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Author Topic: Projectile Orbits and Satellite orbits  (Read 208505 times)
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Fu-Kwun Hwang
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1 Projectile Orbits and Satellite orbits
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on: January 29, 2004, 05:11:39 pm » posted from:,,Satellite Provider

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demo shown as Flash (5M byte)

 Newton had observed that any projectile launched horizontally is, in a sense, an Earth satellite.
 A rock thrown from a tall building sails in a modest orbit that soon intersects the earth not far from its point of launch.
 If the ball were fired more swiftly to start with, it would travel further. Futher increasing the speed would result in ever larger, rounder elliptical paths and more distant impact point. Finally, at one particular launch speed, the ball would glide out just above the planet's surface all the way around to the other side without ever striking the ground.
 At successively greater launch speeds, the ball would resolve in ever-increasing elliptical orbit until it moved so fast initally that it sailed off in an open parabolic or (if even faster) into a still flatter, hyperbolic orbit, never to come back to its starting point.
 This java applet let you change the launch speed by mouse click.
    click + to increase launch speed.
      click - to decrease launch speed.

Then Press Start to fire the ball.
 Press Reset to change parameters back to default values.
 The red arrow represents the velocity vector.
   Click the left mouse button near the tip of the
arrow and drag the mouse to change its velocity.
 Click right mouse button to stop the animation, press it again to resume.
   When will the ball start to go around without striking the ground?
   When will the motion become a circular motion? Enjoy it !
 Try to click the full checkbox, and find out what will happen.


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* earth.jpg (6.29 KB, 232x230 - viewed 1208 times.)

*** There are 1 more attached files. You need to login to acces it!
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Reply #1 on: January 30, 2004, 08:01:16 am » posted from:,,Satellite Provider

Subject: Orbit applet
Date: Fri, 30 Jan 1998 08:44:52 +0530
From: "Surendranath Reddy.B." <bsreddy@hd1.vsnl.net.in>
To: "Hwang" <hwang@phy03.phy.ntnu.edu.tw>
Dear Mr.Hwang,
I just saw your orbit applet. It was just the thing that I thought I would suggest to you.
Please consider the following suggestions.
Would it possible to show the initial position of the projectile,
its velocity and the angle the velocity makes with the line joining it and the center of the earth
and then give the option to launch.
The distance from the center of the earth could be made large ( twice, thrice.. the radius of the earth)
It would be better if the user gives these inputs by mouse clicks or by entering the values.
( It may be also a good idea to relate these values with (gr)^0.5,
the value required for a circular orbit. One could bring out the concept of escape velocity also.
Warm Regards
Surendranath Reddy.B.
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Reply #2 on: January 30, 2004, 08:01:45 am » posted from:,,Satellite Provider

Subject: Re:Suggestions
Date: Sat, 31 Jan 1998 11:41:23 -0500
From: "Pierce C. Barnard" <pbarnard@ultranet.com>
Organization: myself
To: hwang@phy03.phy.ntnu.edu.tw
Hi, I was examining your satellite & projectile motion applet and I found it to be very useful.
A suggestion, you may want to allow a user to set all paramters and
provide a button on the applet to start the applet.
This way the user will not have to keep on readjusting the applet while the projectile is in motion.
Pierce Barnard
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Reply #3 on: January 30, 2004, 11:50:08 am » posted from:,,Satellite Provider

Subject: Re: (no subject)
Date: Mon, 03 May 1999 18:44:25 +0200
From: Peter Brichzin <peter.brichzin@brasil.m.shuttle.de>
To: Fu-Kwun Hwang <hwang@phy03.phy.ntnu.edu.tw>
Hallo Mister Fu-Kwun Hwang,

thank you very much for sending all the files. To get a
good multimedia lesson is very important for me,
because it would be evaluated. A good evaluation will
give me a job es teacher.

I tried to understand your program. It's not easy
because my knowledge in Java is very basic. My problem
is now:
If I want to change the power of r in aceleration or
force F~ a ~ 1/r^2 to
F~ a ~ 1/r^x
then I have it to change in the method drivs of class
movingProjectile. (it works)
But this method never is called in whole
projectileOrbit.class. And to give a different exponent
to acceleration I have to give a argument to method
derivs (or are there other possibilities.

Is it possible that derivs is callt in rk4.
Could you send me please rk4.java or could you help me
in an other way with an idea to cahnge it.
Sorry that I ask you so much. Probably your time is
rare, but it would be a big help for me.
Thank you very much

Peter Brichzin

P.S: To get an imagination whatb I want I send you a
modified version: I added a Checkbox to change force.
But I can't get the connection between checkbos and
method derivs.
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Reply #4 on: March 26, 2004, 07:41:05 am »

Hi, My name Joe.

do you think i have a copy of your java codes because i am tryin to do a similar project. However, on a 2d map with some predicted satellite motion.

Please help me out.
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Reply #5 on: October 09, 2005, 08:10:15 pm »

Thank you very much for creating this applet and for sharing the files!

Chris D'Amato
Rutgers University
New Jersey, USA
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Chaitanya
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Reply #6 on: October 19, 2005, 08:07:41 pm »

hello,
your animations are inimitiable....can i have a java applete for it?....i really want it..i'm a physics student and i'm studying about kepler's planetry laws...it will be a great help if u send it to me...

urs thankfully

Chaitanya
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Fu-Kwun Hwang
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Reply #7 on: October 20, 2005, 11:24:28 am » posted from:Taipei,T'ai-pei,Taiwan

Just login to this forum and check out this wbe page again and click
the button "GET APPLET FILES" at the end of the first (applet) message.
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Reply #8 on: September 09, 2007, 09:57:30 pm »

Hello professor, can you explain the calculations or send me the source file ?

arthurprs1991@hotmail.com
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Fu-Kwun Hwang
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Reply #9 on: September 09, 2007, 11:41:50 pm »

The only equation used is F= -GMm/r2
I do not know what you would like me to explain?
Do you mean the numerical method? (I used Runge-Kutta 4th order method).
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arthurprs
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Reply #10 on: September 10, 2007, 06:28:01 am »

No angle work?
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Fu-Kwun Hwang
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Reply #11 on: September 10, 2007, 11:56:28 pm »

I do not understand what do you mean by "no angle work".
Would you please write it in more detail? I only can guest what do you mean. (It is not good)  Sad

If you keep click the + sign in the applet and let the velocity>=5812m/s.
The object will go around the earth and it would not fall on the earth.  Cheesy
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Reply #12 on: September 12, 2007, 09:19:01 am »

It means,
no cos and sin math to project G force to x and y axis ?
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Fu-Kwun Hwang
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Reply #13 on: September 12, 2007, 07:43:25 pm »

If you refer to the ejs code.
In the code, I calculate r=(x2+y2)1/2
,the force was calculated as F=-GMm/r2.
When I want to have x-component of the force: I use Fx=F*x/r
Similar for y-component of the force: Fy=F*y/r.
Because  x/r =cos(theta), y/r=sin(theta).
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Reply #14 on: September 13, 2007, 11:43:09 pm »

Tnx, thats it  Smiley

PS: if i could have professors like you  Huh
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Reply #15 on: December 02, 2007, 12:12:51 am »

A wonderful presentation that I just found while looking for information regarding the orbital patterns of satellites. I like to simplify things in order to make them easier to understand. Perhaps baseball serves as a simple example. The harder the ball is struck with the bat, the further it will travel. I am neither a physicist nor a mathematician. Heck I was even unable to upload my picture using the tools provided in your profile section. This is a wonderful site!
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Reply #16 on: December 02, 2007, 01:41:23 pm »

You can upload files(image/txt...files) if you click "Additional Options"(when you post/reply message).
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Reply #17 on: December 02, 2007, 10:29:29 pm »

Regarding the understanding of orbiting satellites, most are launched in an easterly direction and from the northern hemisphere. The orbital wave pattern centering on the equator varies according to the height of the orbit. Weather patterns also seem to follow a similar wave pattern as they move from west to east, but between the arctic circle and the tropic of cancer within the northern hemisphere. Such wave patterns seem to be in accordance with the physical nature of the earth's rotation.

Satellites in polar orbits seem to defy these physical laws. Could you explain more about such polar orbits? Also as a point of information, is it not physically possible for a satellite to be launched in a westerly direction? 

Post script, the picture I wanted to include is commonly called an avatar, and should have been allowed in the Profile set up tools, to show my picture as yours is shown beside each of your posts.
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Reply #18 on: December 03, 2007, 08:24:50 pm » posted from:Taipei,T\'ai-pei,Taiwan

Combined with the wave pattern of satellites orbit and earth's rotation so that satellite can cover more area on the earth to get more information.

You can launch a satellite in a westerly direction. But why you want to waste more energy? Because the earth's self rotation, the satellite have the same initial velocity as earth, so if it launch from west to east. You can save a lot of energy. Just like if you jumping from a car in the same direction as car, you will gain more energy!

Now, the server did not allow you to upload picture. But you can provide a URL of your picture (this should work).
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Reply #19 on: January 04, 2009, 12:41:26 am »

Hello, I'm making very similiar applet, but I'm little stuck. Can you please send me your java code. I will realy help me. Thank's a lot. JCH
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Reply #20 on: January 04, 2009, 02:40:41 pm »

Please check out the attachments under the first message.
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Reply #21 on: May 04, 2009, 08:04:50 pm » posted from:Padise,Harjumaa,Estonia

hello, so I have run into a little bit of trouble. I was creating newtons cannon in excel and it dose not work as supposed to. What happens is a very powerful slingshot effect. It will stay on orbit for a while, but eventually it will fly away.

my code looks like that. maa - earth ; kuul-bullet ; v-velocity
Because it is still in a test phase, I have left out some constants that do not change the orbits shape.

//setting centre
x0 = maa.Left + maa.Width / 2
y0 = maa.Top + maa.Height / 2
//mass
m = Sheets("nwkahur").Range("a2").Value
// input speed
vx = Sheets("nwkahur").Range("A1").Value
vy = 0

//movement
Do
x = x0 - kuul.Left + kuul.Width / 2
y = y0 - kuul.Top + kuul.Height / 2
r = (x ^ 2 + y ^ 2) ^ (1 / 2)

//new position

kuul.Left = kuul.Left + vx
kuul.Top = kuul.Top + vy
//new velocity
vx = vx + m / (r ^ 3) * x
vy = vy + m / (r ^ 3) * y

pause 0.0001

loop



I can understand that the problem is in calculations but, I cant but my finger on it. I would be very grateful, if you could help.


Kristjan Vilgo
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Reply #22 on: May 04, 2009, 09:17:05 pm » posted from:Taipei,T\'ai-pei,Taiwan

The Euler's method was used in your case to do the integration.
It only good for small time step and very far away case.
You need to use Runge-Kutta 4th order method to do the integration.
i.e. calculate v(t) from a(t).

You need to know numerical method or copy RK4 code from others to solve it correctly.
EJS is a tool for non-professional user who want to create simulation without much knowledge about numerical simulation.
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Reply #23 on: January 04, 2010, 03:25:35 pm » posted from:Colombo,Western,Sri Lanka

hello, so I have run into a little bit of trouble. I was creating newtons cannon in excel and it dose not work as supposed to. What happens is a very powerful slingshot effect. It will stay on orbit for a while, but eventually it will fly away.

my code looks like that. maa - earth ; kuul-bullet ; v-velocity
Because it is still in a test phase, I have left out some constants that do not change the orbits shape.

//setting centre
x0 = maa.Left + maa.Width / 2
y0 = maa.Top + maa.Height / 2
//mass
m = Sheets("nwkahur").Range("a2").Value
// input speed
vx = Sheets("nwkahur").Range("A1").Value
vy = 0

//movement
Do
x = x0 - kuul.Left + kuul.Width / 2
y = y0 - kuul.Top + kuul.Height / 2
r = (x ^ 2 + y ^ 2) ^ (1 / 2)

//new position

kuul.Left = kuul.Left + vx
kuul.Top = kuul.Top + vy
//new velocity
vx = vx + m / (r ^ 3) * x
vy = vy + m / (r ^ 3) * y

pause 0.0001

loop



I can understand that the problem is in calculations but, I cant but my finger on it. I would be very grateful, if you could help.


Kristjan Vilgo


I wrote  a similar code as urs and i think i am just as you stuck at the middle Smiley
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Reply #24 on: January 04, 2010, 09:30:08 pm » posted from:Taipei,T\'ai-pei,Taiwan

You can not use x(t+dt)= x(t)+vx(t) to calculate it.
vx=\frac{dx}{dt}=limit_{\Delta t\rightarrow 0} \frac{x(t+\Delta t)-x(t)}{\Delta t}

You can use x(t+dt)= x(t)+vx(t)*dt for very small value, otherwise you will get a very large error.

You need to learn some numerical method to calculate it.
Please check out Runge-Kutta 4th order method
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Reply #25 on: September 21, 2010, 03:13:22 pm » posted from:,,Taiwan

Here is an EJS version of the same applet.

Embed a running copy of this simulation

Embed a running copy link(show simulation in a popuped window)
Full screen applet or Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list
Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop. This work is licensed under a Creative Commons Attribution 2.5 Taiwan License
  • Please feel free to post your ideas about how to use the simulation for better teaching and learning.
  • Post questions to be asked to help students to think, to explore.
  • Upload worksheets as attached files to share with more users.
Let's work together. We can help more users understand physics conceptually and enjoy the fun of learning physics!
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Reply #26 on: September 21, 2010, 03:52:57 pm » posted from:SINGAPORE,SINGAPORE,SINGAPORE

nice Smiley
OSP has a version similar version by Todd Timberlake Newton’s Mountain Model http://www.compadre.org/osp/items/detail.cfm?ID=9391
This material is released under the Creative Commons Attribution 3.0.
each applet has their own strengths.  Grin
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Reply #27 on: November 19, 2010, 06:08:28 pm » posted from:Calcutta,West Bengal,India

After doing a bit of research i came to know that Newton was the first person to observe that any projectile launched horizontally is, in a sense, an Earth satellite. A rock thrown from a tall building sails in a modest orbit that soon intersects the earth not far from its point of launch.
-*-
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Reply #28 on: May 22, 2011, 10:09:16 pm »

Hi prof!

i tested the above JDK applet values against my new applet. http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=2204.0

the values are not the same.
could i check if your y value in thew above JDK applet is indeed 7.924E6 m

i suspect it is the same as counting from center of earth as 6.38E+7.924E6 = 1.43E07

which means if my understanding is valid, both applet did not give the same answer.



* calculationerror.png (141.59 KB, 658x608 - viewed 792 times.)

* calculationerror1.png (98.76 KB, 536x405 - viewed 829 times.)
« Last Edit: May 22, 2011, 10:11:13 pm by lookang » Logged
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