Baseball and string activity to find the surface area of a sphere

Estimated Time
1 hour

Prerequisites/Instructions, prior preparations, if any
Circles should have been covered.

Materials/ Resources needed
Non digital: Baseballs, string, marker pens, scale, scissors and chart paper

Digital: Computer and projector

This activity has been taken from the website ehow.com

Process (How to do the activity)
To understand the formula $$4πr^2$$ for deriving surface area of a sphere :
 * Process:
 * 1) Divide the class into groups and give each group a baseball and string.
 * 2) Ask the students to lay flat the string around the widest part of the baseball and mark.
 * 3) The meaured length would be the circumference.
 * 4) The measurement will be divided by pi to find the diameter (Remember: circumference/diameter = pi).
 * 5) The diameter divided by 2 would be the radius. Note down the radius.
 * 6) Now take a long piece of string and carefully wind it around the entire surface of the ball taking care not to overlap.Cut and discard the extra string.
 * 7) Next unwind the string,measure it using a measuring tape. This measure would be teh surface area of the sphere.
 * 1) Consider the length of string obtained from step 7, divide it into exactly 4 equal parts.
 * 2) Make a circle with each part. Measure the radii.( Hint: Can draw circle of radius from step 5 and lay the string around it)
 * 3) Observe that 4 circles would be equal and the radii in all 4 cases would be the same as the radius of sphere (derived initially by measuring circumference).
 * 4) The length of string covering the entire surface area of the sphere has been formed into 4 circles of equal radius.
 * 5) The area of 1 circle is $$ πr^2$$
 * 6) The area of 4 such circles would be 4 times the area of such circle.
 * 7) Hence teh area of a sphere would be $$4πr^2$$
 * Developmental Questions
 * Evaluation
 * Question Corner