Physics Question

Question

A spherical soap bubble of radius & is formed by means of blowing through a small soapy blow pipe. If r = 6in & σ = 15 dyne 1cm, find the work input in overcoming the surface tension in the bubble.

Find the solution given that the answer is provided

W= 3.235×10^-3 ft-lbf .

Answer 1

Work required to create surface area:

W = sigma * (final area - initial area)

Taking the initial area as negligible:

W = sigma * 4*pi*r^2

Convert the radius:

r = 6 in = 0.5 ft

Convert surface tension:

1 dyne = 2.24809 × 10^-6 lbf

1 ft = 30.48 cm

sigma = 15 × (2.24809 × 10^-6) × 30.48

sigma = 1.02783 × 10^-3 lbf/ft

sigma ≈ 1.03 × 10^-3 lbf/ft

Calculate the work:

W = (1.03 × 10^-3) × 4*pi × (0.5)^2

W ≈ 3.236 × 10^-3 ft-lbf

This matches the answer:

W = 3.235 × 10^-3 ft-lbf