What is Sphere: Definition and 1000 Discussions

A sphere (from Greek σφαῖρα—sphaira, "globe, ball") is a geometrical object in three-dimensional space that is the surface of a ball (viz., analogous to the circular objects in two dimensions, where a "circle" circumscribes its "disk").
Like a circle in a two-dimensional space, a sphere is defined mathematically as the set of points that are all at the same distance r from a given point in a three-dimensional space. This distance r is the radius of the ball, which is made up from all points with a distance less than (or, for a closed ball, less than or equal to) r from the given point, which is the center of the mathematical ball. These are also referred to as the radius and center of the sphere, respectively. The longest straight line segment through the ball, connecting two points of the sphere, passes through the center and its length is thus twice the radius; it is a diameter of both the sphere and its ball.
While outside mathematics the terms "sphere" and "ball" are sometimes used interchangeably, in mathematics the above distinction is made between a sphere, which is a two-dimensional closed surface embedded in a three-dimensional Euclidean space, and a ball, which is a three-dimensional shape that includes the sphere and everything inside the sphere (a closed ball), or, more often, just the points inside, but not on the sphere (an open ball). The distinction between ball and sphere has not always been maintained and especially older mathematical references talk about a sphere as a solid. This is analogous to the situation in the plane, where the terms "circle" and "disk" can also be confounded.

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  1. T

    Work done to construct Dielectric Sphere with Offset Hollow Cavity?

    My thinking would be to do a work integral Work = integral dWork = integral delta V dq = integral delta V 4(pi r^2) dr The problem is, is this possible with a single integral? Due to the offset cavity, the electric field E will not be constant at a given r.
  2. J

    The electric potential inside a conducting sphere with charge Q

    If there is no field inside the conductor, how can there be electric potential? I think of potential very similar to gravity, as how much energy would be required to move a particle of mass/charge against the gravitational/electric field. If there is no field at all, how would there still be...
  3. Vanadium 50

    I Spherical trig - sphere radius from 6 lengths

    Four points lie on the surface of a sphere. Given the six distances between the points, calculate the radius of the sphere. This is (allegedly) an advanced high school level problem. However, it is a remembered problem, so it is possibly misremembered (i.e. there might have been some “bice...
  4. brotherbobby

    Depth of a basketball floating on water

    Attempt : (Turns out, there is more mathematics in this problem than physics. The crucial part involves the use of vector calculus where one needs to find the volume of a region bounded at the top by a portion of a sphere. That is where am stuck.) The mass of water displaced by the ball...
  5. T

    Charge on a grounded conducting sphere in a uniform electric field, after ungrounding and movement

    Question 1: The sphere is at the electric potential of the top plate. As the sphere is small with respect to the capacitor, one can consider the bottom plate to be at infinity and therefore we can use the capacitance formula as C = 4 ∏ε0 R. The charge Q is therefore Q = C (V -0) = C V...
  6. lola9

    A sphere suspended from a cord -- Find the tension

    I don't understand where F comes from because in the problem there is only the tension of the cord. And I have another question the forces along y-axis always be equal to zero? And why T cos q - m g = 0 equal zero? if it is along the X-axis
  7. SiRiVeon

    Conservation of energy problem: Ball rolling down inclined plane and then through a loop-the-loop

    Hello, this question may seem weird but I really need help on this. To bring the formula for the height h of the triangle above, I have to create a relation between potential and kinetic energies of the black ball with mass m (I can't find any other methods than this). For a sphere falling...
  8. C

    B Question about volume of a sphere

    Hello everyone, I was trying to find volume of a sphere by doing some calculus, the area of a circle is ##{\pi}r^2## So I thought I would calculate the volume of one hemisphere and then multiply by two, but I got a different result than the standard formula, the standard formula is ##\frac 4 3...
  9. L

    Dipole Moment of a Hollow Sphere, simplify calculation

    is there an easier way to calculate the dipole moment? I described ## \vec r## in spherical coordinates. I thought at first that due to the symmetry I can assume that dipole-moment only points in the ##z##-direction, but the charge distribution is inhomogeneous, so I made the following...
  10. Theexploer

    A sphere held steady on a slope by a rope

    The sum of the forces should be 0. Sin A'C'B' = px/b px = mg . sin alpha P should be px = - m.g. sin alpha and py = m.g.cos alpha Finally i fund as result F = -0.8 and R = -1.23 but for the second question i didn't fund the radius of the circle.
  11. G

    Calculate the area intersected by a sphere and a rectangular prism

    Think of a 3D rectilinear grid made of these rectangular cells, some of the cells will intersect with the sphere. I am trying to compute each intersecting area and the total sum. Ideally the total sum of the intersecting area should be close to ##4 \pi r^2##. I have not found any literature...
  12. L

    Calculate the magnetic moment of a rotating sphere

    Ich wäre Ihnen sehr dankbar, wenn Sie sich meine Lösung der folgenden Übung ansehen: A sphere with radius ##R ## is spatially homogeneously loaded and rotates with constant angular velocity ##\vec{ \omega}## around the ##z ## axis running through the center of the sphere. Calculate the...
  13. Y

    I Force applied on sphere by turbulent flow

    Hello everybody, I am thinking of the following problem: A sphere a radius r is in a much larger container of radius R. In this container, a fluid continuously flows with turbulent conditions from bottom to top. I would like to approximate the force pushing the sphere up. Some calculations I...
  14. A

    B Can I use this method to charge a metal sphere?

    Consider a metal sphere connected to one end of the battery and the other end of the battery to be connected to the ground. Does the metal sphere become electrically charged with this method?
  15. Q

    Motion of Sphere Rolling Down Rotating Cone

    I am trying to understand the motion of the sphere in the image above, and I am a bit confused about the motion. How does the ball move down the cone? Will the rotation of the cone cause the ball to rotate with it, and which direction would the static friction be in? What does the path the ball...
  16. P

    A How much thickness for sphere to withstand atmospheric pressure?

    Imagine a hollow sphere made of a material with high elasticity constant(e.g. steel). How much thickness should it have to prevent it from crushing when the air inside is pumped out? Is it valid to use Lame solution to quantify the answer? What about Finite Element Analysis?
  17. P

    Charge density in sphere that makes constant radial E-field inside

    I'm having trouble understanding how a charge distribution in a sphere can make this happen. My instinct is that the fact that it's radially directed is a big hint of something, but I don't know what that hint might be alluding to. If the net E-field is constant inside the sphere and is always...
  18. MatinSAR

    Change in volume of sphere with change in temperature

    I am sure that the radius of the two spheres changes equally. But in answer of the question it said that their change in volume is the same. Is it correct?! Link of website: https://www.toppr.com/ask/question/two-spheres-of-same-size-are-made-of-the-same-metal-but-one-is-hollow/ I think it is...
  19. K

    B Two points of contact in rolling

    Suppose a sphere is rolling on horizontal surface. The point of contact is the instantaneous center of rotation. It's velocity momentarily is zero. So in a time dt it'll stay where it is. However during this time dt the point next to this contact point at its right side will move forward and...
  20. T

    Line of charge and conducting sphere (method of images)

    I was thinking of using the sphere and point charge as an analog, but is quite diferent from what i have seen
  21. milkism

    A diamagnetic sphere in a uniform magnetic field

    Problem: Solution part a) where formula 6.14 is just M x n. We need to do part b without seperation of variables, I'm quite stuck. Will B just be the magnetic field inside a solenoid? How can I find the other fields.
  22. MatinSAR

    Density of a sphere that has a cavity

    The sphere floats on water so we should have: ##F_b=F_g## The buoyant force is equal to the weight of the displaced fluid, so : ##\rho _wV_wg=\rho _sV_sg## (w: water, s: sphere) From last equation we have : ##V_w=\frac {\rho _s}{\rho _w} V_s \rightarrow V_w=5 V_s ## The volume of displaced...
  23. B

    B Mapping wave forms to sphere, does wave form y=0 have a reflection?

    Zero does not have an inverse. And y=0 does not have an inverse. Does the wave form y=0 for all x have an inverse?
  24. B

    I Faraday's Nested Sphere Experiment

    Hi there! I have a question about the Faraday's Nested Sphere Experiment, please see the attached pdf. I wonder why equation (1) and the electric field's equation ( coming after (1) ) consider only the charge Q. Why there aren't charge -Q in the equation? Ps. I'm thinking about point charges...
  25. I

    A Finding Minimal Mean Distance Curves on the Unit Sphere

    **Problem:** Find parametric equations for a simple closed curve of length 4π on the unit sphere which minimizes the mean spherical distance from the curve to the sphere; the solution must include proof of minimization. Can you solve this problem with arbitrary L > 2π instead of 4π? There...
  26. Wrichik Basu

    I Understanding Ewald's sphere in the context of X-Ray diffraction

    ##\require{physics}##I am trying to understand how the Ewald's sphere works in the context of X-ray diffraction (XRD). I am reading from Kittel's book, as well as a few lecture series. Let me first state what I have learnt in this context (please correct me if I am wrong). For any real lattice...
  27. P

    I Finite many Lattice Points in Sphere?

    Hello, I am wondering if in an n-ball the number of lattice points is finite. First, we have a ball which is bounded by the radius. The distance between two lattice points is given by the successive minimum. Theoretically, one could now draw a ball* around each lattice point in the (big)...
  28. Quasar100

    Normal Forces on a Sphere in a Non-vertical Groove

    neglect friction and motion (sliding) and G(sphere)=20N. In this question I reached two different result with two different solving method.But one of them is false according to answer key. My question is why first solving way is false? Because the first solution way makes sense to me. If we...
  29. Lars Ph

    I Use the Ewald sphere to calculate h,k,l?

    How do I use the ewald sphere to calculate h, k and l?
  30. Lars Ph

    I Use the Ewald sphere to calculate h,k,l?

    I am unsure wether or not all I can use the Ewald sphere for is to calculate d_hkl for the diffracted wave vector. For cubic lattices for example d= a/sqrt(h^2+k^2+l^2). To determine the lattice constant "a" you would then need to know exactly what your h,k and l are or you use lattice-dependent...
  31. Twigg

    Reducing friction at interface between a sphere and a plane?

    I have a flat planar part made of crystalline sapphire (about ~2k weight, and polished to a mirror finish) that rests on three ball bearings, and I want to minimize the static friction at these 3 interfaces. The ball bearings are fixed so they cannot roll, and the sapphire part can only slip...
  32. Pushoam

    Calculating Volume of a Sphere Using Integration: What Mistakes Have I Made?

    I consider a disc of thickness ## R d\theta ## as shown in the figure. Then, $$ dV = \pi R^2 sin^2 \theta R d\theta $$ ( Area of the disc * its thickness) Hence, $$ V = \int^{\pi}_{0} \pi R^2 sin^2 \theta R d\theta $$ $$ V = \frac 1 {2} {\pi}^2 R^3 $$ ....(1) While $$ V =...
  33. dom_quixote

    B Geometric Issues with a line, a plane and a sphere...

    I - A point divides a line into two parts; II - A line divides a plane into two parts; III - Does a smaller sphere divide a larger sphere into two parts, like layers of an onion? Note that the first two statements, the question of infinity must be considered. For the third statement, is the...
  34. Addez123

    Calculate surface integral on sphere

    I'm supposed to do the surface integral on A by using spherical coordinates. $$A = (rsin\theta cos\phi, rsin\theta sin\phi, rcos\theta)/r^{3/2}$$ $$dS = h_{\theta}h_{\phi} d_{\theta}d_{\phi} = r^2sin\theta d_{\theta}d_{\phi}$$ Now I'm trying to do $$\iint A dS = (rsin\theta cos\phi, rsin\theta...
  35. I

    Flux through top part of sphere

    Flux=$$\iint(xz, -yz, y^2)\cdot(x,y,z)/\sqrt{2} dA=\int_0^{2\pi}\int_0^1 r^2\cos^2\theta \sqrt{1-r^2/2} rdrd\theta$$. Integrating this doesn't give the correct answer of ##\pi/4##.
  36. N

    Find the charge of the sphere (q2)

    I drew a diagram using all of the information however, I am stuck and not to sure how to get one of the charges
  37. J

    Hollowed out sphere exerting gravitational force

    I solved that the hollowed out mass is M/8, which is correct. I don't understand why it is incorrect to substitute the remaining mass (7M/8) back into the F = G*m1m2/r to produce the force. Why is the solution the force of the whole lead sphere minus the force of the “hole” lead sphere, which is...
  38. T

    Electric Potential of a Sphere: A Puzzling Problem

    I can calculate the electric field strength at any point above the plane with Gauss' Law (##E = \frac{\eta}{\varepsilon_0}##) and so the electric potential at any point a perpendicular distance ##z## above the conducting plane (##V=−\frac{\eta}{\varepsilon_0}z##). But I'm having trouble taking...
  39. M

    I Effect of time on density distribution+shape of uniformly dense sphere

    I agree with Doc. Al that, "For the simplified case of a uniform density spherical planet, the gravitational field varies linearly from 0 at the center to its full value at the surface." But, what is the effect, if any, on the shape and density distribution of such a sphere over time (e.g...
  40. squeekymouse

    B How to understand the steradians equation for measuring a sphere of light?

    Hello and please know I am very greatful for your help! I am wanting to learn how to measure light. I have chosen a specific light for this to help me better understand. Lm- 7800 CD-620.7 So, I got that far, lol. I don't really know how to input the numbers for the Steradians equation, I have an...
  41. lavalite

    Thin-walled sphere and fluid mechanics question

    Suppose you had a thin-walled sphere fully submerged in a liquid. The sphere is filled to the equator with a liquid of sufficient density to reach buoyant equilibrium. Will the lateral cross-sectional areas of the thin-walled sphere experience tensile stresses in the longitudinal axis? Why or...
  42. Rikudo

    Gravitational field of a hollow sphere

    Why the area of the thin rings are ##2πasin\theta \, ds##? (a is the radius of the hollow sphere) If we look from a little bit different way, the ring can be viewed as a thin trapezoid that has the same base length ( ##2πa sin\theta##), and the legs are ## ds##. The angle between the leg and...
  43. tbn032

    B Rolling of non-deforming sphere on a non-deforming rough surface?

    According to my current understanding rolling friction rolling friction is the static friction (parallel to the surface on which the object is moving) applied by the frictional surface (rough surface) on the contact point or contact area of the object whose v≠Rw(v is translational velocity and...
  44. tbn032

    B Friction on pure rolling non deforming sphere?

    How will the friction work on a sphere which is purely rolling on a horizontal surface such that both the sphere and surface does not deform. The sphere at any time t will only have one point of contact, which would continuously changing as the sphere rolls. Will The friction be applied to the...
  45. Jenq

    A Pressure balance in a sphere

    Hi A sphere with radius r is buried in an elastic ideal medium at pressure P1. Inside the sphere I use energy E to create a variation of pressure of dP. What variation dPx I would measure if the sphere was buried in a medium at pressure P2 using the same energy E? Is it possible to solve...
  46. Addez123

    Why Does My Integration Over a Sphere Give Incorrect Results?

    ##\iiint 3 dr d\rho d\phi## The volume of a sphere is ##4\pi /3 r^3## so naturally the answer is ##4 \pi R^3## But when I integrate I do: ##3 \iint r |_0^R d\rho d\phi## ##3R \int \rho |_0^{2\pi} d\phi## ##6R\pi * \phi |_0^\pi = 6R\pi^2## What am I doing wrong?
  47. LCSphysicist

    A radially pulsating charged sphere creates which of these effects?

    I know that (a) is right, and (b) is wrong. The problem is with (c)... It seems correct to me! I can't see how this is not true. The electric charge o the sphere by itself will create an electric field, which will move the particle.
  48. S

    The angle at which a skier will leave the sphere

    Back here again.. but I am sorry guys, only the parameters are on my paper so wouldn't be of much help to show. I basically have no clue on how to start solving this problem at all. I stopped yesterday and let it sit overnight but still have no clue on how to approach the problem basically...