A supercell tornado (Burgers–Rott vortex) crosses a Great-Plains farmstead. Every building has a wind-load capacity, the pickup truck has a slide and a roll-over limit, and debris is carried by drag. Drive the truck, watch the barn, silo, windmill and fence fail one by one, then rate the tornado from the damage like a survey team does.
Sweeps a steady cross-wind from 20 to 110 m/s over the truck model and reports the wind speed where the tyres break away and where it tips, compared with the closed-form values.
The science
Wind field. Tangential wind is the Burgers–Rott vortex vθ(r) = Γ/(2πr) · (1 − e−r²/rb²), peak Vmax = 0.6382 Γ/(2π rb) at r = 1.1209 rb. Radial inflow ur = −a r/2 (flattened beyond 3 rb), updraught w = wmax tanh(a z/wmax), strain a = Vmax/(2 S rb). Near the ground the wind is reduced by friction (70 % at the surface rising to 100 % at 10 m, the height the EF scale refers to). The cyclostrophic pressure deficit Δp(0) = ρ (Γ/2πrb)² ln 2 is an upper bound; measured deficits are typically smaller.
Wind load on structures. A wall or roof feels F = ½ ρ Cd A v² with ρ = 1.2 kg/m³. The "capacity" shown in the survey table is that force at the failure wind speed listed for each object. Those failure speeds (fence 30 m/s, tree 38 m/s, windmill rotor 33 m/s and tower 48 m/s, farmhouse roof 40 m/s and walls 60 m/s, barn 44 m/s, silo 52 m/s) are illustrative values placed in plausible Enhanced-Fujita degree-of-damage bands, not engineering results: real failure depends on fastening, age, orientation and debris impact. The survey rates the tornado by the strongest failed indicator, the way EF ratings are actually assigned; an EF rating from damage can therefore be lower than the true peak wind if nothing strong was in the path.
Truck. Side force Fs = ½ ρ Cd,s As vrel² (Cd,s = 1.1, As = 4.4 m²) acts at height h = 0.95 m. Tyres hold while Fs < μ m g, so the slide speed is vslide = √(μ m g / (½ ρ Cd,s As)); the truck tips when the wind moment beats the weight moment, Fs h > m g t/2, i.e. vroll = √(m g t / (ρ Cd,s As h)) (t = 1.7 m track, m = 2400 kg). On wet asphalt (μ = 0.5) it slides first; once sliding faster than 6 m/s sideways it trips on the verge and rolls at 55 % of that moment. Vertical lift in the updraught, gust factors, suspension roll and the vortex's pressure drop are ignored. Vehicles are not safe shelter in a tornado: this is a physics lab, not safety advice.
Debris and flying structures. Each piece obeys dv/dt = k |u − v| (u − v) − g, k = ρ Cd A/(2m), integrated by exponential relaxation (stable at any frame rate). A destroyed barn (m ≈ 12 t, A ≈ 120 m²) has a terminal fall speed √(g/k) of about 27 m/s, a silo tank about 50 m/s, so they are thrown rather than lifted far; small boards and sheets rise much higher. Lift-off speeds and masses are illustrative.
Condensation funnel. The pressure drop cools rising air, ΔT ≈ κ T Δp/p (κ = 0.2857); air condenses where this exceeds the dew-point depression left after lifting. Dry air hides the funnel but not the wind: a funnel cloud is not the tornado, the wind is.
EF scale. 3-second-gust bands in mph (EF0 65–85, EF1 86–110, EF2 111–135, EF3 136–165, EF4 166–200, EF5 >200).
Checks. Burgers peak by bisection; Δp0 vs closed form vs Simpson; cyclostrophic balance by finite differences; drag integrator vs exact fall law; truck slide and roll-over speeds found by bisection on the simulated force/moment vs the closed forms; braking distance of the truck integrator vs v²/(2 μ g); flying-barn terminal speed.
Landscape, farm buildings, windmill, pickup and debris were modelled in Blender (Cycles-baked textures) and rendered with Three.js. Independent educational model; not affiliated with any vehicle maker.
Educational physics model. Inanimate objects only.