What is Circular: Definition and 1000 Discussions

A circular economy (also referred to as "circularity") is an economic system aimed at eliminating waste and the continual use of resources. Circular systems employ reuse, sharing, repair, refurbishment, remanufacturing and recycling to create a closed-loop system, minimising the use of resource inputs and the creation of waste, pollution and carbon emissions. The circular economy aims to keep products, equipment and infrastructure in use for longer, thus improving the productivity of these resources. Waste materials and energy should become input for other processes through waste valorization: either as a component or recovered resource for another industrial process or as regenerative resources for nature (e.g., compost). This regenerative approach is in contrast to the traditional linear economy, which has a "take, make, dispose" model of production.In recent years, concepts based on (re-)cycling resources are increasingly gaining importance. The most prominent among these concepts might be the circular economy, with its comprehensive support by China and the European Union. There is also a broad range of similar concepts or schools of thought, including cradle-to-cradle laws of ecology, looped and performance economy, regenerative design, industrial ecology, biomimicry, and the blue economy. These concepts seem intuitively to be more sustainable than the current linear economic system. The reduction of resource inputs into and waste and emission leakage out of the system reduces resource depletion and environmental pollution. However, these simple assumptions are not sufficient to deal with the involved systemic complexity and disregards potential trade-offs. For example, the social dimension of sustainability seems to be only marginally addressed in many publications on the Circular Economy, and some cases require different or additional strategies, such as purchasing new, more energy-efficient equipment.

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  1. vibha_ganji

    Another Doubt From Halliday Resnick Krane -- Puck on a string in circular motion

    Hello! This is a problem from Halliday Resnick Krane (Chapter 4: Problem #15). “A puck is moving in a circle of radius r0 with a constant speed v0 on a level frictionless table. A string is attached to the puck, which holds it in the circle; the string passes through a frictionless hole and is...
  2. G

    B Resultant force in vertical circular motion

    Suppose we have a vertical circular motion with gravity according to the image below. In the leftmost and rightmost positions the resultant force is pointing diagonally down. Isn't the resultant force supposed to be pointing at the center at all times in a circular motion? What am I getting...
  3. H

    What is the meaning of work done for non-uniform circular motion?

    This is my solution ,and I just use the definition .But I still feel unclear about the concept of non-conservative force.$$ W = F x = 30N (\frac{1}{2}\pi r ) = 56.2 J $$ $$ E_{system} = \Delta K + \Delta U = W $$ $$ (K_{f}- K(i))+(U(f)-U(i)) = W $$ $$ (\frac{1}{2} *m{V_{f}}^2...
  4. Z

    Electric field created by two charged circular arcs?

    The strategy will be to figure out what ##dq##, ##\hat{r}_{dq,p}##, and ##r_{dq,p}## are, plug them into the expression for ##d\vec{E}_{p_r}##, then integrate over ##d\vec{E}_{p_r}## to obtain ##\vec{E}_{p_r}##, the electric field at ##P## due to the arc on the right. Then I will repeat the...
  5. Z

    How to calculate differential work done by a force in circular motion?

    My question is, is this correct, and if so, why the minus sign?
  6. P

    Equilibrium circular ring of uniform charge with point charge

    This is an offshoot of @Angela G 's thread. I don't want to hijack her thread so I decided to create a new one. Original thread https://www.physicsforums.com/threads/unstable-or-stable-electrostatic-equilibrium.1007881/ @kuruman @PeroK @bob012345 If you have the time I'd appreciate your input...
  7. gromit

    Using Lagrangian to show a particle has a circular orbit

    Hi :) This is a problem from David Tong's Classical Dynamics course, found here: http://www.damtp.cam.ac.uk/user/tong/dynamics.html. In particular it is problem 6ii in the first problem sheet. Firstly we can see the lagrangian is ##L = \frac{1}{2}m(\dot{r}^2+r^2\dot{\theta}^2+\dot{z}^2) -...
  8. Father_Ing

    Torque formula derivation for a particle moving in circular

    Consider that the particle is moving in circular with tangential velocity v, and (0,0)is its origin. I wonder why dr/dt is equal to tangential velocity instead of radial velocity (since dr/dt means how much change in radial distance in a really short duration of time)
  9. Shreya

    Tangential & Normal acceleration in Circular Motion

  10. bob012345

    I Divergence of the Electric field of a charged circular ring

    In a previous thread* the field in a charged ring was discussed and it was shown to be not zero except at the center. In *post #45 a video is referenced that says the field diverges as one gets close to the ring and it was argued that at very close distances the field looks like an infinite line...
  11. T

    Circular motion of a mass on a string on an inclined plane

    (I drew motion in the opposite direction so the object would rotate trigonometrically but it should be the same thing) I have just finished the Kinetic Energy and Work chapter in my course and this is the last problem from the problem set. I have not worked many problems with the Work-Kinetic...
  12. V

    Electric field at a point within a charged circular ring

    I have broken the ring into a top arc and a bottom arc. First, let's assume an imaginary charge of +1 C is placed at point P. We will determine the force on this unit charge from top and bottom arcs. The charges in the top arc will result in electric fields that will all cancel each other...
  13. Rubberduck2005

    Bead sliding on a Vertical Circular Loop versus in Free Fall

    I can evaluate the first beads motion easily A to B is -2Rj considering the point B as y=0 the motion of the bead will be -gt^2/2+2R=0 which implies t=2√(R/G) , this is ok but what I am struggling with is A to C I can see that the angle between the beads weight and it's negative normal force...
  14. brotherbobby

    Prove an equation involving inverse circular functions

    (I must confess that, in spite of working through the chapter on inverse circular functions, I could barely proceed with this problem. Note what it asks to prove : ##x\sqrt{1-x^2}+\ldots## and how much is that at odds with the formula (1 above) of adding two ##sin^{-1}##'s, where you have...
  15. grotiare

    Engineering Question about max stress on circular cross section with two moments

    I couldn't fit in the title, but this is with a hollow circular cross section So currently I am trying to figure what occurs when two, perpendicular bending moments are applied to a hollow circular cross section (one about the z axis, and the other about y). I know that if I was dealing with a...
  16. S

    Tension of string acting on stone moving in horizontal circular motion

    Is it possible for the stone to move in horizontal circular motion just like in the picture? I try to draw the free body diagram of the stone and there are two forces acting on the stone, its weight (directed downwards) and the tension of the string (directed to the left). The tension will...
  17. C

    I Non-uniform Circular Motion & Acceleration

    I would really appreciate some help with this problem regarding non-uniform circular motion, in which a body is accelerating as it follows a circular path. If we take Example 1, a body starts at Point A with an angular speed of 180°/s. The body accelerates to Point B and reaches it some time...
  18. V

    Would particle P be under non-unform circular motion?

    At t= 0, we can see that the particle P has a radial acceleration of ##-2\hat j## and a tangential acceleration of ##2 \hat i##. The radial acceleration will tend to move it in a circle of a certain radius, whereas the tangential acceleration will tend to displace it parallel to x- axis...
  19. SAMAHIR

    Analytical question: circular rotation

    Can a point P on the smaller wheel trace a straight line path inside the circular road (like the walls of a well)
  20. C

    I Determining Future Position of Uniform Circular Motion

    Hello, Apologies if this is in the wrong section, it's related to circles so I figured Geometry was the best place. I found a very good example online that explains how to determine a future position of an object undergoing uniform circular motion: (Note that they made a mistake by writing...
  21. F

    Tension in rope for non-uniform circular motion with air resistance

    I'm trying to solve this problem using an rtz coordinate system, and Newtons second law. I know that mar = (m(v)2)/r. I'm failing to understand how mg and the drag force affects the solution and how I would set it up. I know if it was at the bottom of the circle that mg would be added to the...
  22. Erik Ayer

    I Question on circular polarization and the quantum eraser

    Looking at the wikipedia page for the (original) quantum eraser (https://en.wikipedia.org/wiki/Quantum_eraser_experiment), quarter-wave plates in front of the slits change photons from being linearly polarized to being circularly polarized. I think this is the case when there is no polarizer in...
  23. RoboRaptor

    A Car on a Banked Curve Moving in Uniform Circular Motion

    First I figured out the normal force being exerted on the car using the equation above. Cos(40°)*(1050*9.8) = 7883N Next, I tried to find out the horizontal component of the normal force by doing: Cos(50) * 7883 = 5067N I figured out the angle by using certain geometrical properties. Next, I...
  24. John Mohr

    Constant Circular Motion Not Really Constant

    I was pondering my practice of talking about circular motion in the horizontal direction and the vertical direction. But I'd often would see in books, notes, and the internet that we assume constant velocity for the vertical case. However, when one thinks about the forces at different points in...
  25. L

    Circular Motion Questions (energies, forces, angular velocities, etc.)

    Question 1: I believe that the ratio would be b. 8:1 because by combining the formula for kinetic energy and momentum the expression Ek=p^2/2m can be obtained. Thus, for a body of mass 2kg with twice the momentum: Ek=2^2/2*2=1 For a body of mass 4kg with half the momentum: Ek=1^2/2*4=1/8...
  26. V

    Circular motion of a particle around a track -- what provides the centripital acceleration?

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  27. Traced

    Determine the speed and tension of keys swinging in a circular path

    a)Determine the slowest speed that the keys can swing and still maintain a circular path. Fnet = Fg + Ft Fc = Fg + Ft When Ft = 0, Fc = Fg So, Fc = mv^2 / r and Fg = mg mv^2/r = mg v = √gr v = √9.81 * 0.25 v = 1.56 m/s Therefore, the slowest speed that the keys can swing and still maintain...
  28. Steven Ellet

    Can a horseshoe magnet without separated poles still function as a magnet?

    If you take a horseshoe magnet and fuse the north and South Poles together (without destroying the magnetic field) would you have a “pole-less” magnet? And if so, what special properties would it have(other than other magnets)?
  29. E

    Kinematics: Analyzing circular motion of a particle

    Help please
  30. Kaguro

    Finding directions of fast axis to cause circular polarisation

    The only thing I can think of is that to create a circularly polarized wave the axes of the quarter wave plate will have to be at 45 degrees to the E vector. Only then it can have both components on the slow and fast axis equal. Then the slow axis will cause delay and the resulting vector will...
  31. Kaguro

    Circular polarizer followed by a linear analyser

    I think that the intensity of output of circularly polarised light falling on an analyser should not depend upon the axis of analyser. Because it is circularly polarized. It keeps rotating. So, the output should be linearly polarised. The amplitude of E field in the direction of analyser is a...
  32. rxh140630

    Optimization problem - right circular cylinder inscribed in cone

    Please I do not want the answer, I just want understanding as to why my logic is faulty. Included as an attachment is how I picture the problem. My logic: Take the volume of the cone, subtract it by the volume of the cylinder. Take the derivative. from here I can find the point that the cone...
  33. sahilmm15

    B A problem of circular permutation

    I have understood everything till 2nd paragraph. But after that everything was above my head. Can you explain me the concept
  34. U

    Circular antenna array formula

    At page 20 of this pdf the two formulas that characterize the behavior of a linear and a circular antenna array are compared. The reason why I write this post is: I don't understand why the second formula is true. Below I show why I am not convinced. In general, given a configuration of sources...
  35. yucheng

    Contradictory Proof of Supremum of E: Is it Circular?

    N.B. I have inserted the proof here as reference. See the bolded text. My question is, isn't the reasoning "##x^{2}+5 \varepsilon<2,## thus ##(x+\varepsilon)^{2}<2 .## " circular? If we can already find an ##0<\varepsilon<1## such that ##x^{2}+5 \varepsilon<2,## Can't one also claim that " we...
  36. L

    How does a wave with circular polarization behave?

    does an em wave with circular polarization behave like a coil, i.e. do perpendicular electromagnetic fields join internally? I am very confused on this subject
  37. cle102

    Uniform Circular Motion on a racetrack

    Not sure what I'm doing here. Not sure how to continue? Please help. Thank you in advance!
  38. cle102

    Uniform Circular Motion: banked race track circular path

    Basically, I need help to continue on this question. This is what I have now: Angle of the race track (angle of the grey part): tan(18/(169-108)) = 0.30396 Not sure how to continue?? What am I supposed to do and find next? Thank you in advance! :smile::blushing::oldbiggrin:
  39. greg_rack

    Circular trajectory traveled by a charged particle in a magnetic field

    The Lorentz's force acting on a charged particle perpendicularly "hitting" a magnetic field will be directed upwards, and generally directed towards the center of the circumference traveled by this particle, and so will cause a centripetal acceleration to keep it in a circular motion. By...
  40. Ranku

    Circular and linear freefall

    Does circular freefall of an object involve cancellation of gravitational and inertial forces, as it does in linear freefall?
  41. WhiteWolf98

    Calculating Discharge Rate of Fluid in Circular Area

    This is actually right at the start of another derivation, but I can't understand how the author gets the formula for ##q##. So the discharge per unit thickness is the circumference of the circle, multiplied by the velocity at that point (at ##r##)? I thought the formula for flow rate was...
  42. I

    Learning Data Structures in Java: Circular Queue

    Summary:: I have recently started with data structures in java and I tried doing this Program .But I have few confusions. 1.How do I write the main() of the program? 2.What are we supposed to do with the value returned by function pop()? If anyone could point out if there are any errors and...
  43. Athenian

    2D Steady-state Temperature in a Circular Plate - Bessel Function

    I learned about Bessel functions and steady-state temperature distributions in the past. Recently, I was searching online for some example problems on the topic and found the "original question" along with the solution online as a PDF file. While I am unsure will it be appropriate for me to...
  44. karush

    MHB Apc.2.8.1 ap vertical circular cylinder related rates

    $\tiny{2.8.1}$ The vertical circular cylinder has radius r ft and height h ft. If the height and radius both increase at the constant rate of 2 ft/sec, Then what is the rate at which the lateral surface area increases? \een $\begin{array}{ll} a&4\pi r\\ b&2\pi(r+h)\\ c&4\pi(r+h)\\ d&4\pi rh\\...
  45. M

    What is Kepler's Formula and How is it Used in Circular Motion and Gravitation?

    Using Kepler's Formula, I tried to solve for the answer but was told that it's incorrect.
  46. B

    I Muon Time Dilation in Accelerating Frames

    Hi In the book, "Why does E= mc2" by Cox and Forshaw, while discussing time dilation, the example of a muon is given. The authors explain that muons when circulated in the 14 m diameter AGS facility at Brookhaven at 99.94% of the speed of light, its lifetime is increased from the value of 2.2...
  47. AN630078

    Potential Energy and raising a satellite from Earth into a Circular Orbit

    a. V=-GM/r V=-6.67*10^-11*6.0 x 10^24/6.4 x 10^6 V grav = -62531250 ~ -62.5M Jkg^-1 b. To find the gravitational potential 200 km above the surface of the Earth; r=6.4 x 10^6 +2*10^5 m=6.6*10^6 V grav=-6.67*10^-11*6.0 x 10^24/6.6*10^6 V grav= -60636363 ~ -60.6 M Jkg^-1 Can I check that it is...
  48. Like Tony Stark

    Tension and reaction force in circular motion

    Hi I'm having trouble to understand the centripetal force in a rotating rod with a mass in its end. When ##90°<\theta<270°##, the centripetal acceleration is produced by the tension, which counteracts the radial component of the weight. But what happens when ##\theta<90°## or ##\theta>270°##...
  49. V

    I Object in or out of a circular field of view? (celestial coordinate system)

    In celestial coordinate system (right ascension/declination), how to check if an object with position RA and dec is within a given circular field of view of radius R (in arcminutes) and centred at (0,0)? R is small in this case so I assumed that I could compute the distance d of the object from...
  50. P

    I Stability of circular orbits in an arbitrary central force field

    In this chapter, the stability of an object orbiting in a circular orbit of radius r_c in an arbitrary force field f is considered. The author arrives at the equation of a harmonic oscillator, for small deviations x from the circular orbit: \ddot{x} + \left[-3\frac{f(r_c)}{r_c} -...
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