function f = beam_dynamic_external_force (t)
% ƒr�[ƒ€‚É�ì—p‚·‚éŠO—Í
    % �³Œ·”g
    %f = 5 * sin(2*pi*t);
    % ƒXƒeƒbƒv
    f = 5 * (t <= 2);
end
