Length of a circle and diameter are the interconnected geometrical sizes. It means that the first of them can be transferred to the second without any additional data. A mathematical constant through which they are connected among themselves is the number π.
Instruction
1. If the circle is presented in the image form on paper, and its diameter is required to be determined approximately, measure it directly. If its center is shown on the drawing, draw through it a line. If the center is not shown, find it by means of compasses. For this purpose use the square with corners in 90 and 45 degrees. Apply it a 90-degree corner to a circle so that both legs concerned it, and circle. Having put then to the turned-out right angle a 45-degree corner of the square, draw a bisector. It will pass through the center of a circle. Then the same way draw the second right angle and its bisector in other place of a circle. They will be crossed in the center. It will allow to measure diameter.
2. For measurement of diameter it is preferable to use the ruler made of thinner sheet material or tailor's meter. In the presence of only a thick ruler measure diameter of a circle by means of compasses, and then, without changing its solution, transfer it to graph paper.
3. Also at absence and in the presence of only the drawing it is possible to measure circle length by means of the curvimeter in statements of the problem of numerical data, and diameter then to calculate. To use the curvimeter, in the beginning establish by rotation of its wheel an arrow precisely on zero division. Then note a point on a circle and press the curvimeter to a leaf so that the stroke over a wheel indicated this point. Carry out by a wheel in the area of a circle until the stroke appears over this point again. Read indications. They will be in centimeters - if necessary transfer them to millimeters.
4. Knowing the circle length (specified in statements of the problem or measured by the curvimeter), divide it into the doubled number π. Diameter expressed in the same units of measure as basic data will turn out. If it is required by conditions, transfer result of calculation to other, more convenient units.