A spherical soap bubble with a surface-tension of 0.005 lbf/ft is expanded from a diameter of 0.5 in to 3.0 in. How much work, in Btu, is required to expand this bubble

Answer:W = 1.23*10^-6BTU

Explanation: Work = Surface tension * (A1 - A2)

W = Surface tension * 3.142 * (D1^2 - D2^2)

Where A1 = Initial surface area

A2 = final surface area

Given:

D1=0.5 inches, D2 = 3 inches

D1 = 0.5 * (1ft/12inches)

D1 = 0.0417 ft

D2 = 3 * (1ft/12inches)

D2 = 0.25ft

Surface tension = 0.005lb ft^-1

W = [ (0.25) ^2 - (0.0417) ^2]

W = 954 * 10^6lbf ft * (1BTU/778lbf ft)

W = 1.23*10^-6BTU