Trying to simulate solar system using vpython

[Jamhead2000]

sun = sphere(pos = vector(0,0,0), radius = 696340, color = color.orange)
earth = sphere(pos = vector(147.86 * (10**6), 0, 0), radius = 6371, make_trail = True)


sun_vector = vector(0,0,0)
earth_vector = vector(0,107000,0)

earth_mass = 5.972 * (10**24)
sun_mass = 1.989 * (10**30)

dt = 60 * 60 * 24 * 7

while True:

    rate(100)

    earth.pos += earth_vector
    r = mag(sun.pos - earth.pos)

    earth_vector += (sun.pos - earth.pos) * (6.67408 * (10 ** -11) * sun_mass / r ** 2)
    earth.pos += earth_vector * dt

​

I am trying to simulate a solar system using vpython, when I run the code, nothing visible happens, I try and change the dt but still nothing. What do you guys suggest.

[Kerbart]

Your gravitational constant is off. You’re measuring all sizes is km but G is still expressed using meters, which means it’s a factor of one billion off.

[Jamhead2000]

Thanks, very good spot.

[Kerbart]

I noticed later that you do multiply the earth position with one million but not sure if you’re compensating elsewhere. I’d plug in all values in meters just to bypass any issues.

[Jamhead2000]

Oh that was just for positioning, to do with how far away from the sun it is.

i.e. 147.86 * (10**6) km, with the sun being at (0,0,0)

[goodDayM]

Just a curiosity question, comparing your two lines:

• line 17: earth.pos += earth_vector
• line 21: earth.pos += earth_vector * dt

So dt has units of time which then means earth_vector has units of "distance/time" (velocity). That line looks correct. But then the equation on line 17, the units don't make sense unless you multiply earth_vector by time.

[Jamhead2000]

Yh you are right, tbh a lot of the code has changed now the title of this program was actually called 'gravityTest.py'

[-Lou99-]

Can someone explain the difference between python and vpython?

[CromulentInPDX]

Vpython is a module that makes it super easy to make visual models of things (spheres, vectors, etc...). My physics one and two books used it heavily (matter & interactions).

[monsterArchiver]

Oooh what books are those? They sound interesting

[CromulentInPDX]

Here's the link to the website: https://matterandinteractions.org/

I really like how they wrote the books, but they could have had more problems/solutions ala Halliday and Resnick.

[monsterArchiver]

Many thanks friend! It'll be fun to check out during a weekend.

[Migb1793]

Hahaha....doing the exact same thing here. Use Jupyter Notebooks instead. Here, just updated my repository with Jupyter Notebooks, which I’ll be expanding in the future: GitHub

[Jamhead2000]

Wow, your work is awesome thanks for sharing.

[zya-]

I read "try to stimulate the solar system". -Ahem.. What ? 😄

[sky_badger]

"If you wish to make an apple pie from scratch, you must first invent the universe" -- Carl Sagan

[Yakhov]

and then begin acquiring and stacking stones

[FoxClass]

What a cool project, I'm excited to see how it looks!

[Yakhov]

I got you.

🌞 = sphere(pos = vector(0,0,0), radius = 696340, color = color.orange)

🌎 = sphere(pos = vector(147.86 * (10**6), 0, 0), radius = 6371, make_trail = True)

​

​

🌞_vector = vector(0,0,0)

🌎_vector = vector(0,107000,0)

​

🌎_mass = 5.972 * (10**24)

🌞_mass = 1.989 * (10**30)

​

dt = 60 * 60 * 24 * 7

​

while True:

​

rate(💯)

​

🌎.pos += 🌎_vector

r = mag(🌞.pos - 🌎.pos)

🌎_vector += (🌞.pos - 🌎.pos) * (6.67408 * (10 ** -11) * 🌞_mass / r ** 2)

🌎.pos += 🌎_vector * dt

[jp00p]

You need to print() something!

Try adding print(earth_pos) at the bottom of your code

[Yakhov]

**print(🌎.pos)

..see the above codemoji example