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

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24 views

The concept of displacement in definition of work

Suppose an ideal spring is attached to a wall at one of its end. Let an external force act on the spring at another end to stretch the spring to distance $x$. If spring constant is $k$ then work done ...
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2answers
107 views

Why is the potential energy for a body raised up by a height negative?

I tried deriving the potential energy of a body when raised at a height $h$ above the earths surface, using the formula: $$PE = -W_\text{conservative}$$ where $W_\text{conservative}$ is the work ...
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2answers
197 views

Force vs. impulse: what is the math description of their interaction?

In this image there are two forces acting on the same body, and we can decribe them mathematically and geometrically using vectors and the palallelogram rule. NOw, suppose the box (stone, ...
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1answer
35 views

When to use h = Cp∆T or u = Cv∆T

I'm getting myself confused on when to use h = cp∆T or u = cv∆T where cp is the specific ...
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1answer
35 views

Work needed to pump the balloons

Let's suppose that we want to pump the balloons underwater from the initial volume $V_0$ to the volume $V_1$. The pressure there equals $p_1$ and the atmospheric pressure is $p_0$. It is claimed ...
2
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1answer
22 views

How much power does it take to keep a massive particle suspended in a gravitational field?

For instance if I have a rocket of mass $m$ in a uniform gravitational field $g$, and I want to keep it floating in the air via thrust alone, then how much power in the form of (say) chemical energy ...
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2answers
35 views

Use Work-KE Theorem? [closed]

I've been trying so long at this problem to no avail. I drew my free body diagram, but I'm unsure which formula to use. Could someone help me out?
1
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1answer
112 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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0answers
22 views

How is the Joule normalised?

Apologies if this question is a duplicate, I tried searching for this question both on Google and here, but was unable to find an answer. A Joule is defined in various ways, some of them being: ...
2
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2answers
127 views

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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2answers
95 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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2answers
53 views

How this formula for work follows from the definition?

If a particle moves along a path $\gamma : I\subset \mathbb{R}\to \mathbb{R}^3$ then the work done by a force $\mathbf{F}$ is defined by $$W = \int_{\gamma} \mathbf{F} = ...
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1answer
29 views

Does the line integral definition of Work involve distance or displacement?

My textbook reports the following definition of Work: where ds is the infinitesimal displacement. I know that an infinitesimal displacement is usually denoted by dr and I also know that the ...
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6answers
135 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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2answers
68 views

If an object rests on a table, not accelerating, how much work do both the object and the table do?

Obviously, the net work done is zero, because there's no motion, but is the proper way to look at it that both the object's gravity and the table's normal force do zero work, or that one does positive ...
3
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2answers
56 views

Where does this formula for sagging of a beam come from?

In one of my physics textbooks there is a chapter on the elasticity of materials which contains pretty basic outline about Young's modulus, stress-strain, elastic potential energy and related stuff. ...
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1answer
35 views

Integral limits when calculating the work

If I integrate $$dW= \vec{ F} \cdot d\vec{\ell}$$ which are the limits? In $$\int\limits_{W_{inf}}^{W_{sup}}dW= \int\limits_{\vec{\ell}_{1}}^{\vec{\ell}_{2}} \vec{ F} \cdot d\vec{\ell}$$ it is ...
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1answer
26 views

Which is the right sign convention for the potential difference?

The circulation of the electric field gives the potential difference, but is it : $$V_B-V_A = \int_A^B\vec{E}.\vec{dOM} \hspace{1.5cm} (1)$$ or $$V_B-V_A = - \int_A^B\vec{E}.\vec{dOM} \hspace{1cm} ...
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2answers
95 views

Is work done in rolling friction?

I am confused by rolling friction. Suppose you have a cylinder rolling which starts at rest at the top of an incline plane and begins to roll down the plane without slipping. Is work done by the ...
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3answers
45 views

How work theoretically is zero, when person did do work while covering a distance then returning it?

$W = Fd$, meaning if a body moved a distance, say $3 m$, and returns, its distance will be zero and work will be zero. I do understand it mathematically and graphically but can someone explain it to ...
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2answers
256 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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3answers
46 views

Given Force in vector form, how do I find work done? [closed]

A force of $F=\hat i+2\hat j-3\hat k$ is applied to a particle that moves 10 meters in the direction of $\hat i+\hat j$. How much work is done?
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1answer
33 views

Meaning the symbol, $W$ and $dW$

What's the difference between $W$ and $dW$? They are both work done and have similar formulae (same dimension). But I don't know the difference between them. $dW$ here ISN'T power.
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2answers
60 views

Does inducing charge on a grounded conductor do work?

Imagine a grounded conductor as an plane of infinite area. If I bring a charge to a close proximity to the plane, it induces some charge distribution on the conductor. The question is: is any work ...
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0answers
28 views

How is $P = P_{ext}$ derived, for reversible processes?

I know that for a reversible process the inexact differential of $Q$ must be equal to $TdS$ because the total entropy of the universe must remain constant. Is there a way to formally derive that the ...
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1answer
32 views

Given an initial push, is work done on an object infinite in a hypothetical empty universe?

Consider a hypothetical empty universe containing a single object. Given an initial push, will the work done by the forever moving object be infinite?
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21 views

Work done against a physical field: positive or negative?

My understanding of signing conventions contextual to physical fields: With frame of reference as object: Work done by an object against a physical field is positive. Work done by a physical field ...
3
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0answers
48 views

How much work can a single grain of rice do? [closed]

I found a website saying a grain of rice contains 1/10 kcal. I'm not a physicist and haven't done maths for a long time. But here's what I came up with: E = m * g * h One small calorie equals ...
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1answer
99 views

Violation of conservation of energy… or not? [closed]

The work done by surface tension is double the increase in potential energy. This is a clear violation of conservation of energy. What is the flaw here? Work done by surface tension is \begin{align} ...
0
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1answer
27 views

Why the gravitation potential in a uniform field has negative values?

As we know the gravitational potential is the work done per unit mass in taking a point mass from zero potential (at infinity distance) to the point in a gravitational field. But why the work is ...
0
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4answers
60 views

Using formula for work with distance of 0m [duplicate]

Consider this: Wind is pushing a huge rock towards me at with massive force at 2m/s. I push against the rock at equal force so the rock stays still. I am clearly "working" very hard, using a lot of ...
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2answers
33 views

If I throw a ball horizontally, what are laws, related to Work-Energy concepts, governing that all the situation? [closed]

In a book, A textbook of physics, There was a statement that when we see a motion of body and start to count the laws related to energy-work concepts governing that motion, we at once find ourselves ...
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1answer
46 views

Newton's third law of motion versus Work

Newton third law of motion says that "To every action, there is always an equal and opposite reaction". The vector study tells us that if two vectors are of same nature and equal magnitude but ...
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1answer
41 views

Does $\delta W=pdV$ hold for non-ideal gases

I have that for quasistatic processes, $$ \delta W= \textbf{f}\cdot d\textbf{x} $$ so for a gas $\delta W=pdV$. Does this only hold ideal gases or will it hold for van der waal's gas?
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3answers
3k views

Proof of conservation of energy?

How is it proved to be always true? It's a fundamental principle in Physics, that is based on all of our currents observations of multiple systems in the universe, is it always true to all systems? ...
1
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1answer
22 views

Is Energy said to do work on the body it is stored in?

Assume a boy on top of the hill, his $potential$ $energy=mgh$. He mostarts to move without pedalling the cycle so is that work being done on it due to the conversion of Potential into Kinetic Energy ...
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5answers
41 views

Who is said to do Work, me or the body?

If I subject my force to a body and it is displaced then the work is said to be done. What is that work done by? Is it said to be done by me or that body?
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2answers
26 views

Do transferring energy and applying force to a body imply same?

Do transferring energy and applying force to a body imply same meaning? When we say, "I throw a ball using my pushing force so on the other hand, can I say that I transferred my kinetic energy to the ...
2
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2answers
68 views

What is the meaning of the negative sign in $W = -\Delta U$?

What is the meaning of the negative sign in $W = -\Delta U$ ? As far as I understand, $W = -\Delta U = -(U_f - U_i) = U_i - U_f$. While $U_i$ is the initial potential energy (before applying the ...
0
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2answers
129 views

Proof that the electric field is conservative

I was told a proof that the electric field was conservative (without using $\nabla$) which used a point charge and showed the following: $$w.d.=\int_c{\vec F \cdot \mathrm{d} \vec l}=\int_c{\vec ...
1
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0answers
34 views

Why is no work done by magnetic forces in a uniform B and E field (perpendicular to one another)?

Say $B$ points in the $x$ direction, and $E$ points in the $z$ direction. Assuming a charged particle begins at rest at the origin, its motion will be a cycloid that progresses indefinitely in the ...
2
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2answers
2k views

Does moving something horizontally in gravity do no work?

Bill’s job is to lift bags of flour and place them in the back of a truck, which is parked next to him. Sally is loading the same bags of flour into a similar truck that is located 10 m away. ...
0
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0answers
33 views

How to tell direction of work

I think of direction of work as relative to direction of motion, but I got a question of a parabolic ball throw asking the direction work done by gravity and friction over the entire parabola. Since ...
2
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2answers
32 views

Work done in lifting chain with nonuniform linear density

I am teaching calculus, and a natural-seeming problem type just occured to me. It would go something like: a 2m chain hangs from the top of a building. Its density at a point h meters from the edge ...
11
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6answers
2k views

How can energy be useful when it is 'abstract'?

The topic which haunted me for two years until I gave up on it. But now I am doing engineering and this topic suddenly popped out of my textbook from nowhere. I seriously need to understand this topic ...
3
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3answers
147 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 ...
1
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1answer
23 views

Issue with Work-Change in KE equivalence

First-year physics student, with a pretty basic question. I've seen proofs that Work = Change in Kinetic Energy involving calculus, and they make sense to me, but I'm not sure why the following, much ...
7
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2answers
29k views

Conceptually, what is negative work?

I'm having some trouble understanding the concept of negative work. For example, my book says that if I lower a box to the ground, the box does positive work on my hands and my hands do negative work ...
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4answers
772 views

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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3answers
62 views

Work power and energy

When you push your bicycle up on an inclined the potential energy of the bicycle and yourself increases. Where does this energy come from?