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From Karnataka Open Educational Resources
Baseball and string activity to find the surface area of a sphere (view source)
Revision as of 11:22, 24 May 2019
, 11:22, 24 May 2019→Estimated Time
===Estimated Time===
===Estimated Time===
1 hour
=== Prerequisites/Instructions, prior preparations, if any ===
=== Prerequisites/Instructions, prior preparations, if any ===
Circles should have been covered.
===Materials/ Resources needed===
===Materials/ Resources needed===
Baseballs, string, marker pens, scale, scissors and chart paper
===Process (How to do the activity)===
===Process (How to do the activity)===
*Process:
#Divide the class into groups and give each group a baseball and string.
#Ask the students to lay flat the string around the widest part of the baseball and mark.
#The meaured length would be the circumference.
#The measurement will be divided by pi to find the diameter (Remember: circumference/diameter = pi).
#The diameter divided by 2 would be the radius. Note down the radius.
#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.
#Next unwind the string,measure it using a measuring tape. This measure would be teh surface area of the sphere.
To understand the formula <math>4πr^2</math> for deriving surface area of a sphere :
#Consider the length of string obtained from step 7 , divide it into exactly 4 equal parts.
#Make a circle with each part. Measure the radii.''( Hint: Can draw circle of radius from step 5 and lay the string around it)''
#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).
#The length of string covering the entire surface area of the sphere has been formed into 4 circles of equal radius.
#The area of 1 circle is <math> πr^2</math>
#The area of 4 such circles would be 4 times the area of such circle.
#Hence teh area of a sphere would be <math>4πr^2</math>
*Developmental Questions
*Evaluation
*Question Corner
