必修2第5章第7节向心力课件:15张PPT

FileIO
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.
---(共15张PPT)
所受合外力__________零
【复习】
◆
什么是匀速圆周运动？
◆
“匀速”的含义是什么？
匀速圆周运动是___速曲线运动
变
运动状态改变
一定不等于
一定具有______。
加速度
◇
加速度上节课我们已经做过讨论
◇
而物体所受的合外力有何特点？
感受向心力
看看
想想
◆牵绳的手有什么感觉？
◆如果松手，将会发
生什么现象？
受到一个拉力的作用，
且力的方向____变化
不断
例：用手抡一个被绳系着的物体
在水平面上做匀速圆周运动
沿切线方向飞出去
1、向心力定义：
　　做匀速圆周运动的物体所受到的指向圆心的合外力。
2、公式：
②向心力的作用：
　　　　　　　只改变线速度的方向
①方向时刻发生变化（始终指向圆心且与速度方向
垂直）
③向心力是根据力的作用效果来命名的，它不是具
有确定性质的某种力。可以是某一个力，也可以是几个力的合力所提供。
一、向心力
3、特点：
实验：用圆锥摆粗略验证向心力的表达式
mg
T
F
法二：小球受力
θ
L
r
法一：用天平测出小球的质量m，
用秒表测出转n圈的时间t
tanθ=
r
/
h
O’
O
h
〖做一做〗
阅读课本
感受：向心力的大小与
、
、
的关系
质
量
半
径
角速度
实验：用手抡沙袋
实验方法：
控制变量法
m、ω不变，r越大，F越____
m、r不变，ω越大，F越____
r、ω不变，m越大，F越____
大
大
大
O
G
N
F
小球受力分析：
O
N与G相平衡，所以合力为F
O
F
F
F
V
V
V
O
结论：向心力是小球所受的合力，且与
垂直
速度
V
图2
例：下列物体做匀速圆周运动时，向心力分别由什么力提供？
①人造地球卫星绕地球运动时；
万有引力
②小球在光滑的水平桌面上运动；(如图1)
③小球在水平面内运动；(如图2)
图1
细绳的拉力
小球重力和绳拉力的合力
例：下列物体做匀速圆周运动时，向心力分别由什么力提供？
④玻璃球沿碗(透明)的内壁在水平面内运动；(如图3)(不计摩擦)
⑤使转台匀速转动，转台上的物体也随之做匀速圆周运动，转台与物体间没有相对滑动。(如图4)
图3
图4
小球重力和内壁支持力的合力
台面的静摩擦力
二、变速圆周运动和一般曲线运动
1、变速圆周运动：
2、一般的曲线运动
Ft
0
F
Fn
总结：切向分力改变速度的大小，法向分力改变速度的方向
处理方法：把曲线分割成许多短的小段，每一
段都看作一小段圆弧，对圆弧采用圆周运动的方法分析
小
结
一、向心力
1、定义
2、表达式
3、特点
二、变速圆周运动和一般曲线运动
例1：A、B两球都做匀速圆周运动，A球质量为B球的3倍，A球在半径25cm的圆周上运动，B球在半径16cm的圆周上运动，A球转速为30r/min，B球转速为75r/min，求A球所受向心力与B球所受向心力之比。
解：
例2：一物体在水平面内沿半径
R=20
cm的圆形轨道做匀速圆周运动，线速度V=0.2m/s，那么，它的向心加速度为______m/s2，它的角速度为_______rad/s，它的周期为______s
0.2
1
2π
例3：如图所示，将一单摆拉到摆线呈水平位置后由静止释放，在P点有钉子阻止OP部分的细线移动，当单摆运动到此位置受阻时
A．摆球的线速度突然增大
B．摆球的角速度突然增大
C．摆球的向心加速度突然增大
D．摆线的张力突然增大
BCD
1、在水平湿滑的道路上转弯时，无论是骑车还是驾车，都要减速行使，为什么？
2、在高速公路和铁轨的弯道处，路基都要设计成倾斜的，为什么？
思考下列的问题：