Mechanical Properties of Fluids
Class 11 · Mechanical Properties of Fluids

Surface Tension

Excess pressure inside drops/bubbles — ΔP = 2T/R (drop), 4T/R (bubble).

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Key Notes

01

Surface tension T (N/m) is the force per unit length acting along a surface, minimising area.

02

Excess pressure inside a liquid drop: ΔP = 2T/R.

03

Excess pressure inside a soap bubble: ΔP = 4T/R (two surfaces).

Formulas

Drop

Single surface.

Bubble

Two surfaces (inner + outer).

Important Points

Smaller drops/bubbles have higher internal pressure — that's why two soap bubbles touching cause the smaller to push into the larger.

Water striders walk on water by exploiting surface tension.

Surface Tension notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 11 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.