You will need
  • • Ruler or tape measure.
  • • A pencil or marker.
  • • A sheet of paper or cardboard or other suitable object with right angles.
Suppose you have a water tank of cylindrical shape. You need to fill it with water, but you want to calculate the volume that it will fill.

From the school course of geometry you know that the formula of volume of cylinder is:

V = SH ,

that means, the volume of a cylinder equals the area of S is at its height H.

The height of the cylinder H to easily measure a tape measure or ruler.
Determine the height of the cylinder
Now, define the footprint. The area of a circle, as we know from school the geometry is determined by the formula:

S = πR2,

where π is the digit in mathematics the ratio of the lengths of the circumference and the diameter and is equal to 3.14159265...,

and R is the radius of the circle

How to calculate the area of a circle with only a ruler? Very simple!

From the same school course of geometry recall that any circle can be inscribed right triangle. Moreover, the hypotenuse of this triangle is equal to the diameter of the circle.

To do this, take a piece of cardboard or other suitable object having angles and imposed on our cylinder so that a right angle α with its tip And rests against the edge of the cylinder.
Fit the cylinder right triangle
Side of the rectangle that are intersected by the circle, mark it with a pencil or marker and connect with a straight line. In our case, the vertices of the triangle b and C. This cut is the diameter of our circle. The radius of the circle is equal to half its diameter. Divide the segment BC into two parts. The center of the circle is point O. the Segments Ob and OC are equal and are the base radius of the cylinder. Now substitute the obtained values into the formula:

V = πR2H
Defined by the base radius of the cylinder