A soap film is held in a wire frame with one side a movable wire 8.0 cm long…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A soap film is held in a wire frame with one side a movable wire long. The surface tension is . What force holds the wire still? How much work stretches the film by moving the wire outward?
Need a reminder? The key ideaShow
Surface tension is force per unit length, or energy per unit area of surface, in . A film has two surfaces. Excess pressure: inside a drop or an air bubble in a liquid, inside a soap bubble.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Force. .
Step 2. Work. .
Answer: ; .
Check. New area , times , gives the same work.
Watch out. A film has two surfaces, so the force is , not .
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