Is the downward force of gravity, the push of the slide (upward perpendicular to the surface) and friction and air forces resisting forward motion.

• 如学生玩滑梯,同时存在向下的重力,滑梯产生的举力(与表面垂直并向上)和阻止身体向前运动的摩擦力和空气的阻力。