Let us say P for plane, G for ground, O for object.

我们定义 P 是平面,G 是地面,O 是物体

耶鲁公开课 - 基础物理课程节选

For example, we know that if a body is near the surface of the Earth, the force of gravity of that object seems to be m times g, where g is 9.8.

例如,我们知道,如果在地球表面有一个物体,该物体受到的重力大小为 m 与 g 的乘积,g 等于 9.8

耶鲁公开课 - 基础物理课程节选