Fluids
Airplane wing
This prescribed flow field, not wing curvature or equal transit time, supplies the faster upper flow and its pressure difference.
Airplane wing — interactive physics simulation. This prescribed flow field, not wing curvature or equal transit time, supplies the faster upper flow and its pressure difference.
Lift from flow
This idealized flow model links a pressure difference across an airfoil to upward lift.
The prescribed flow field has faster air above the wing and lower pressure there. It illustrates a pressure-difference contribution to lift; it does not assume that air parcels must arrive together.
- P + ½ρv² = constant
- Lift ∝ ΔP · area
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
Air flows faster over the curved top of an airfoil than underneath it. According to Bernoulli's principle, which surface has lower pressure — and what does that mean for the wing?
Predictions to weigh
- The top surface has lower pressure, creating a net upward force (lift).
- The bottom surface has lower pressure, pushing the wing down.
- Both surfaces have equal pressure, so there's no net force.
Variable roles
What you set:
- Bottom-path area A₁ (m²)
- Top-path area A₂ (m²)
- Inlet air speed v₁ (m/s)
What you measure:
- Top-surface speed v₂ (m/s)
- Pressure difference ΔP (top − bottom) (kPa)
How the investigation runs
- Open the fluid-wing preset and press Reset. Air flows over an airfoil cross-section; the top-surface path is narrower than the bottom, so air speeds up over the top.
- Enable the top-surface-speed and pressure-difference readouts.
- Set the bottom and top cross-sectional areas and the inlet air speed for each trial, and record the top speed and pressure-difference readings.
Governing equation
Continuity Equation — A₁·v₁ = A₂·v₂
For an incompressible fluid, the flow rate (area × speed) is conserved along a streamline: A₁v₁ = A₂v₂. The narrower path over the top of the airfoil forces the air there to move faster.
Bernoulli's Equation (air) — P₁ + ½ρv₁² = P₂ + ½ρv₂²
Along a horizontal streamline, P + ½ρv² stays constant. Air moving faster over the top of the wing has lower pressure there than the slower air underneath — the pressure difference that contributes to lift.
What the printable worksheet asks students to work out
- For one trial, compute v₂ = A₁v₁/A₂ from continuity, then ΔP = P_top − P_bottom = ½ρ_air(v₁² − v₂²) using air density 1.225 kg/m³. Compare both to the readings — ΔP is negative because the faster air over the top sits at lower pressure, and that is what lifts the wing.
- The pressure difference here is much smaller in Pa than in the fluid-venturi experiment for similar speeds. Explain why, using the density value in Bernoulli's equation.
Where this shows up beyond the lab
- This model (continuity + Bernoulli) explains part of how wings generate lift, but real aerodynamic lift also depends heavily on the wing's angle of attack, and does not require air parcels above and below the wing to arrive at the trailing edge together. Why might a simple 'equal transit time' story about lift be misleading?
- Air density drops at high altitude. Using ΔP = ½ρ_air(v₁² − v₂²), explain why a wing needs to move faster through thin high-altitude air to generate the same lift it would at sea level.
- AP Physics 1 — Unit 8: Fluids
- General High School Physics — Fluids & pressure
- NGSS High School Physics — Forces and Newton's second law
- Welcome to Fluid Wing
- Press Play
- Pressure difference
- Open the Properties panel
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.