Chemistry / Unit 8 Chem 1399 short lesson, about 20 seconds
Capillary Action
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The idea
Capillary action is a liquid's rise up a narrow tube against gravity, from adhesion to the walls outcompeting the liquid's own cohesion.
In practice
A blood drop is drawn up a narrow glass tube during a fingerstick, since adhesion to the glass exceeds cohesion.
Where people slip
A liquid rises only where adhesion exceeds cohesion — mercury's stronger cohesion makes it dip instead.
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