(共25张PPT)
简谐运动
第十一章 机械振动
从运动学的角度定义简谐运动
1.学生对各种类别运动的认识
●先认识运动学特点
●再了解动力学条件
2.新教材关于简谐运动定义的教学线索
定性描述振动
介绍弹簧振子
实验作出弹簧振子的位移－时间图象
分析弹簧振子的位移－时间图象是正弦曲线
定义简谐运动
科学漫步：匀速圆周运动质点投影的运动是简谐运动
加速度大小方向都不变的匀变速直线运动。（自由落体运动）
思考1：我们以前学过哪些运动形式？
加速度大小方向都不变的匀变速曲线运动。（平抛运动）
加速度大小不变方向改变的变加速曲线运动。（匀速圆周运动）
思考2：如果加速度大小和方向都改变，那么物体会做什么运动呢？
观察
物体在平衡位置附近所做的往复运动叫做机械振动，简称振动。
一、机械振动
（1）、围绕着“中心”位置
（2）、“往复”运动
这些运动的共同特点是什么？
小球和弹簧所组成的系统称作弹簧振子，有时也把这样的小球称做弹簧振子或简称振子。
2、理性化模型：
（1）不计阻力
（2）弹簧的质量与小球相比可以忽略。
1、概念：
二、弹簧振子——理想化模型
O
二、弹簧振子——理想化模型
思考：振子的运动是怎样一种运动呢？
振子的位移x都是相对于平衡位置的位移，以平衡位置为坐标原点O，沿振动方向建立坐标轴。规定在O点右边时位移为正，在左边时位移为负。
三、弹簧振子的位移—时间图象
O
研究弹簧振子的运动
（1）、频闪照相
图像绘制方法
三、弹簧振子的位移—时间图象
思考：如何理解这就是振子的位移时间图象
也可以用数码照相机拍摄竖直方向弹簧振子的运动录像，得到分帧照片，依次排列得到图象。
做一做
（2）、用运动传感器测量垂直悬挂弹簧振子的运动
三、弹簧振子的位移—时间图象
三、弹簧振子的位移—时间图象
也可用位移传感器和计算机描绘
在弹簧振子的小球上安装一枝绘图笔，让一条纸带在与小球振动方向垂直的方向上匀速运动，笔在纸带上画出的就是小球的振动图象。
(3)、描图记录法
二、弹簧振子的位移—时间图象
多媒体实验室
体验：
一同学匀速拉动一张白纸，另一同学沿与纸运动方向相垂直方向用笔往复画线段，观察得到的图象
三、弹簧振子的位移—时间图象
这种记录振动的方法在实际中有很多应用。医院里的心电图及地震仪中绘制的地震曲线等，都是用类似的方法记录振动情况的。
绘制地震曲线的装置
心电图
拓展 旋 转 矢 量
动画演示：简谐与圆周运动等效
用旋转矢量图画简谐运动的 图
二、弹簧振子的位移—时间图象
1、定义：如果质点的位移与时间的关系遵从正弦函数的规律，即它的振动图象（x—t图象）是一条正弦曲线，这样的振动叫做简谐运动。简谐运动是最简单、最基本的运动。例如：弹簧振子的运动就是简谐运动。
三、简谐运动及其图象
2、简谐运动的图象
t
x
o
关于简谐运动下列说法正确的是（ ）
A、简谐运动一定是水平方向的运动
B、所有的振动都可以看成简谐运动
课 堂 练 习
C、物体做简谐运动时的运动轨迹一定是正弦曲线
D、只要振动图象是正弦曲线,物体一定做简谐运动
D
某一弹簧振子的振动图象如图所示，则由图象判断下列说法正确的是（ ）
A、振子偏离平衡位置的最大距离为10cm
B、1s到2s的时间内振子向平衡位置运动
C、2s时和3s时振子的位移相等，运动方向也相同
D、振子在2s内完成一次往复性运动
10
5
0
-5
-10
t/s
x/cm
1 2 3 4 5 6
AB
课 堂 练 习
20
-20
t/s
x/cm
0 1 2 3 4 5 6 7
D
课 堂 练 习
某弹簧振子的振动图象如图所示，根据图象判断。下列说法正确的是（ ）
A、第1s内振子相对于平衡位置的位移与速度方向相反
B、第2s末振子相对于平衡位置的位移为-20cm
C、第2s末和第3s末振子相对于平衡位置的位移均相同，但瞬时速度方向相反
D、第1s内和第2s内振子相对于平衡位置的位移方向相同，瞬时速度方向相反。
t/s
O
3
-3
8
16
x/m
1、质点离开平衡位置的最大位移？
2、1s末、4s末、10s末质点位置在哪里？
3、1s末、6s末质点朝哪个方向运动？
课 堂 练 习
4、质点在6s末、14s末的位移是多少？
5、质点在4s、16s内通过的路程分别是多少？
小 结
1、机械振动：物体在平衡位置（中心位置）两侧附近所做往复运动。通常简称为振动。
平衡位置：振子原来静止时的位置
2、弹簧振子理性化模型：不计阻力、弹簧的质量与小球相比可以忽略。
3、简谐运动：质点的位移与时间的关系遵从正弦函数的规律，即它的振动图象（x—t图象）是一条正弦曲线。
t
x
oFileIO Xtra
Version 1.0.4 - 09dec97 CH
FileIO Xtra for Macromedia Director 6.0
=======================================
FileIO provides a set of methods allowing users of Macromedia Director 6.0 to
programmatically access files using the Lingo scripting language. The FileIO
Xtra is a scripting Xtra. The scripting Xtra interface is portable across
all Macromedia products. Hence the FileIO Xtra may be used with Authorware 4.
Using FileIO
============
If automatic opening is desired, place a copy of the FileIO Xtra for your platform
into Application Xtra's folder. If automatic opening is not desired, the Xtra can be
placed anywhere and opened using Lingo's 'openXLib' command. This applies to
projector's as well, the Xtra must be placed in an Xtra's folder in the same folder
as the projector.
Each instance of FileIO can reference a single open file. If multiple files are to
be opened simultaneously, a new instance of FileIO is required for each opened file.
A single instance can be used to open multiple files, as long as the file is closed
before a new file is opened. To create a new instance, use the new() method, defined
below. To dispose of an instance, set the instance variable to 0. All methods that
read from or write to the file must be called after the file has been opened using
the openFile() method. If a new file is to be opened using the same instance, the
file must be closed using closeFile(). Files can be opened in three different modes:
Read, Write and Read/Write. When writing to a file, the contents of the file after
the current position are overwritten.
Example Lingo
set myFile = new(xtra "fileio") -- Create an instance of FileIO
set fileName = displayOpen(myFile) -- Display Open Dialog and return the fileName
openFile(myFile, fileName, 1) -- Open the file
set theFile = readFile(myFile) -- Read the file and return a string to Lingo
closeFile(myFile) -- Close the file
set myFile = 0 -- Dispose of the instance
In this example, we created a new instance and stored it in the variable myFile.
Next, the displayOpen() method is used to display an open dialog to allow a file to
be chosen. The file is returned as a fully-qualified path string to Lingo. The file
is then opened in read only mode, the contents of the file are read, and the file is
closed. Lastly, the instance is disposed of.
Known Problems
==============
The createFile() method does not support relative filenames, or the Lingo '@'
operator in pathnames. This will be fixed in a later version.
The displaySave() method does not directly inform Lingo whether a user is
replacing an existing file. The workaround is to attempt to create the file using
createFile() and check the error code for a "File Already Exists" error.
History
=======
09dec97 (v1.0.4)
Fixed a problem leading to garbage characters appearing at the ends of lines,
or possibly crash.
18apr97 (v1.0.2)
Fixed parenting problem with displaySave() and displayOpen() methods.
Added support for Authorware.
27may96 (v1.0.1)
Added support for double-byte character sets.
Added version() method to report FileIO Xtra version information.
Added getOSDir() to return a full path to the Windows Directory/System Folder.
15mar96 (v1.0.0 Beta)
First public release.
Method Reference
================
The first line of each definition contains the method name, a list of parameters and
thier value types. The internal name of the FileIO Xtra is "fileio". This name is
used whenever referencing the xtra using the form 'xtra "fileio"'.
Note that while Director and projector's can use net-based files by supplying a URL
for a filename, the FileIO Xtra cannot. It is limited to accessesing files available
via filesystems mounted on the local system.
New methods will appear at the bottom of this list.
---
mMessageList( xtra reference )
Returns a list of methods and parameters, as well as a brief explanation of each.
---
new( xtra reference )
This is called to create a new instance of FileIO. The Xtra can be referenced by name
or number. It returns an instance variable used to reference the instance.
---
fileName( instance )
Returns the fileName string of the current open file. The file must be open use this
method.
---
status( instance )
Returns the error code returned by the last method called. The value is returned as
an integer.
---
error( instance, int error )
Returns a readable error string. A numeric error code is passed in as the
second argument. The errors returned can be any of the following:
"OK"
"Memory allocation failure"
"File directory full"
"Volume full"
"Volume not found"
"I/O Error"
"Bad file name"
"File not open"
"Too many files open"
"File not found"
"No such drive"
"No disk in drive"
"Directory not found"
"Instance has an open file"
"File already exists"
"File is opened read-only"
"File is opened write-only"
"Unknown error"
---
setFilterMask( instance, string mask )
Sets the filter mask used by calls to displayOpen() and displaySave(). The filter
mask determines what files to show when displaying an Open or Save dialog. The second
parameter is a string representing the filter mask to set. On Windows, this is a
comma seperated string of file types and associated extensions (e.g. "All
Files,*.*,Text Files,*.TXT"), and a string of types on the Macintosh (e.g.
"TEXTPICT"). On Windows, the filter mask string is limited to 256 characters. On the
Macintosh, you are limited to four four-character types. When a new instance of
FileIO is created, the filter masks defaults to all files. To reset the filter mask to
display all files after it has been set, just pass in an empty string (e.g.
setFilterMask(me, "")).
---
openFile( instance, string fileName, int openMode )
Opens the named file. This call must be used before any read/write operations can
take place. The filename can be either a fully-qualified path and filename, or a
relative filename. The Lingo '@' pathname operator is supported. The openMode
parameter specifies whether to open the file in Read, Write or ReadWrite mode. Valid
Flags are: 0 Read/Write, 1 Read, 2 Write.
---
closeFile( instance )
Closes a file that has been previously opened using the openFile() method.
---
displayOpen( instance )
Displays a platform specific Open dialog allowing a user to specify a file. Returns a
fully-qualified path and fileName to Lingo. The setFilterMask() method can be used to
control what file types are displayed in the dialog.
---
displaySave( instance, string title, string defaultFileName )
Displays a platform specific Save dialog allowing a user to specify a file. Returns a
fully-qualified path and fileName to Lingo. The setFilterMask() method can be used to
control what file types are displayed in the dialog. The string and defaultFileName
parameters allow you to specifiy a default filename to be displayed, as well as title
text for the save dialog.
---
createFile( instance, string fileName )
Creates a file. The fileName must be either a fileName to be created in the current
directory, or a fully-qualified path and fileName. The Lingo '@' pathname operator
and relative paths are not supported. After creating the new file, the file must be
opened before it can be written to.
---
setPosition( instance, position )
Sets the file position of the current open file. The file must be open to use this
method.
---
getPosition( instance )
Gets the file position of the current open file. Returned as an integer. The file
must be open to use this method.
---
getLength( instance )
Gets the length of the currently opened file. Returned as an integer. The file must
be open use this method. The value returned is the length of the file in bytes.
---
writeChar( instance, string theChar )
Writes a single character to the file at the current position. The file must be open
in write or read/write mode to use this method.
---
writeString( instance, string theString )
Writes a string to the file at the current position. The file must be open in write
or read/write mode to use this method.
---
readChar( instance )
Reads the character (either single or double-byte) at the current position and then
increments the position. The character is returned to Lingo as a string. The file must
be open in read or read/write mode to use this method.
---
readLine( instance )
Reads from the current position up to and including the next CR, increments the
position, and returns the string to Lingo. The file must be open in read or
read/write mode to use this method.
---
readFile( instance )
Reads from the current position to the end of the file and returns the file to Lingo
as a string. The file must be open in read or read/write mode to use this method.
---
readWord( instance )
Reads the next word starting at the current position. The file must be open in read
or read/write mode to use this method.
---
readToken( instance, string skipChar, string breakChar )
Reads the next 'token' starting at the current position. Characters matching the
skipChar parameter are "skipped" and the file is read until breakChar is encountered.
The file must be open in read or read/write mode to use this method. This method will
read double-byte tokens as long as the skip and break are single-byte characters. It
will not detect double-byte skip or break characters.
---
getFinderInfo( instance )
Returns the Type and Creator of the current file as a string. This method does
nothing when used under Windows. The file must be open to use this method.
---
setFinderInfo( instance, string typeAndCreator )
Sets the Type and Creator of the current file. The string takes the form of a space
seperated set of TYPE and CREATOR codes (e.g. "TEXT TTXT"). This method does nothing
when used under Windows. The file must be open to use this method.
---
delete( instance )
Deletes the currently opened file. The file must be open use this method.
---
version( xtraRef )
Returns FileIO version and build information. Useful when filing
bug reports, determining installed version while authoring, etc. No practical use beyond this.
---
getOSDir( )
Global method that returns the full path to either the Windows directory, or the System Folder
depending on which OS is currently being used. Does not require a child instance or
Xtra reference to call.
---
