As time increases, the angle increases and we can ask, "How long does it take for the particle to come back to the starting point?"

这个角度随着时间在增加,我们会问,"质点需要多长时间,才能转到起点"

耶鲁公开课 - 基础物理课程节选

This says, if you want to be in the air for a long time, so you may think that 90 degrees is the best angle.

也就是说,如果你想在空中停留更久,你也许会认为 90°是最佳选择

耶鲁公开课 - 基础物理课程节选