在研究物体的相对运动时,参照物的选择是任意的.我们习惯于选择地面或相对于地面静止的物体为参照物,但有时选择相对于地面运动的物体为参照物可能会使解题过程变得简单、方便、快捷.下面简单举例来说明.例1一艘船在河中逆流而上,河水流速为3米/秒,经过一座桥时,船上一只木箱掉 When studying the relative motion of an object, the choice of the reference object is arbitrary. We are used to selecting the ground or an object that is stationary relative to the ground as a reference object, but sometimes selecting objects that move relative to the ground as a reference object may make the problem-solving process possible. It is simple, convenient, and fast. Here is a simple example to illustrate. Example 1 A ship is moving upstream in a river with a river flow rate of 3m/s. When a bridge passes, a wooden box on the ship goes off.