A cube, one of the five platonic solids, is a three-dimensional solid with 6 congruent square faces. Thus it is a hexahedron (hex means six, hedron means face). It is also considered a special type of square prism. The diagram shows the shape of a cube.
Cube
Ice cubes, dice, and Rubik’s cube are some common examples of cube shaped objects in real life.
Parts of a Cube
The parts of a cube are:
6 Faces – Opposite faces are parallel. Every face meets other four faces. The angles between any two faces are 90°.
8 Edges – Opposite edges are parallel
12 vertices – Each vertex is the meeting point of three faces and three edges.
A net of a cube can help us understand its shape from a 2-D view as shown.
Cube Net
Formulas
Surface Area
Surface Area or Total Surface Area (TSA)= 6a2, here a = edge
Lateral Surface Area (LSA)= 4a2 (this is inclusive in TSA)
So, TSA = LSA + 2a2 = 6a2
Let us solve an example to understand the concept better.
Find the lateral and total surface areas of a cube with a side of 4 in.
Solution:
As we know, Lateral Surface Area (LSA)= 4a2, here a = 4 in ∴ LSA = 4 × (4)2 = 64 in2 Total Surface Area (LSA)= LSA + 2a2, here a = 4 in ∴ TSA = 64 + 2 × (4)2 = 96 in2
Find the surface area of a cube with a side length of 5 cm
Solution:
The side length is actually the length of the edge. So, Total Surface Area (TSA)= 6a2, here a = 5 cm = 6 × 52 = 150 cm2 Volume Volume (V) = a3, here a = edge
Calculate the volume of a cube of 6 cm.
Solution:
As we know, Volume (V) = a3, here a = 6 cm ∴ V = 63 = 216 cm3
Diagonal
There are two types of diagonal in a cube – space diagonal, and body diagonal. The space or bodydiagonal of a cube is the main diagonal passing through the center in the inner space. The face diagonal is the diagonal on each of its faces.
The formulas are:
Face Diagonal = ${\sqrt{2}a}$
Space Diagonal (d) = ${\sqrt{3}a}$
Find the length of the main diagonal of a cube whose edge is 7 cm.
Solution:
As we know, The main diagonal is the body diagonal. So, the length of the diagonal is: Length of Space Diagonal (d) = ${\sqrt{3}a}$, here a = 7 cm d = √3 × 7 ≈ 12.12 cm
Finding the VOLUME of a cube when the DIAGONAL is known
Find the volume of a cube whose diagonal is 6 cm
Solution:
Here we will use an alternative formula for volume involving the diagonal. V = ${\dfrac{\sqrt{3}}{9}d^{3}}$, here d = 6 cm ∴ V = √3 × 63/9 ≈ 41.57 cm3
