FALLING CHIMNEY
A toppling chimney rotates, so its tip accelerates at (3/2)g·sinθ — past 42° that beats free fall, and the mortar tears at L/3 up.
Use the simulation above to change the variables and play through the guided stages. The explanation below describes the default starting values; the simulation updates its explanation as you experiment.
Setup
A tall brick chimney, demolished by knocking out its base — it hinges and topples like a felled tree. But watch a real one: it almost never falls in one piece. Somewhere on the way down it snaps in two, in mid-air. Why?
It rotates
It is not free-falling, it is ROTATING about its base — so every point moves on an arc, and the farther out, the faster it must accelerate. Energy sets the spin, torque sets the angular acceleration, and the two agree exactly.
Downward acceleration
The tip has tangential and inward-radial acceleration. Add those vectors, then take the vertical component: the true downward acceleration first exceeds g at 36.415°. The amber arrow shows that full vector, not a tangential proxy.
It snaps
In the ideal uniform-rod bending model, r(L−r)² peaks at L/3. Real rupture also depends on axial stress, cross-section, angle, and material, so the marker is a model prediction rather than a universal exact break height.
Audit
Audited: energy and torque agree; vector kinematics gives the true downward component and its 36.415° crossing; the ideal bending moment peaks at L/3 while real fracture height remains material-dependent.