A \cdot V^2}{2d}$$ with $e_0$ the vacuum permittivity, $A$ the surface of the capacitor, $V$ the applied ...
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2answers
53 views

Virtual Work- Is the presentation in Cornelius Lanczos wrong?

Book: The Variational Principles of Mechanics by Cornelius Lanczos Edition: 4th Chapter: 3, The Principle of Virtual Work I am on the second page of the 3rd chapter (pg 75; it has the Eqn. 31.1). ...
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3answers
34 views

Need help with signs (+ -) in electric potential work and potential energy problem

The problem is from Sears and Zemansky's University Physics, 12th edition in Spanish. The problem says: How much work is needed to assemble an atomic nucleus that contains three protons if it is ...
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2answers
80 views

I'm learning Work-energy theorem, this question popped into my mind about Force applied and displacement [closed]

I know a lot but I'm not sure, I'm guessing if 400 J of work done on a 800 Newton object, if I'm correct, 400 N to 800 N... that is 0.5 m displacement, so by $W = \Delta \ KE$ why do I get 200 J? I ...
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1answer
33 views

Conservation of mechanical energy when object strikes the ground

When I raise a pen, the external work I do gets stored in the form of potential energy hence the mechanical energy is increased. When I leave the pen the pen starts falling and as the potential energy ...
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3answers
152 views

Does the work done by a person equal the work done on the object in this situation?

If you applied a constant force over a floor that has friction on an object, would the work done by the person equal to the work done on the object? Assume that the floor is flat and that the object ...
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6answers
566 views

How can tangential acceleration from a radial force be explained?

A mass is attached to a rope, and put into a circular motion. If I pull the string from the center, the tangential speed of the mass will increase (by conservation of angular momentum). I am ...
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3answers
259 views

Potential energy of springs and gravity, and work of a force

I am currently really stuck on this problem and I am not sure how to actually solve it, I think I can reason it out logically but I do not know how to show it. Here it is and under I will show what I ...
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2answers
68 views

Work done according to Newton's Principia

Actually I was going through the principia, reading Newton's derivations of the properties of ellipses. Suddenly I had this question which got stuck in my mind - Throughout Principia Newton uses the ...
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3answers
695 views

Is net work and total work same?

According to my text book Total Work = Delta Kinetic Energy = KEf - KEi But then work is defined to be dot product of Force (vector) and Displacement (vector). Also to my knowledge work is ...
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2answers
515 views

Work done by battery and potential energy of a capacitor

I have a doubt about the work done by a battery and the potential energy of a capacitor? 1- Consider a circuit where the capacitors are connected to the terminals of a battery. Through calculations ...
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4answers
64 views

Is the concept of work only defined in mechanics?

I'm studying energy and work, so far it looks like work only makes sense in kinematics (objects that move), but energy makes sense in many other ways (electric, thermodynamic, mechanic). Is work a ...
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3answers
83 views

Is this definition of work right?

My thermodynamics textbook defines work as follows. Work is motion against an opposing force. But this definition of work doesn't imply that work is done in accelerating a body does it? So is ...
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3answers
68 views

What is the relation between Force, Physical Strength,Enery and Work?

I am sorry ,but, I am not much of science or a physics guy, if this question sounds stupid. Anyways, what is the relation between all of them. Like for example, does applying more force means more ...
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1answer
139 views

Work done by friction on a body?

I know that when a body slides over a surface, the work done by friction is not stored as potential energy in the body. It is dissipated in the form of heat. But why is it not stored as potential ...
8
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5answers
16k views

Why does work equal force times distance?

My 'government-issued' book literally says: Energy is the capacity to do work and work is the product of net force and the 1-dimensional distance it made a body travel while constantly affecting ...
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2answers
64 views

Problems with work on an inclined plane

A constant force $F_a$ of magnitude $82.0N$ is applied to a $3.00 kg$ shoe box at angle $53.0^{\circ}$, causing the box to move up a frictionless ramp at constant speed. How much work is done on the ...
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2answers
60 views

Why does the sign of Delta H indicate whether the reaction is exothermic or endothermic?

If $\Delta H = Q + W$ (assuming constant conditions), then there are two terms involved in calculating $\Delta H$, only one of which measures heat gained/released. It is possible then for $\Delta H$ ...
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1answer
19k views

How much work is needed to compress a certain volume of gas?

I want to know the formula (and what does the symbols stand for) for how much work is needed to compress a certain volume of gas?
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4answers
45 views

How can removing energy from a system do work? (ice)

Water freezing into ice expands, damaging roads, breaking rocks, etc. To my understanding, this is doing work (in a physics sense) by removing energy from the system. How is this possible?
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1answer
39 views

Thermodynamics: efficiency of a heat engine [closed]

How can we calculate efficiency of a real heat engine? Do we have to consider volume of an object while calculating efficiency? Like in this question If so, how we have to proceed? Thanks in ...
1
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0answers
39 views

Why we can use partial derivatives to tell if a force is conservative? [duplicate]

Let us, initially, analysis only a two dimension situation. Assume that $F(x,y)$ is a force dependent on the particle position (give by $x,y$) is proposed that if \begin{equation} \frac{\partial \...
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1answer
27 views

Why is force negative if PE increases?

I'm looking at the PE vs force graphs for gravity, and it doesn't make sense to me. As potential energy increases (and the object goes higher above the ground), F=-mg. But if I'm raising an object up, ...
2
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1answer
61 views

Work done in bringing down a body [closed]

A block of mass $30$ kg is being brought down by a chain. If the block acquires a speed of 40.0 cm/s in dropping down $2.00$ m, find the work done by the chain during the process. I have calculated ...