Physics Demonstrations

Fluid Mechanics

Inlet Area (m^2)
Throat Area (m^2)
Inlet Velocity (m/s)

In this demonstration, we observe an ideal fluid flowing through a pipe that narrows at its midsection (a Venturi tube). Two fundamental principles govern the flow: the Continuity Equation and Bernoulli's Equation. Continuity Equation — for an incompressible fluid the volumetric flow rate is constant: $A_{1} v_{1} = A_{2} v_{2}$ So the fluid speeds up when the pipe narrows: $v_{2} = \frac{A_{1} v_{1}}{A_{2}}$ Bernoulli's Equation — for a horizontal, steady, inviscid flow the total mechanical energy per unit volume is constant: $P_{1} + \frac{1}{2} ρ v_{1}^{2} = P_{2} + \frac{1}{2} ρ v_{2}^{2}$ Solving for the pressure difference: $Δ P = P_{2} - P_{1} = \frac{1}{2} ρ (v_{1}^{2} - v_{2}^{2})$ Because speed increases in the throat, pressure decreases there — this is the Venturi effect. The animation shows particles (water, $ρ = 1000$ kg/m³) flowing through the pipe and bunching closer together in the narrow section, illustrating the increase in speed. The title displays the computed inlet velocity, throat velocity, and pressure difference. Some questions to consider while viewing the demonstration: As you decrease the throat area, what happens to the throat velocity and the pressure difference? If the throat area equals the inlet area, what does Bernoulli's equation predict for $ΔP$ ? Identify a real-world device or phenomenon that exploits the Venturi effect. What assumptions (ideal fluid, no viscosity, steady flow) could cause a real pipe to differ from these predictions?