What is Work: Definition and 1000 Discussions

In physics, work is the energy transferred to or from an object via the application of force along a displacement. In its simplest form, it is often represented as the product of force and displacement. A force is said to do positive work if (when applied) it has a component in the direction of the displacement of the point of application. A force does negative work if it has a component opposite to the direction of the displacement at the point of application of the force.
For example, when a ball is held above the ground and then dropped, the work done by the gravitational force on the ball as it falls is equal to the weight of the ball (a force) multiplied by the distance to the ground (a displacement). When the force F is constant and the angle between the force and the displacement s is θ, then the work done is given by:




W
=
F
s
cos


θ



{\displaystyle W=Fs\cos {\theta }}
Work is a scalar quantity, so it has only magnitude and no direction. Work transfers energy from one place to another, or one form to another. The SI unit of work is the joule (J), the same unit as for energy.

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  1. C

    I Work done by a non constant force over a non constant angle

    I was just wondering if I needed to set up this double integral or not. I've never seen anywhere people setting up double integrals for calculating the work.
  2. amandela

    Work Done and Acceleration (Mistaken Answers?)

    So for Q1, I answered down (towards Earth) but the solution says there is no acceleration there. For Q2, I answered mgh, but the solution says it's mgh/t, which is power, right? I just want to make sure I'm not super confused. Thank you.
  3. Z

    Understanding work in translation and rotation of a magnetic dipole

    these notes on magnetic field from MIT OCW's 8.02 course. There is the following snippet on page 10 At this point it is still not clear to me exactly what a magnetic dipole is. I've done all the calculations for a current-carrying rectangular loop, so I will assume that a magnetic dipole is...
  4. dcmf

    Find net external work of a system w/ 2 objects w/ opposite forces

    A diagram is also provided, which looks like this: I'm not sure what is correct and after doing some digging online I still haven't been able to come to a consensus. I'm currently stuck between one of two possibilities: positive or zero. I'm pretty sure work on A (Wa) and work on B (Wb) are...
  5. Ineedhelpwithphysics

    Sign of Work (Negative or Positive)

    Im confused I did 850*9.8*14.7 = 1.2x10^5 Why is it not negative since the force is opposite to the motion?
  6. Ineedhelpwithphysics

    Work Pulley Problem with constant speed

    For A the 1.2 kg block is being pulled by gravity hence work is done downwards which will make work positive since it's going with the same direction as the force. 1.2 * 9.8 = 11.76 N pulled downwards Work = F*d 11.76*0.75 = 8.82 J The tension is the other force and since the thing is...
  7. Z

    Change in closed system energy with both conservative and non-conservative forces

    Thus $$\Delta K=-\Delta U + W_{nc}$$ $$W_{nc}=\Delta K+\Delta U=\Delta E_m$$ My question is about the following statement The system is closed. ##\Delta E_{system}## does not necessarily have to be zero. Where does (1) come from?
  8. Klaus3

    I Power done by work on a continuous body isn't the derivative of work?

    The definition of work and power done over a continuous body is: $$ W = \int Tn \cdot u dA + \int b \cdot u dV $$ $$ P = \int Tn \cdot v dA + \int b \cdot v dV $$ ##T## is the stress tensor, ##b## is the body force, ##u## is the displacement vector, ##v## is the velocity, ##n## is the normal...
  9. I_Try_Math

    Work done by friction on a hockey puck

    The answer key claims the answer is -0.9 J. By my math it should be -0.501 J, is that incorrect?
  10. MatinSAR

    Question about the thermodynamic temperature scale

    My first problem is to find the absored and rejected heat. Can I say that it is equal to the work done in an isothermal proccess (##dQ=Pdv##)? My reasoning : We have ##dQ=C_V d\theta + Pdv##. For constant temperature it becomes :$$dQ=Pdv$$
  11. walkeraj

    I The classical concept of work in a QCD context?

    Question: Is it meaningful to think of the repulsion of mutual color charge and the attraction of three different color charge in QCD as being indicative of the classical concept of work taking place? Exactly, how is this explained in the context of three charges needed to elicit the...
  12. clueless_roboticist

    I Work done along a path: how does velocity play into it?

    To boil down the question, if you have a body at rest and apply a constant force, it will accelerate and the work done on it will be F*s (or the integral version of that statement). However, as the body accelerates due to the force, does that mean, per a given time unit, more and more work will...
  13. D

    I Derivation of the Work done by spring force -- why do we substitute the force magnitude?

    i'm copying from the book... Hookes Law - F = -kx W = Fdcos∅ since ∅ is 180°, W = -Fd = -Fx W = ∫(-Fxdx) now the book says, from Hookes Law equation "the force magnitude F is kx. Thus, substitution leads to W = ∫(-kxdx)" why are they saying to substitute the magnitude of the force and not the...
  14. P

    Conceptual misunderstanding in applying formula for work done in adiabatic compression

    I was trying to solve a JEE ADVANCED 2020 paper 1 question 13 on thermodynamics. I attempted the problem and got a different answer than they did. I did it in a different way, but I can't find a mistake in both methods. So now I am stuck. I think the problem is in the first step probably using...
  15. M

    A Work done during adiabatic expansion on piston

    Does the work "extracted" from a gas (with the same initial properties) against a piston while expanding change based on the mass of the piston? For example, I have a specific volume of compressed air inside a cylinder with a piston positioned horizontally with stops. The air temperature is...
  16. A

    Is enthalpy just the sum of internal energy and work against external pressure?

    This was the question This is my solution The problem arose after reading this post on PhysicsSE and this answer given So If I remember correct work done is ##-P_{ext}\Delta V## I don't understand why $$\Delta H=\Delta U+(5×4-1×10)L.atm$$ If that answer (the answer on the PSE post) is...
  17. S

    Find the amount of work done against gravity in moving a 150kg rocket

    I started by calculating the energy at the Earths surface, which is just -G(150)(6 x 10^24)/(6400 x 10^3) = -0.9 x 10^10, and calculating the energy at the orbit radius, E = -G(150)(6 x 10^24)/(18000 x 10^3) = -3.4 x 10^9, then doing some subtraction we have -3.4 x 10^9 - (-0.9 x 10^10) = 5600 x...
  18. biomajor

    Would one be pushing as much as their weight?

    Because one is effectively pushing in the same way as a chest press machine, wouldn't the work done be the same?
  19. elijahmiles

    Ok

    HI, I need help wtih my physics work and dont know where to ask
  20. Z

    Work done during quasi-static, isothermal expansion from P_i to P_f

    I am posting this question after I thought I had easily solved the problem, but then when I checked the back of the book I saw that I was incorrect. Here is what I did. (a) $$W=-\int_{V_i}^{V_f} PdV\tag{1}$$ $$V=V(P,T)-\frac{nRT}{P}\tag{2}$$ $$dV=\left ( \frac{\partial V}{\partial P}\right...
  21. mazia

    Questions Regarding a Cat Going Up a Ramp

    EDIT: I've finally found the solution, so here's what I did. First, calculate Work using the equation: (F-mgsin(theta))*displacement, where F=the force being applied by the push, theta is the angle of the ramp, and displacement is the length of the ramp. Now that you have the value for work...
  22. Z

    I Is it accurate to say work is motion against an opposing force?

    Is the following quote accurate: "The fundamental property in thermodynamics is work: work is done to achieve motion against an opposing force" Specifically, I am asking about the portion after the colon. I am a little confused by the notion of an opposing force. Let's say we are in outer...
  23. A

    Work done during a collision -- Change in Kinetic Energy & change in Momentum

    Hello guys, I need help on this problem, "You throw a ball with a mass of 0.4kg against a brick wall. It hits the wall moving horizontally to the left at 30 m/s and rebounds horizontally to the right at 20m/s. (a) Find the Impulse of the net force on the ball during its collision with the wall...
  24. physicsmaster123

    Work done by gravity on a car rolling down a hill

    I tried E =Fxcos0 but only ended up with 243kJ
  25. E

    Work done by non-conservative force while particle moves in circle

    I have to show that the force is non-conservative, i.e. that work done for the round trip ##\neq 0##. Rearranging the circle equation, I can say that:$$x = \sqrt {R^2 - y^2}$$$$y = \sqrt {R^2 - x^2}$$ Then I have:$$F_x = -\sqrt {R^2 - x^2}$$$$F_y = \sqrt {R^2 - y^2}$$ Now, as I understand it, I...
  26. E

    Signs of work done and delta K.E.

    I'm asking about this with particular reference to the signs of the answers. Here is the question: The answers in the back of the book are: (a) ##1.2 \times 10^4 \text{ N}## (b) ##39 \text{ m}## (c) ##4.7 \times 10^5 \text{ J}## (d) ##4.7 \times 10^5 \text{ J}## Here's a rough sketch of...
  27. E

    I Confusion on Callen's Maximum Work Theorem

    This question was, effectively, asked here (please refer to that question for additional context); however, I don't think the given answer is correct (or at least complete) despite my having added a bounty and having had a productive discussion with the answerer there. In particular, I don't...
  28. singularcell

    Efficiency and Temperature in Heat Engine Cycles: Approaching Parts B, C, and D

    I didn't have much trouble with part a but I'm struggling with b,c, and d. I considered the efficiency formula for a heat engine e = work done by engine/ qh but i am unsure of how to approach it. for part c) not sure how i can get to Tc without knowing Th for d) my gut is telling me 5/2 but i...
  29. D

    Why doesn't my collision detection between two Area2D objects in Godot 4 work?

    Hi everyone I'd like to detect collisions between a circle and a floor. I have set them up as follows: The script runs fine (it's just a circle falling towards the floor), but nothing happens when the two objects collide. Does anyone know what I've done wrong?Thanks
  30. A

    Why is the work done double its expected value? (conveyer belt)

    The question was this: My calculations show that the answer should be equal to work done on crate to make it reach the same velocity which is equal to 216 J but the answer given is 432 J It is believed that extra energy is needed to overcome friction but friction is an internal force and...
  31. E

    Work done pushing a spring from the side

    My question is whether I've formed the integral for the work done correctly? It just seems a bit unwieldy to me... If I call the extension of the spring ## x ##, I can see that ## z = \frac l 2 + x ## and ## z^2 = \left( \frac {l} {2} \right)^2 + y^2 ##. Combining them gives: $$ x = \sqrt {y^2...
  32. C

    Work energy KE theorem for a book being lifted up in a gravitional field

    For this, From the work kinetic energy theorem, if we assume that the book and the earth is the system, and that the finial and inital speed of the system is zero, then is the work KE theorem there is no net work done on the system. However, clearly there is work done on the system is shown by...
  33. BWV

    Anyone able to get the MS Office CoPilot trial to work?

    There is a regedit floating around the internet that supposedly unlocks CoPilot, but did not work for me https://pureinfotech.com/enable-copilot-microsoft-word-preview/
  34. E

    Work done by a normal force (or rather, work NOT done)

    This question states that the normal force of the stairs on the woman does NO work. I do not understand how this can be. I would reason like this: The woman propels herself up the stairs using her legs. Her legs push down against the stairs, and the consequent normal force pushes upwards on her...
  35. nav888

    Work done by a force down a ramp

    The mass of the bike and person is 190kg Calculate the average accelerating force from X to Y, if the bike has a velocity of 30 at point Y. I am struggling with this question, I know that Fx = Work Done, but I also know that the only way to release GPE as KE is for gravity to do positive work on...
  36. H

    Automatic Window Opener - how does it work?

    Hi friends I'm working in a community center repair workshop once a week. One of our customers brought us an automatic window opener used for a greenhouse, and we were not able to find out how this contraption really works - but it does work, by using solar energy only. It consists of a hollow...
  37. Mohmmad Maaitah

    Work done by gravity and the minus sign

    Shouldn't work be minus when the man climbing up and force on him is down? shouldn't the power be also in minus? Can someone explain to me why is it positive please!
  38. nav888

    How does the calculation of work change for a rotating or non-rigid object?

    Here is the question, I am struggling with it as in all the past questions I have done it didnt matter if you worked out the work done by each force and then added it all together or if you added the forces together and then worked out the work done by the total force, but here the net force is...
  39. jedishrfu

    How LLMs work and other things

    https://www.wired.com/story/how-chatgpt-works-large-language-model/ The article mentions how Reddit and Stack want to monetize their content wrt LLM usage in their training sets. What do you think @Greg Bernhardt ?
  40. Argonaut

    Maximizing Range/Time in Air of an Airplane: Solving with Calculus

    Is my solution correct? (I only have answers to odd-numbered exercises.) Is it a good solution or have I overcomplicated things? (a) The forward force provided by the engine balances the air resistance force, so ##F_{engine}=F_{air} = \alpha v^2 + \beta /v{^2}##. Let ##W_{engine}## be the...
  41. S

    How do intra-oral scanners work?

    Hi. Needing a crown to cover a damaged molar, I’ve just returned from the first appointment with my dentist. The dentist used an intra-oral scanner to scan my teeth. This involved putting a ‘wand’ (about the size of a large electric toothbrush) against the insides and outsides of my teeth...
  42. V

    External forces required to move an electric dipole quasi-statically

    If the dipole is to be in equilibrium at all positions as it's moved so that it's always inclined at 60° to the horizontal, then the torque due to electric field needs to be balanced by torque due to external forces ##F_{ext}## as shown in above diagrams. But such external forces will not make...
  43. Lotto

    B What is meant by "upper limit of work done on Earth"?

    I think that the work is meant to be work done for instance in power stations. Or is it similar to work I do on a body when I lift it for example? But how can we then do that work on our Earth? I just need to understand the task, otherwise I want to solve it myself. The problem involves...
  44. S

    My Mistake? Understanding Friction Force & Work Done on Snowy & Icy Surfaces

    The answer is (D), but I don't understand why. Option (A) is wrong because the work done = 0. Then, I divide the motion into 3 parts: 1) motion on snowy surface Since the sledge is being pulled horizontally (let assume to the right), there will be tension force T to the right and friction...
  45. H

    I Which does more work: gravitation or electromagnetism?

    1: There is a universal gravitational force between two 1 kg iron balls, and the energy generated by their mutual attraction is so small that it is difficult to observe; there is also an attractive force between a 1 kg neodymium magnet and 1 kg of iron, but the energy generated by their...
  46. Altoid

    Why does the logic of negative acceleration not always indicate negative work?

    Knowing that negative work occurs when the force applied to an object opposes the direction of displacement, and that the direction of acceleration vector should align with the force vector, I assumed the correct answer was that the indication of negative work comes from negative acceleration...
  47. brochesspro

    I Does a person standing up on a swing in oscillatory motion do any work?

    Also, I wonder if a system can have work done to it due to its internal forces, as it is generally said that the work done due to internal forces is zero or at least I have learnt that(cannot trust my knowledge anymore, lol). I got this question in my mind because of a situation in another...
  48. amazofntheab

    Find the work from Newton's law of gravitation

    What I did was just sub in the numbers and convert km to m. So (6.67E-10)(1000)(5.98E24)/(1,000,000+6.37E6)^2 * (1,000,000+6.37E6) So it's just (6.67E-10)(1000)(5.98E24)/(1,000,000+6.37E6). I thought this was a straightforward problem, but it seems that it is not. What am I missing?
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