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Capillary Action

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State

Capillary action is a liquid's rise up a narrow tube against gravity, from adhesion to the walls outcompeting the liquid's own cohesion.

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A blood drop is drawn up a narrow glass tube during a fingerstick, since adhesion to the glass exceeds cohesion.

Watch for

A liquid rises only where adhesion exceeds cohesion — mercury's stronger cohesion makes it dip instead.

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