What is Work: Definition and 999 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:



{\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. 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...
  2. 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...
  3. physicsmaster123

    Work done by gravity on a car rolling down a hill

    I tried E =Fxcos0 but only ended up with 243kJ
  4. 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...
  5. 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...
  6. aliinuur

    I The gas work violates 2nd law of thermodynamics?

  7. 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...
  8. singularcell

    Heat Engine cyclic process

    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...
  9. 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
  10. 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...
  11. 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...
  12. 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...
  13. 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/
  14. 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...
  15. 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...
  16. 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...
  17. 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!
  18. nav888

    Work Done by a Couple

    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...
  19. 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 ?
  20. 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...
  21. 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...
  22. 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...
  23. 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...
  24. 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...
  25. 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...
  26. Altoid

    Energy with varying force

    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...
  27. brochesspro

    I Work and internal forces

    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...
  28. 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?
  29. shivajikobardan

    Comp Sci Call by address in C/C++, how does it work?

    I've asked my question in the figure below as picture speaks 1000 words. Code: #include<iostream> using namespace std; void change(int*,int*); int main() { int x,y; cout<<"Enter values of x and y"<<endl; cin>>x>>y; change(&x,&y); cout<<"In main()"<<endl...
  30. Argonaut

    Work-Energy Theorem Exercise

    My solution is different from the official solution and I don't understand what I did wrong. Here is my solution: The magnitude of the initial velocity is ##|v_0| = 12.0~\rm{m/s}##, so the vertical component of the initial velocity is ##v_{0-y} = (12.0 \sin{25^{\circ}})~\rm{m/s}##. Then I use...
  31. C

    Work done to compress gas

    For this problem, dose anybody please give me guidance how they got 74 K as the answer? Note that chat GPT dose not give the correct answer (it gives the temperature of the gas is 1500 K). Many Thanks!
  32. Wrichik Basu

    Any advice to make this Op-Amp temperature controller circuit work?

    As part of our UG curricula in Physics major, we have a practical in which we have to draw the calibration curve of an NTC ##10~\mathrm{\Omega}## thermistor, and then construct a circuit to maintain the temperature of a water bath. The calibration curve of our thermistor. The Prof. said that...
  33. doudou

    I Gravity does negative or positive work with cosmos redshift?

    Based on the fact of observed cosmological redshift, scientists have proposed different ideas to explain. One interesting question is whether gravity does negative or positive work now: According to universe expanding in Big Bang theory (Lemaitre, 1927), obviously gravity does overall negative...
  34. DomDominate

    B What exactly is spin? Does the standard model work without spin?

    I did some research online and found that "When certain elementary particles move through a magnetic field, they are deflected in a manner that suggests they have the properties of little magnets." To explain this phenomenon, physicists invented the concept of spin. So far so good. What I...
  35. L

    Rearrange formula and work out phase angle

    so far i think Ip = 10 f = 1000hz struggling with the phase angle
  36. C

    Work done on a gas when it is compressed quasi-statically

    For this derivation, I am not sure why the bit highlighted in orange is not positive since the displacement of the piston is downwards in the same direction as the force applied. Many thanks!
  37. H

    Finding the work done by a block

    We want to figure out how much work friction does on a block as it slides down an inclined plane with a rough surface. we find the force due to gravity that pulls the block down the ramp, that's found by M * g * sin(θ), The normal force on the block is given by M * g * cos(θ). The force of...
  38. E

    Inducing Voltage in a Transformer: How Does It Work?

    A changing current in a transformer primary produces a changing magnetic field, which induces a voltage in the secondary (correct?), but if no circuits are closed on the secondary, there's no current in the secondary (and therefore primary as well). So how is this voltage induced?
  39. Darmstadtium

    B Work Done during Free Fall

    For example, if a ball is from a certain height, the work done is 0 as there is no change in total energy the Ef =Ei. However, there is a constant force applied over a certain distance, suggesting work is being done. Which aspect am I forgetting/missing? Or is it that the definition of work done...
  40. S

    Empty Tank: Work Calculation w/ Origin at Apex of Cone

    I take the origin to be at the apex of the cone. Using the similarity of the triangle, where ##r## is radius of water and ##y## is height of water from the apex of cone: $$\frac{r}{y}=\frac{4}{10}$$ $$r=\frac{2}{5}y$$ The mass of water = ##\rho .V## = ##\rho . \pi r^2~\Delta y## = ##\rho . \pi...
  41. Jake357

    Work of the electric potential

    I tried to make the kinetic energy of the first electron equal to the electric potential work. mv^2/2=ke^2/d We have to solve for the minimum distance between them: d=2ke^2/mv^2=5.05*10^-10 m The force is: F=ke^2/d^2=9*10^-10 N, which is not correct.
  42. C

    Finding the work done by Spiderman

    For this problem, The answer is ##-4.70 kJ##. I am not sure what I am doing wrong. My working is ## W = mgr\cos\theta ## ## W = mgr\cos150 ## (since angle between ##\vec g## and ##\vec r## is 150 degrees) ## W = -mgr\frac {\sqrt{3}}{2} ## ## W = -mgr\frac {\sqrt{3}}{2} ## ## W =...
  43. LUFER

    A How does the dry process work using porous silicon?

    I'm having trouble finding in the literature specifically about the porous silicon process using the dry method instead of the more common wet method that is used. wet process Using porous silicon to promote wet thermal oxidation uses the process electrochemically will allow water molecules to...
  44. M

    I Adiabatic expansion work far exceeds isobaric of same volume, why?

    Using the adiabatic process formula, I've calculated the change in volume for a volume of gas with an initial pressure of 10 psig expanding to 0 psig. The initial volume is 100 cubic inches and the expanded volume is 144.9. This is a difference of 44.9. The total work done ends up being about...
  45. A

    Finding the final speed of a space probe using work and kinetic energy

    First I found work: W=(3.85x10^5)(2.45x10^8) W= 9.43x10^13 Then used that for difference of kinetic energy: 9.43x10^13 = (1/2) (4.55x10^4)v2^2 - (1/2)(4.55x10^4)(1.22x10^4)^2 9.43x10^13 = (22750)v2^2 - 3.386x10^12 9.43x10^13 + 3.386x10^12 = (22750)v2^2 9.77x10^13 = 22750v2^2 9.77x10^13/22750...
  46. A

    Net work and kinetic energy (pushing a wagon to accelerate it)

    I'm a little confused because my teacher used Bill's 500J of work for the kinetic energy equation and I don't understand why. I used the net work, so 300J, to find the speed and I'm not sure why that's wrong. Wouldn't friction make the wagon move slower than if there was no friction? So why...
  47. DioMiner

    Why does this not work? Projectile Motion problem for Dynamics Class

    TL;DR Summary: I want to mainly figure out where in the problem solving I went wrong. I understand the correct answer (since I looked it up), but to me, it does not make any sense. I am honestly stumped at this point. Online solutions say that my equation y = 0.5774x-0.003354x^2 should...
  48. T

    I cannot work out constants a and b --

    75 = (1.5 x 10^-3)a + (1.5 x 10^-3)b 105 = (3 x 10^-3)a + (3 x 10^-3)b
  49. S

    I Work done "against centrifugal force"

    Consider a merry-go-round (carousel) with a tube fixed radially on it. I use a pole to push a bowling ball slowly through the tube towards the center. (Slowly, so that the kinetic energy is negligible when the ball reaches the center. Also assume zero friction). What happens to the work that I...