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USEFUL FORMULAE AND OTHER
DATA Areas of
Cross Section
Square: length of side'.
Rectangles: length x breadth
Parallelograms: base x perpendicular height.
Triangles: base by 1/2 perpendicular height.
Circles: square of diameters
x 7.854 = πD2/4
or π
r2 (Note π
= 3.1416)
Easy practical measurement: half circumference x half
diameter = area of circular section.
Annulus: Area = 0.785 (D2
‑d2) where D=
outer diameter and d = inner diameter.
Surface area:
a) of a ball, 3 x cross
section area (πD2/4
)
or 2.356D2.
b) Sloping surface of a cone, 1.571 diameter of base x sloping
height.
Volumes
Cube: length of side 3.
Prism: (a) Rectangular: multiple of the three sides (h x b x I).
(b) Triangular: area of triangular section x length (hxbxl/2)
Sphere: 0.5236 diameter3
Cylinder: area of circular
cross section x length = 0.785 D2 x I.
Cone: 0.2618 D2 x
vertical height (1/3 cylinder of same dimensions).
Weld costing and other
hints
One cubic inch of steel weld
metal weighs 0.2831bs.
Mild steel weighs 7.85
gm/cm3, Aluminium 2.7 gm/cm3.
Approximately 1.7kg of
electrodes are required to produce 1 kg of weld metal (loss is wastage
in stubs, slag etc.).
Standard general purpose
electrodes average the following numbers per kg:
2.00 mm x 250 mm ‑
120 4.00 mm x 380 mm ‑ 25
2.50 mm x 300 mm ‑
65 5.00 mm x 450 mm ‑ 11
3.25 mm x 380 mm ‑ 30
To fit a square into a
circle: side of square should be .707 x diameter ofcircle.
Doubling the diameter of a
pipe increases its capacity four times.
To determine pressure of
column of water: multiply height in ft. x.434 =Ibs/in2.
One cubic foot hold 6.25
imperial gallons (28.4 litres).
One gallon of water weighs
10 Ibis (4.54 kg).
One cubic metre holds 1,000
litres.
One litre of water weighs 1
kg.
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