Work Definition and 999 Threads

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.

View More On Wikipedia.org
Recent contents Top users
  1. Np14

    Energy Equation for a Roller Coaster on a Full Circular Loop

    Homework Statement What is the energy equation for a roller coaster already in motion from the ground with to the top of a full circular loop = point B in the image. My question is would the car still have kinetic energy at the top of the loop? Homework Equations Kinetic Energy Equation...
  2. J

    B Why the Fourier series doesn't work to solve any differential equation?

    I know this may sound as a stupid question but I would like to clarify this. An arbitrary function f can be expressed in the Fourier base of sines and cosines. My question is, Can this method be used to solve any differential equation? You plug into the unkown function the infinite series and...
  3. K

    Virtual work in Atwood's machine

    The first chapter in Goldstein's Classical Mechanics ends with 3 examples about how to apply Lagrange's eqs. to simple problems. The second example is about the Atwood's machine. The book says that the tension of the rope can be ignored, but I don't understand why. The two masses can move...
  4. T

    How much work is done when a satellite is launched into orbit?

    Homework Statement A Satellite is brought up into a geostationary orbit (altitude 35800km measured from the surface of the earth). Satellite weights 1000.0kg. How much work is required to bring satellite from a surface of the Earth to geostationary orbit? Homework Equations Newton's law of...
  5. jybe

    Thermodynamics: calculating work question

    1. Homework Statement What are the values of q, w, ΔU, ΔH for the following constant pressure process for a system containing 0.596 moles of CH3OH ? CH3OH(g, 123.0 ºC, 1.00 atm) ⟶ CH3OH(l, 30.0 ºC, 1.00 atm)Molar heat capacity for CH3OH(g), Cp,m = 44.1 J K−1 mol−1 Molar heat capacity for...
  6. I

    How long does it take for gravitational effects to work?

    Imagine a ball being tossed into 'the air'. At its peak, the ball has a velocity of 0(m/s), but how long does it actually have this velocity for? --> Neglecting the effects of air-resistance. Obviously the ball undergoes constant 'g' the whole time, but the answer to my question doesn't relate...
  7. D

    Chemistry Volunteer/unpaid work to build skills

    I got a chemistry degree a few years ago bit I didn't use it to get a job since I've been doing other things. I love working in the lab and would really love to build up my skills but I don't see myself getting a paid chemistry job any time soon so looking for another way to gain lab experience...
  8. Burhan Uddin

    Calculating the work done using a line integral

    Homework Statement a) A point charge + q is placed at the origin. By explicitly calculating the relevant line integral, determine how much external work must be done to bring another point charge + q from infinity to the point r2= aŷ ? Consider the difference between external work and work...
  9. S

    I How does magnetism work in QM?

    Electrons' spin state is responsible for magnetism inside a magnet. Two magnets interact at a distance, but what about the space between and around the two magnetic objects? In CM there are field lines and vector fields, but what is actually happening at the QM level?
  10. L

    How do we calculate kinetic and potential energy in physics?

    Hello:) Ok, I am in my thermos class and I ran into a question about work and energy. I figured out the correct answer based off of the formula given. But what MY question is, goes back to physics 1. How are work and Ke related? IE, work is F*d and F is mg. But in Ke, I do not see the g. How...
  11. C

    Calculating the final speed w/ work & friction

    The problem is asking me to find the final speed of a 1100 kg car traveling at 24 m/s through 18m of mud, where the resistive force on the car is 17000 N. I don't actually know how to go about doing this, so any pointers in the right direction would be super helpful.
  12. N

    Exploring Thermodynamic Work: PV, Mechanical, and Non-Mechanical

    In thermodynamics, what is the relationship between the terms, "pressure–volume work", "mechanical work", "non-mechanical work", "∫pdV", and "-∫Vdp"?
  13. jybe

    How Do You Calculate Work When Compressing Gas?

    Homework Statement What is w when a gas is compressed from 42.1 L to 25.1 L using a constant external pressure of 739 Torr? Remember to include a "+" or "−" sign as appropriate. Homework Equations W = -P(dV) The Attempt at a Solution Pressure = (739 Torr / 760 Torr)*(101.325 kPa) W =...
  14. Ben Harris

    Work done on a meteor approaching the Earth -- Is it +ve or -ve?

    Hi all, i am trying to figure out if work done by gravity is positive or negative on an approaching meteor, I have used W(1->2) = integral (1->2) F(gravity) dot dr. and got a result of (GMem/r2) - (GMem/r1). Were G is gravity, Me is Earth mass, m is meteor mass and r1, r2 are initial and...
  15. MermaidWonders

    MHB Help with Lab Work: Acids and Bases Safety

    Which of the following will burn your skin if you get it on you? a. concentrated sulfuric acid b. concentrated nitric acid c. concentrated potassium hydroxide d. concentrated hydrochloric acidMy first instinct was that all of them would since they are either concentrated acids or bases. I then...
  16. R

    Oil-Water-Salt - What's the force at work here?

    Hi, This is something I observed in the kitchen when I was cooking something. I had put some water in a vessel, to which, I added couple of spoons of oil. The oil formed large droplets on water surface. I then sprinkled normal table salt crystals on to the water surface and they sank to the...
  17. L

    Total Work versus External Work

    Is there an important difference between total work and external work? My knowledge would be that total work a.k.a. net work on a system would be equal to the change in kinetic energy of that system and equal to the line integral of the net force on the system dotted with the differential...
  18. P

    Thermodynamics Problem: Calculate the heat input for this work output

    Homework Statement An inventor claims to have developed a device with the following properties: net work output per cycle = 20,000 J heat output per cycle = 50,000 J high temperature = 450 C low temperature = 160 C Calculate the heat input per cycle. Homework Equations ΔETH = W + Q efficiency...
  19. S

    Gravity equation -- check my work please?

    Homework Statement My answer seems really off and wondering if someone could just look at it before I submit answer? Two 65 kg astronauts leave Earth in a spacecraft , sitting 2.4 m apart How far are they from the center of the Earth when the gravitational force between them is as strong as...
  20. J

    Understanding Work Against Friction in Physics

    When we say the work done against friction, what do we mean by that? This concept is really worrying me.Thanks in advance!
  21. A

    Engineering Have trouble finding work (PhD in Materials Science & Engineering)

    I am about to graduate with a doctorate in a Materials Science & Engineer degree. I have the following experience: - Mechanical testing such as indentation and bend testing - X-ray/neutron diffraction characterization (in/ex situ)...
  22. Ben2

    Does Simplex work for all standard-max problems?

    Mentor note: Fixed the LaTeX 1. Homework Statement Maximize ##5x_1 + 7x_2 + 3x_3## subject to ##x_1 + x_2 + x_3 \le 28, x_2 \le2 x_1## and ##x_1 \le x_3##. Homework Equations ##x_1\ge 0, x_2\ge 0, x_3\ge 0##. The Attempt at a Solution Problem is workable by graphic methods, but the writer has...
  23. M

    Engineering What non-nuclear fields can a nuclear engineer work in?

    Hi, I am almost done with my 5 years of a bachelor of nuclear engineering, the main field I am working on is thermal-hydraulic but I am flexible with changing my whole path. for example, I am in between data science and CFD analysis. What kind of jobs do I qualify for?
  24. B

    Work done on the system through a piston?

    I am stuck on like the first page of thermal physics. It seems like the signs of the work done on the system are opposite when the volume is expanded and compressed. But when I imagine myself pushing or pulling the piston, I get confused from W = \textbf{F}\cdot \textbf{d} This work will be...
  25. M

    Physics Is Devoting My Soul to Science Worth It?

    I am concerned about devoting my soul into science(Physics, Math, and Chemistry particularly). I imagine the supposed efforts that I will put in my future works will not be seen by humanity as the way I would like(as an example in history, many scientists who dedicated their lives ended not...
  26. F

    Is Mechanical Energy Conserved for Non-Conservative Forces?

    Hello, A generic force ##F##, which may be conservative or not, performs mechanical work which is always equal to $$W=\Delta KE=KE_{final}-KE{initial}$$ i.e. produce a change in the object's kinetic energy ##KE##. Work is essentially a way to inject or subtract kinetic energy from a system. If...
  27. mayank pathak

    Maximum Work Theorem : Herbert Callen

    Hi, I have been studying thermodynamics from Herbert Callen's "Thermodynamics : an introduction to the physical theories of equilibrium thermostatics and irreversible thermodynamics" In Chapter 4, Section 4.4, he writes : " all processes occurring between a given initial and a given final state...
  28. S

    Determining Work Done by a Person on a Luggage

    I'm trying to determine the work done by a person as they pull a luggage up a ramp. The ramp has a height of 5 m and the distance the person walks up is 20 m. The weight of the bag is also 10 kg. I am trying to compare the work done by pulling the luggage up a ramp to carrying an equally heavy...
  29. T

    What Is the Average Power of Bullets Bouncing Off Superman?

    Homework Statement When bullets are shot on Superman, they bounce off of his chest. 100 Bullets will be shot on his chest per minute, each with a mass of 9g and v= 1000m/s. Assume that the bullets will bounce off elastically back in x-direction. a) What is the average power of all of the...
  30. WeiShan Ng

    [Fluid Mechanics] Negative sign on the viscous work term

    Homework Statement I am revising on the derivation of the differential equation of energy (White's Fluid Mechanics 7th ed) and I'm having trouble understanding the sign convention used in the viscous work term. The textbook first define an elemental control volume and list out the inlet...
  31. A

    Work Adiabat 1rst Law Calc VS Adiabat Calc

    Hello there, I have been working on the efficiency of engine problems and have some trouble with this one. My question is very specific. If you scroll down to the line encircled in red, you see that the Work they calculated there was 2662 Joules based on the formula derived for the work of an...
  32. I

    Does greater acceleration result in more work done?

    Work W done by moving the object with force F for distance s is W = Fs. When I move the same object the same distance but with twice the acceleration, does the work done gets also doubled? By F=ma, doubling the acceleration yields m*2*a = 2F -> 2Fs = 2W. I've mostly read, that if I want to...
  33. R

    Work Done on Charges by a Capacitor and an Inductor

    Homework Statement https://imgur.com/vQRoMjZ Homework EquationsThe Attempt at a Solution I believe that the inductor does negative work on the charges via the electric field (by way of induced EMF). I am unsure about how the capacitor would be doing positive work, though. Can anyone help steer...
  34. T

    Kinetic energy & Conservation of energy

    Homework Statement You are driving with your car (of total mass: 1.2tonnes) with a speed of v=50km/h, until you see an obstacle. a) What is the kinetic energy of the car? b) When you start to brake, there is still 15m until the obstacle. What must be the size of the friction coefficient (µ)...
  35. I

    Maxwell's Law of Induction - How Does it Work?

    So, I was studying Maxwell's equations and I don't really understand the last one - Ampere's Law (with Maxwell's extra term added in). The bit I'm not able to understand is the term Maxwell added. How exactly does a changing electric field through a closed loop induce a magnetic field along that...
  36. A

    Why is the Work Zero on a Frictionless Surface?

    Homework Statement Is the work zero here because its a frictionless surface? If, so why? If not then what's the reason and why? Homework EquationsThe Attempt at a Solution I was originally thinking 1/2mv^2 .. but KE is zero right, but having it be mgh didn't make sense..
  37. A

    Physics — Net work on a box being pulled…

    Homework Statement How to calculate the net work Homework Equations A 5 kg box is pulled with a force F = 100 N for 5 m long inclined plane. The height of the inclined plane is 4 m and angle of inclination is 53^ a) What is a work done by force F? b) What is the work done normal force N? c)...
  38. trungnguyen89

    Does This Engine Function Properly?

    Does this engine work?
  39. S

    Homework help: Work and Energy, Free fall

    Homework Statement A 200 kg object moves at 10 m/s at 20m (vertically). It falls to a height of 5 m. Find the new speed. Homework Equations vf²=vi²+2ad The Attempt at a Solution vf²=(10m/s)²+2(9.8m/s²)(15m) vf=19.8m/s To find the distance for the new speed I did 20-5, but I'm not sure it's...
  40. S

    Homework help: Work and Energy: Spring

    Homework Statement A .5 kg loaded toy (spring k=8000 n/m) loaded toy is compressed .05 m and fired on a flat surface a) Find the new speed it was released with b) If it approaches a hill find the maximum height it can climbHomework Equations KE=1/2kx² KE=1/2mv² PE=1/2kx^2 The Attempt at a...
  41. D

    How do wet/dry vacuum cleaners work? What is the physics behind them?

    I have a problem designing and understanding Wet and Dry vacuum cleaners. I understand some of the basics behind pressure however things I need to know is: what pressure/ velocity is needed to suck up water? how to calculate the pressure and velocity generated by the fan? (some examples of...
  42. T

    Finding the Work of a spring and friction with a changing angle

    Homework Statement We shot a projectile with mass ##m## and velocity ##v_0## with angle ##\phi## it collide with a box with mass ##M## at the maximum height of its path. Then, they both start to move with another speed. (We define ##t=0## at this time) (Completely Inelastic Collision). The box...
  43. B

    Question on the work done while charging up a capacitor.

    So the work done when charging up a capacitor is ##dW=VdQ## However, when we add a charge ##dQ## to the capacitor, ##V## also changes accordingly, so I was wondering why the work done wasn't written as ##dW=VdQ+QdV## (one that also takes into account t he change in ##V##). Thanks in advance.
  44. T

    Question about the Work-Kinetic Energy Theorem - Pulling a cart

    Homework Statement Question from Fundamentals of Physics (Halliday, Resnick, Walker) This figure below shows a cord attached to a cart that can slide along a frictionless horizontal rail aligned along an x axis. The left end of the cord is pulled over a pulley, of negligible mass and friction...
  45. sophiecentaur

    The common or garden Dividing Head - how does it work?

    I have looked all over the net and can only find descriptions of how to use a dividing head, followed by countless numerical examples. There must be someone on PF who can give a short algebraic description of the way they work. Machinists as a whole, don't seem to want to present the topic in a...
  46. D

    Understanding the Work-Energy Theorem

    Are the following definitions correct? Work done as energy transferred The energy transferred when the forces between two objects interact Work done by a force Work done = force x distance moved in the direction of force applied (W=F*Δs) Work done by a gas Work done = pressure x change...
  47. C

    Definition of work done by torque

    I' m trying to derive the work done by a torque from W = ∫ F ⋅ ds and I' ve looked up the internet, it said: W = ∫ F ⋅ ds ( since ds = dθ × r ) ---------------------------------------- ( Line 1 ) it can be written as W = ∫ F ⋅ dθ x r this is a vector triple product , thus can also...
  48. kolleamm

    Work done by a force on a spring

    Homework Statement The unstretched length of a spring with 'k' = 250 N/m is 20 cm. A force 'F' is applied to stretch it to a length of 24 cm. How much work was done by 'F'? Answer : 0.2 Nm Homework Equations F = k * delta x Work = F * delta x The Attempt at a Solution [/B] change in spring...
  49. J

    Speed or turning point using energy

    Homework Statement Please look at the attached screenshot. This problem is really confusing for me and I can't seem to make much sense out of it. Homework Equations Ei = Ef The Attempt at a Solution As you can see, I did get (a). (The other checkmarks, I guessed — there were only two...
  50. T

    A question about optics: Why does a pinhole aperture work like my eyeglasses?

    i wear glasses to correct my out of focus vision. Without glasses everything is slightly out of focus. Quite by accident I looked through a tiny pinhole about the size of a pinprick without my glasses using one eye. To my amazement everything was perfectly sharply in focus. The same with...
Back
Top