Gravitational Freefall

引力自由下落

The freefall time and impact velocity for an object dropped from near the Earth can be calculated from simple trajectory equations if air friction can be neglected. But if the height is great enough for the acceleration of gravity to be significantly changed, then the calculation involves calculus to take into account the non-constant acceleration.

如果忽略空气摩擦，物体从地球附近下落的自由下落时间及冲击速度可通过简单的轨迹方程计算。但如果高度足够大，使重力加速度显著变化，则计算需涉及微积分以考虑非恒定的加速度。