Error Analysis — Common Mistakes Table — Notes

#	Common Error	What Students Do Wrong	Correct Approach	Key Distinction
1	Drop vs bubble pressure	Use 2S/R for both	$\Delta P$ = 2S/R (drop, 1 surface); $\Delta P$ = 4S/R (bubble, 2 surfaces)	Count free surfaces
2	Terminal velocity proportionality	Assume v_t ∝ r (linear)	v_t ∝ $r^{2}$ (quadratic); doubling r → 4× v_t	Check $r^{2}$ in formula
3	Strain units	Give strain in Pa or m	Strain is dimensionless ( $\Delta L$ /L ratio)	No units for strain
4	Elastic vs plastic region	Mark yield point as elastic limit	Elastic limit comes before yield point on stress-strain curve	Curve sequence order
5	Bernoulli's applicability	Apply to viscous / compressible fluids	Valid only for ideal (non-viscous, incompressible) steady flow	Check assumptions
6	Capillary rise sign	Ignore contact angle direction	Rise (θ < 90°, concave), Depression (θ > 90°, convex)	Sign of cosθ
7	Pascal's law confusion	Think pressure increases with area	Pressure is same throughout enclosed fluid, force scales with area	P same, F = PA different
8	Compressibility vs Bulk modulus	Treat them as same or equal	Compressibility = 1/B; high B → low compressibility	Reciprocal relationship
9	Thermal expansion relations	Assume β = 2α	β (volume) = 3α; area coefficient = 2α	Factor of 3 for volume
10	Stefan-Boltzmann law	Use T in °C	T must be in Kelvin (absolute temperature) in P = σ $AT^{4}$	Always use Kelvin