Surface tension problems and lab work
Answers are for parents and teachers.
1
By how many mm does water rise in a 0.2 mm radius capillary? (σ = 0.073; g = 10)
about 73 mm
2
A dropper has inner diameter 3 mm. Estimate the mass of one drop (σ = 0.073; π = 3.14; g = 10).
about 6.9·10⁻⁵ kg
3
With what force does a soap film (σ = 0.04 N/m) pull the 10 cm side of a frame?
2·0.04·0.1 = 8·10⁻³ N
4
In the lab F = 0.030 N and l = 0.40 m. Find σ and compare with the water table value.
σ = 0.075 N/m, close to the table value 0.073.
5
Why does an insect walking on water not sink?
The surface tension force balances its weight and its legs are not wetted by water.