straight line

详细解释:【机】 直线

英语解释：

名词 straight line:

a line traced by a point traveling in a constant direction; a line of zero curvature

例句：

The curve traced by a point on the circumference of a circle that rolls on a straight line.圆滚线，摆线圆周上任一点在一条直线上滚动时所形成的曲线