25 flashcard terms for AP Physics 2 Unit 1, written to match the course framework. Read them here, drill them as flashcards, or take the 25-question quiz. Free, no account needed.
P + ½ρv² + ρgh = constant along streamline. Higher velocity → lower pressure. Explains lift, atomizers, venturi tubes.
Pascal's Principle
Pressure applied to enclosed fluid transmitted undiminished throughout. Enables hydraulic systems (pressure distributed equally).
Surface Tension
Cohesive forces at liquid surface create 'elastic' behavior; enables insects to walk on water, creates droplets, capillary action.
Viscosity
Fluid's resistance to flow; molasses high viscosity, water lower. Viscous drag F = 6πηrv (Stokes' law) proportional to velocity.
Unit 1 Summary
Pressure increases with depth; buoyant force enables floating/sinking analysis. Fluid flow (continuity, Bernoulli) relates velocity/pressure. Practical: hydraulics, pumps, lift.
Gauge vs Absolute Pressure
Absolute pressure P_abs = P_atm + P_gauge. A tire gauge reading 200 kPa means the air inside is at ~301 kPa absolute; hydrostatic P = P₀ + ρgh gives absolute pressure only if P₀ is atmospheric.
Force on a Submerged Wall
Pressure varies with depth, so total force on a vertical dam face of height H and width w is F = ½ρgH²w (average pressure ½ρgH times area Hw). Doubling depth quadruples the force.
Apparent Weight in Fluid
A submerged object reads W_apparent = W − F_b on a scale. The scale supporting the fluid container reads more by exactly F_b (Newton's third law on the fluid).
Hydraulic Lift Energy Check
Pascal gives F₂ = F₁(A₂/A₁), but the small piston must move A₂/A₁ times farther, so W = F·d is the same on both sides. Force is multiplied; energy is not.
Volume Flow Rate
Q = Av measured in m³/s. Mass flow rate is ρQ. In a branching pipe, the sum of Q into a junction equals the sum of Q out — a fluid analog of Kirchhoff's junction rule.
Torricelli's Theorem
Fluid exits a small hole a depth h below the open surface with v = √(2gh), from Bernoulli with equal surface and exit pressure and negligible surface speed. Same speed as free fall through h.
Venturi Meter
Pressure difference between wide and narrow sections measures flow: ΔP = ½ρ(v₂² − v₁²). Manometer height difference Δh gives ΔP = ρ_fluid g Δh directly.
Steady, incompressible, nonviscous, irrotational flow along a streamline. Real pipes lose pressure to viscosity, so measured downstream pressure is always somewhat below the Bernoulli prediction.
Static Fluid at Same Height
In a connected, static fluid of one density, all points at the same height share the same pressure regardless of container shape — the hydrostatic paradox. Only depth below the free surface matters.
Manometer Reasoning
U-tube: P_gas = P_atm + ρg(Δh) when the open arm is higher, minus when lower. Different liquids in one tube are matched at the interface height, then ρ₁h₁ = ρ₂h₂ for the two arms above it.
Floating and Load
Extra load ΔW on a floating object sinks it by Δh where ρ_fluid g A Δh = ΔW (A = waterline area). Ships with a wide waterline sink less per tonne of cargo.
Buoyancy in Accelerating Frames
In an elevator accelerating upward at a, effective g becomes g + a; both weight and buoyant force scale up equally, so a floating fraction is unchanged but the apparent buoyant force increases.
Air Buoyancy on Balloons
A helium balloon rises because ρ_air g V exceeds the total weight (gas + envelope + payload). Net lift = (ρ_air − ρ_He) g V − W_envelope; lift shrinks at altitude as ρ_air drops.
Pressure Is a Scalar
Pressure has no direction; force from pressure acts perpendicular to any surface it touches. This is why the buoyant force on any shape reduces to the weight of displaced fluid.