请帮忙翻译这个句子～～ 物理好的同学帮我解释解释～
two-dimensional motion can result when the acceleration vector is not along the line of initial motion. in the horizontal projectile motion, the acceleration vector due to the gravity is initially perpendicular to its motion
这是一道物理题的答案。题目是：under what condition can you have two-dimensional motion with a one-dimensional acceleration?