题目内容：

英语翻译
the total time that an object is in motion from the time it is projected (thrown) upwards to the time it hits the ground is called the time of flight.the initial speed is sometimes called the speed of projection.
用翻译机翻译的,一眼就能看出来.直接忽略你的答案.
请人性化通俗易懂的描述一下.