/* compute change in velocity, i.e., dv = F * dt / mass velocity update using explicit Euler formula */ dv = dtime * force / 50.0; 速度的微分等于时间微分成立力除以质量(我赌5毛钱,质量是50.0kg) v_prev += dv;速度等于速度微分的累加 Message ("time = %f, x_vel = %f, force = ...