TITLE: Difference of surface tension on area of same surface
QUESTION [0 upvotes]: Last day I was doing an experiment about surface tension phenomenon of water.
I had a floated bussiness card on surace of water near edge of container and some drops of detergent- container was big enough, thus card had abillity of moving on the surface. No heat had been given to liquid(water).
I added on drop of detergent to water surface in a point close to card. The card escaped from that point; water pulled it to the opposite edge of the bowl.
I was wondering if anyone can help me knowing the reason of this happening.
Thank you.
Best regards

REPLY [0 votes]: This is an example of the Marangoni effect and the Khan Academy video is very informative.
By adding detergent ot the water the surface tension in the proximity of the detergent is reduced and the rest of the water surface actually pulls the card as it reduces its surface area where the surface tension is larger.
That reduction in surface area of the water is accompanied by a liberation of energy (which was used to create the water surface in the first place) and so the card gains kinetic energy.
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