A sphere is a perfectly round three-dimensional object. Every point on its surface is at the same distance (radius) from its center.
A sphere is a 3D analog of the circle. It is the set of all points in three-dimensional space at a fixed distance (radius) from a center point. The sphere has the smallest surface area for a given volume of any shape.
For a hemisphere (half of a sphere):
Volume: V = (4/3) · π · 6³ = (4/3) · π · 216 = 288π ≈ 904.779 cm³
Surface area: A = 4 · π · 6² = 4 · π · 36 = 144π ≈ 452.389 cm²
Hemisphere volume: V_hemi = (2/3) · π · 216 = 144π ≈ 452.389 cm³
The Earth is approximately a sphere (actually an oblate spheroid). The sphere is the most volume-efficient shape — it contains the maximum volume for a given surface area. This is why soap bubbles form spheres.