Misconceptions

#	Misconception	Reality	Why Students Get It Wrong
1	"A soap bubble has excess pressure 2S/R"	$\Delta P$ = 4S/R for bubble (two surfaces); 2S/R is for a liquid drop	Forgetting inner surface of bubble
2	"Terminal velocity is proportional to radius r"	v_t ∝ $r^{2}$ (quadratic); ratio of v_t = ratio of $r^{2}$	Misreading the formula
3	"Strain has units of Pa"	Strain is dimensionless ( $\Delta L$ /L); only stress has unit Pa	Confusing stress with strain
4	"All three elastic moduli have different dimensions"	Y, B, and G all have dimensions [ $M^{1}$ $L^{-1}$ $T^{-2}$ ] (Pa)	Thinking they measure different "types" of quantity
5	"Bernoulli's equation works for any fluid flow"	Valid only for ideal (non-viscous, incompressible) steady streamline flow	Over-generalising the principle
6	"Mercury rises in glass capillary tubes"	Mercury is depressed (θ > 90°, cosθ < 0), not raised	Not considering contact angle for mercury
7	"The elastic limit is the same as the proportional limit"	Proportional limit < Elastic limit on the stress-strain curve	Conflating two distinct points
8	"Volume expansion coefficient β = 2α"	β = 3α (not 2α); area coefficient = 2α	Confusing area and volume expansions
9	"Pascal's law means pressure is highest at the input piston"	Pressure is uniform throughout the enclosed fluid	Misunderstanding force ≠ pressure
10	"Stefan-Boltzmann law can use temperature in Celsius"	T must be in Kelvin; P = σ $AT^{4}$ requires absolute temperature	Not converting to Kelvin