1 . 3 用图像表示物体的运动
我们可以用运动图像来形象表达物理规律,直观地描述物理过程,鲜明地反映物理量之间的关系.常见的运动图像有两种,一种是位移图像,即s—t 的函数图像,一种是速度图像,即v—t 的函数图像,从运动图像中我们可以得到物体运动的状态.
(1)位移图像(s—t 图像):
图像上一点切线的斜率表示该时刻所对应的速度;
图像是直线表示物体做匀速直线运动,图像是曲线则表示物体做变速运动;
图像与横轴交叉,表示物体从参考点的一边运动到另一边.
(2)速度图像(v—t 图像):
在速度图像中,可以读出物体在任何时刻的速度;
在速度图像中,物体在一段时间内的位移大小等于物体的速度图像与这段时间轴所围图形的面积的值;
在速度图像中,物体在任意时刻的加速度就是速度图像上所对应的点的切线的斜率;
图像与横轴交叉,表示物体运动的速度反向;
图像是直线表示物体做匀变速直线运动或匀速直线运动,图像是曲线表示物体做变加速运动.
Graphing the motion of objects gives us a way to interpret the motion that would otherwise be difficult.
Graphs will also allow you to show a large amount of information in a compact way.
Essentially you need to be able to sketch and interpret two main kinds of graphs in kinematics:
1.Displacement—Time Graphs
● Sometimes called s—t graphs, or position—time graphs.
2.Velocity—Time Graphs
● Sometimes called v—t graphs.
Displacement—Time Graphs
This type of graph is based on the most basic things we need to know about the motion of an object( position and time).
● Typically you will be given a table of values that show the displacement of the object over a particular period of time.
● If the graph shows complex motion (such as illustration below), you do not just draw a single best fit line. Instead, you need to look at each section of motion and determine what kind of line best fits the data.
● Don’t worry too much about sketching these complex situations …it is much more likely that you will draw an object moving in one way only.
● For the example graph shown in figure1.9, imagine that you are running in a marathon, and we have decided to graph your movement.
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