运动描述

描述物体运动的参考物

保留质量这一主要因素

直角坐标系中：<br><span class="equation-text" data-index="0" data-equation="\vec r(t)=x(t)\vec i+y(t)\vec j+z(t)\vec k" contenteditable="false"><span></span><span></span></span><br><span class="equation-text" data-index="1" data-equation="|\vec r|=\sqrt {x^2+y^2+x^2}" contenteditable="false"><span></span><span></span></span><br><span class="equation-text" data-index="2" data-equation="cos\alpha=\frac{x}{|\vec{r}|},cos\beta=\frac{y}{|\vec{r}|},cos\gamma=\frac{z}{|\vec{r}|}" contenteditable="false"><span></span><span></span></span><br><br>

<span class="equation-text" data-index="0" data-equation="\Delta \vec r=\Delta r_x\vec i+\Delta r_y\vec j+\Delta r_z\vec k" contenteditable="false"><span></span><span></span></span><br><span class="equation-text" data-index="1" data-equation="\Delta r_x=x_B-x_A" contenteditable="false"><span></span><span></span></span><br><span class="equation-text" contenteditable="false" data-index="2" data-equation="\Delta r_y=y_B-y_A"><span></span><span></span></span><br><span class="equation-text" contenteditable="false" data-index="3" data-equation="\Delta r_z=z_B-z_A"><span></span><span></span></span>

<span class="equation-text" contenteditable="false" data-index="0" data-equation="\bar{\vec v} = \frac{\Delta \vec r}{\Delta t}"><span></span><span></span></span>

<span class="equation-text" contenteditable="false" data-index="0" data-equation="\vec v = \frac{d \vec r}{d t}"><span></span><span></span></span><br><span class="equation-text" data-index="1" data-equation="v_x = \frac{d x}{d t}" contenteditable="false"><span></span><span></span></span><br><span class="equation-text" data-index="2" data-equation="v_y = \frac{d y}{d t}" contenteditable="false"><span></span><span></span></span><br><span class="equation-text" data-index="3" data-equation="v_z = \frac{d z}{d t}" contenteditable="false"><span></span><span></span></span><br>