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

Objectives
Content objectives - what content areas

Skill objectives - what specific skills

Classroom objectives - to demo peer learning, to make a classroom resource, etc -

All these kinds of objectives need not be there for every activity. And no need to list them as different headings. This is only for our reference when we are developing activities.

Estimated Time
1 hour

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

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

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