Summarize the following:
A globe or ball (sphere) can work also, but it's harder to measure. Circumference | diameter | quotient C / d =? __________|________|__________________ __________|________|__________________ __________|________|__________________ __________|________|__________________ Mark the distance one time around it on the string. This is the circumference: it's just like perimeter, but, the perimeter of a circle--the distance around a circle--is called the circumference, not perimeter, usually. Write down your measurement of the circumference using decimals. Pin or tape the ends of the string for measuring it accurately (straight and extended to its full measure), since you would have needed to tighten the string around the circular object, so now you would tighten it lengthwise. This is the diameter. Note: Multiplying two times radius, i.e.: "2 X radius = diameter" is also written as "2r = d". The four division problems of C / d = _____, should be about 3 or 3.1 (or about 3.14 if your measurements are accurate); so what is pi: It's a number. It's a ratio. It relates diameter to circumference. Of course, using precise measurements using dividers, which are similar to a compass can help. 3.1 + 3.15 + 3.1 + 3.2 = ____ /4 = ____? That's 12.55 / 4 = 3.1375, and can be rounded-off to 3.14). That's the idea of "pi". The number of diameters that makes the circumference (all the time, so it's constant)... That is the constant "pi". That number of diameters. Also, the radius will fit a little more than 6 (2 times pi) times around a circle, as well as knowing that the diameter goes three times; so, that implies a circumference formula C = 2 X 3.14 X r, which is just = 3.14 X d ... by using 2r is d ("Got it", nod yes. "Yeah!" But, read and think over it again until it really soaks in, if it's not yet crystal clear). Do this for each of the containers. The left-over piece of string from each of the circumference strings cut-outs will be approximately the same length. The measurement length of this short piece of string should be .1415 which is just an example of getting approximately 3.14...
Number four different sizes of circular containers or lids. Get a non-stretchy, non-kinky string and a meter-stick, yardstick or ruler. Make a chart (or table) like the following one: Measure accurately around each of the four circular items by wrapping a string snugly around it. Straighten and measure the part of the string that you marked as the distance around the circle. Turn the container upside down so you can find and mark the center on the bottom so that you can measure the diameter using decimals (also called decimal-fractions). Measure across each circle exactly through the center of each of the four items with a straight edge measure (meter-stick, yardstick or ruler). Divide each circumference by the same circle's diameter. Average the four answers to the division problem by adding those four quotients and dividing by 4, and that should give a more accurate result (for example, if your four divisions gave you: Finally, take the diameter string and use it to cut its length off the circumference string three times.