Gravitation between the Moon and the Earth: physics project

[isukatphysics69]

Is the force attracting the moon or pushing it away ?

The gravitational force is attracting the moon.. our position values are getting larger tho. we used eular integration, i was expecting the values to oscillate,
velocities here look really good tho imo. i still haven't quite made out what the position values are saying.

 

[BvU]

The gravitational force is attracting the moon..

So what about the sign of a ? If the moon leaves (R,0) with speed (0,vy) should ax and ay be > 0 ?

I'm surprised you introduce px and py if you already have a column x and y ?

(have to run: work!)

 

[isukatphysics69]

So what about the sign of a ? If the moon leaves (R,0) with speed (0,vy) should ax and ay be > 0 ?

I'm surprised you introduce px and py if you already have a column x and y ?

(have to run: work!)

ahh i see ok, have to fix that tommorow.

 

[isukatphysics69]

We screwed up our data, trying to fix. We changed the net force to a negative, not sure if everything updated

we have motion as px^2+py^2

i will close my eyes for a few minutes and then start from scratch i think starting from scratch will be a good idea but so tired

wait so the R is the sqrt(x^2 + y^2) since i have Earth centered at 0,0. so i needed the positions to calculate the acceleration with respect to time, but to get the positions i need the velocities, but in order to get the velocities i have to integrate the acceleration. this doesn't make sense. its like what came first, the egg or the chicked, well what do i need first, the position, but to get the position i need the velocity, but to get the velocity i have to integrate the acceleration. now i am confused after i thought i had it

oh wait i think it is because the velocity doesn't change it is always 1018 m/s lol.. i see nvm . i will close eyes for a few mins now then start from scratch.

when i went to graph my results the graph was not looking good. just two straight lines for the position. not sure how my professor got the circle. i used x^2+y^2 but the value was huge and didn't make sense.

 

[BvU]

i will close eyes for a few mins now then start from scratch.

Looks like you need some R&R ! (same as me, actually: 1:14 AM here and an early dentist appointment )
How did the exam go today ?

Never mind: the integration.

(added rows and columns so I can refer to them)

On line 1 there are the initial conditions 384000, 0, 0, 1018 for x, y, vx, vy.

From that you calculate (with formulas) r, theta, and a, ax, ay. (still on line 1).
​

On line 2 we are going to do our first integration step: from 0 to dt (I tried dt = 4000 sec here).

the new x is the x just above + vx * dt
the new y is the y just above + vy * dt
the new vx is the vx just above + ax * dt
the new vy is the vy just above + ay * dt
and the other ones you calculate

Or, in excel formulas:

Does that make sense to you ? If yes, then you can copy line 2 many times over
to see things go terribly wrong. We'll discuss that once you get the intgration going in a credible manner...

 

[isukatphysics69]

Looks like you need some R&R ! (same as me, actually: 1:14 AM here and an early dentist appointment )
How did the exam go today ?

Never mind: the integration.
View attachment 225349

(added rows and columns so I can refer to them)

On line 1 there are the initial conditions 384000, 0, 0, 1018 for x, y, vx, vy.

From that you calculate (with formulas) r, theta, and a, ax, ay. (still on line 1).
​

On line 2 we are going to do our first integration step: from 0 to dt (I tried dt = 4000 sec here).

​

Or, in excel formulas:

View attachment 225350

Does that make sense to you ? If yes, then you can copy line 2 many times over
to see things go terribly wrong. We'll discuss that once you get the intgration going in a credible manner...

Hi, the exam is tommorow and this is also due tommorow lol, ok i will be right back going to try to figure this out

 

[isukatphysics69]

Ok our dt is different but this is my redo of the data
here dt is 18000 seconds
i think this is looking pretty good here. i will check your post now 1 sec
my prof told me not to use trig functions so that is why i am using x/r and y/r

i can go back and change everything to 4000 seconds

 

[isukatphysics69]

 

[isukatphysics69]

 

[isukatphysics69]

Our acceleration components are looking a little different. i am refraining from trig functions because my prof advised against it.. i am trying to see if that is the only reason why
velocities differ slightly as well because of the acceleration difference, I'm pretty happy with what i am seeing right now

 

[isukatphysics69]

Looks like you need some R&R ! (same as me, actually: 1:14 AM here and an early dentist appointment )
How did the exam go today ?

Never mind: the integration.
View attachment 225349

(added rows and columns so I can refer to them)

On line 1 there are the initial conditions 384000, 0, 0, 1018 for x, y, vx, vy.

From that you calculate (with formulas) r, theta, and a, ax, ay. (still on line 1).
​

On line 2 we are going to do our first integration step: from 0 to dt (I tried dt = 4000 sec here).

​

Or, in excel formulas:

View attachment 225350

Does that make sense to you ? If yes, then you can copy line 2 many times over
to see things go terribly wrong. We'll discuss that once you get the intgration going in a credible manner...

Wait what do you mean?

 

[BvU]

Time step seems a bit big. Try 1000 --- however, I may have a bug in my stuff. ...

If the integration works and you make a scatter plot of y vs x, you should get something like a neat circle, at least initially.

prof advised against it

Prof is probably right (I can't get past x=0 without weird behaviour... (bug?)


I don't understand how you can go from x on first line to a bigger value if vx=0 ? And then on the next line to an even biger value when on line 2 vx < 0 ?

 

[isukatphysics69]

Time step seems a bit big. Try 1000 --- however, I may have a bug in my stuff. ...

If the integration works and you make a scatter plot of y vs x, you should get something like a neat circle, at least initially.

Prof is probably right (I can't get past x=0 without weird behaviour... (bug?)


I don't understand how you can go from x on first line to a bigger value if vx=0 ? And then on the next line to an even biger value when on line 2 vx < 0 ?

ohh yea i see that now.. this is where my initial confusion came in. i needed those position values to get the acceleration formulas R^2 values with respect to time.

Time step seems a bit big. Try 1000 --- however, I may have a bug in my stuff. ...

If the integration works and you make a scatter plot of y vs x, you should get something like a neat circle, at least initially.

Prof is probably right (I can't get past x=0 without weird behaviour... (bug?)


I don't understand how you can go from x on first line to a bigger value if vx=0 ? And then on the next line to an even biger value when on line 2 vx < 0 ?

I think i see the issue

 

[isukatphysics69]

So i had thought that i needed the positions with respect to time for the net force since the net force was (GMm)/(R²) and R= sqrt(px^2+py^2) since the Earth was fixed.
Edited
i will try to fix
think i see how to fix it

 

[isukatphysics69]

omg i am AN IDIOT

 

[isukatphysics69]

Omg i think its finally working i am so dumb i was changing the acceleration value now i am keeping "a" constant and only changing the ax and ay based on position currently dragging down 1 cell at a time since they all depend on each other

 

[isukatphysics69]

ok think i got it
now i have no idea how to graph this data, that's the next challenge

 

[isukatphysics69]

moon has escaped orbit

 

[isukatphysics69]

 

[isukatphysics69]

this is looking good to me, bvu thank you for all the help! i finally got it somewhat working
(the name "position y" is misleading) this is the x and y coordinates plotted

 

[isukatphysics69]

beautiful :')

 

[BvU]

In fact it shouldn't come out as a circle with the set of equations and initials we had. Has to do with reduced mass.

A physics complication. There's also a math complication: an issue with simple forward Euler for this kind of problem. But you learned a great deal which is far more important than getting the 'right' result.

Good luck with the test. I hope you did get some kip

 

[isukatphysics69]

In fact it shouldn't come out as a circle with the set of equations and initials we had. Has to do with reduced mass.

A physics complication. There's also a math complication: an issue with simple forward Euler for this kind of problem. But you learned a great deal which is far more important than getting the 'right' result.

Good luck with the test. I hope you did get some kip

Thank you, i will sleep after this report and study tommorow before the test, already went over the whole practice exam once

 

[BvU]

now i am keeping "a" constant and only changing the ax and ay based on position

Sorry for the bummer, but that isn't the idea of the exercise.

currently dragging down 1 cell at a time since they all depend on each other

in principle row n only depends on row n-1. That's forward Euler for you, the often self-quoted recipe$$x_n = x_{n-1} + v_{x, n-1} * dt \\y_n = y_{n-1} + v_{y, n-1} * dt \\v_{x, n} = v_{x, n} + a_{x, n-1} * dt \\v_{y, n} = v_{y, n-1} + a_{y, n-1} * dt$$

gotta face the drill now

 

[isukatphysics69]

Sorry for the bummer, but that isn't the idea of the exercise.
in principle row n only depends on row n-1. That's forward Euler for you, the often self-quoted recipe$$x_n = x_{n-1} + v_{x, n-1} * dt \\y_n = y_{n-1} + v_{y, n-1} * dt \\v_{x, n} = v_{x, n} + a_{x, n-1} * dt \\v_{y, n} = v_{y, n-1} + a_{y, n-1} * dt$$

gotta face the drill now

aw crap what
its not possible at this point, its 4 am and due tommorow

 

[isukatphysics69]

aw crap what
its not possible at this point, its 4 am and due tommorow

 

[isukatphysics69]

i am attempting to fix it

 

[isukatphysics69]

i think i just fixed it, if you come back please let me know
oh my lord i think i may have just fixed it

 

[isukatphysics69]

 

[isukatphysics69]

Graphs are updated and still looking good, not much of a change in the graphs as i go lower the acceleration is decreasing

 

[isukatphysics69]

 

[isukatphysics69]

I think this is what i have to go with regardless. i gave it my best shot now have to move on and will read feedback if given from prof

 

[isukatphysics69]

this is screwed

 

[BvU]

Kudos for your tenacity ! Hope the test went well...

I mentioned you in a related thread . A lot of good reading in the pdf link in post #5.

There also is a recent earth-moon thread here:

So I was messing with VPython, trying to create an Earth-Moon System. I got the actual gravity to work, and can create some nice ellipical orbits. However I run into trouble trying to make the actual (almost) circular orbit of the moon.
...

 

[isukatphysics69]

Definitely failed that final exam but my test average this semester was 84 over 6 test so I think I will pass the course. Very disappointed in self but how on Earth ani supposed to pass a final that has 2/6 questions that we covered last week. So I answers 3/ 6 questions and we were supposed to answer 4/6 to have a chance at full credit plus this project lack of sleep and food was a recipe for disaster plus I'm just a complete moron but whatever I failed sometimes you fail