  We investigate the geometrically nonlinear deformation and buckling of a
slender elastic beam subject to time-dependent `fictitious' (non-inertial)
forces arising from unsteady rotation. Using a rotary apparatus that accurately
imposes an angular acceleration around a fixed axis, we demonstrate that
centrifugal and Euler forces can be combined to produce tunable structural
deformation. Specifically, using an imposed acceleration ramp, the buckling
onset of a cantilevered beam can be precisely tuned and its deformation
direction selected. In a second configuration, a pre-arched beam can be made to
snap, on demand, between its two stable states. We also formulate a theoretical
model rooted in Euler's elastica that rationalizes the problem and provides
predictions in excellent quantitative agreement with the experimental data. Our
findings demonstrate an innovative approach to programmable actuation of
slender rotating structures.
