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S 1: a 1-sphere is a circle of radius r; S 2: a 2-sphere is an ordinary sphere; S 3: a 3-sphere is a sphere in 4-dimensional Euclidean space. Spheres for n > 2 are sometimes called hyperspheres. The n-sphere of unit radius centered at the origin is denoted S n and is often referred to as "the" n-sphere. The ordinary sphere is a ...
A closed n-ball of radius r is the set of all points of distance less than or equal to r away from x. In Euclidean n -space, every ball is bounded by a hypersphere . The ball is a bounded interval when n = 1 , is a disk bounded by a circle when n = 2 , and is bounded by a sphere when n = 3 .
a 1-sphere is a circle of radius centered at , and is the boundary of a disk ( -ball). a 2 -sphere is an ordinary 2 {\displaystyle 2} -dimensional sphere in 3 {\displaystyle 3} -dimensional Euclidean space, and is the boundary of an ordinary ball ( 3 {\displaystyle 3} -ball).
where S n − 1 (r) is an (n − 1)-sphere of radius r (being the surface of an n-ball of radius r) and dA is the area element (equivalently, the (n − 1)-dimensional volume element). The surface area of the sphere satisfies a proportionality equation similar to the one for the volume of a ball: If A n − 1 ( r ) is the surface area of an ( n ...
r is the radius of the sphere, h is the height of the cap, and; sr is the unit, steradian, sr = rad 2. Because the surface area A of a sphere is 4πr 2, the definition implies that a sphere subtends 4π steradians (≈ 12.56637 sr) at its centre, or that a steradian subtends 1/4π ≈ 0.07958 of a sphere.
The sphere's radius is taken as unity. For specific practical problems on a sphere of radius R the measured lengths of the sides must be divided by R before using the identities given below. Likewise, after a calculation on the unit sphere the sides a, b, and c must be multiplied by R.
A sphere of radius r has surface area 4πr 2.. The surface area (symbol A) of a solid object is a measure of the total area that the surface of the object occupies. [1] The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of arc length of one-dimensional curves, or of the surface area for polyhedra (i.e., objects with ...
The 3-sphere is naturally a smooth manifold, in fact, a closed embedded submanifold of R 4. The Euclidean metric on R 4 induces a metric on the 3-sphere giving it the structure of a Riemannian manifold. As with all spheres, the 3-sphere has constant positive sectional curvature equal to 1 / r 2 where r is the radius.