Gravitational acceleration calculation

None · 2022-08-10T15:36:27

I'm getting strange results when calculating the physics between two objects. My goal is to build a galaxy simulator that can simulate how galaxies consisting of 100s of stars might look when interacting. It's a fun little side project and I'm not even sure how it'll turn out (which is part of the fun). I have a really limited background in math and physics so this is a pretty big challenge for me atm. I'm starting with one star and a static object to attract it to nail down the basic physics. The problem I'm facing is that, as star one approaches the static object it's is accelerating as expected and when it passes the object I expect the velocity to slowly bleed to zero and the star to fall back in. However, after passing the static object the star is behaving oddly. Depending on my delta time variable It position sometimes shoots off crazy fast in one direction or another. I'm too new to all of this and there are too many variables for me to follow where exactly the issue lies. As an FYI this is a little web app written in javascript and not an actual video game. However, the concepts are similar to calculating video game physics and most web developer forums aren't helpful. Here is a link to the code in codepen. NOTE: If the “try me” button doesn't appear try shrinking your browser down in size or scrolling down to find the button. Finally, the rendering engine (canvas) doesn't appear to be the problem as I can see the issue in the console as being related to the calculations and not he rendering. let frameCount = 0; let stars; let dt; let gravConst = 6.674 * Math.pow(10, -11); // let solarMass = Math.pow(10, 30); // let lightYear = 9.5 * Math.pow(10, 15); let solarMass = 1; let lightYear = 1; let yearCounter; stars = [ { x: 250, y: 75, m: 1, v: 0 }, { x: 275, y: 75, m: 1, v: 0 } ]; dt = 50000; yearCounter = 0; const render = () => { let canvas = document.getElementById("canvasRef"); const context = canvas.getContext("2d"); let animationFrameId; frameCount++; animationFrameId = window.requestAnimationFrame(render); draw(context, frameCount); }; const draw = (ctx, frameCount) => { // console.log(frameCount) ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height); ctx.fillStyle = "#ffffff"; calculateGravAccel(stars[0], stars); drawStar(stars, ctx); }; let calculateGravAccel = (star, stars) => { // Force on current star by all other star sources (newtons) let m1 = stars[0].m * solarMass; let m2 = stars[1].m * solarMass; let distance = (stars[0].x - stars[1].x) * lightYear; let xDistance = stars[0].x - stars[1].x; let f = gravConst * (m1 * m2) / Math.pow(distance, 2); console.log(f); // Convert velocity to account for the fact that the force is now coming from behind // New velocity of current star star.v = distance < 0 ? star.v + (f / m1) * dt : star.v - (f / m1) * dt; // Position star.x = star.x + star.v * dt; // Ellapsed Time yearCounter += dt; }; const drawStar = (stars, ctx) => { console.log(`x:${stars[0].x} y: ${stars[0].y} v: ${stars[0].v}`); ctx.beginPath(); ctx.arc(stars[0].x, stars[0].y, 5, 0, 2 * Math.PI); ctx.arc(stars[1].x, stars[1].y, 5, 0, 2 * Math.PI); ctx.fill(); };

Math and Physics Programming gravity

Started by jonny-b May 10, 2022 05:04 PM

143 comments, last by taby 2 years, 5 months ago

JoeJ

4,405

July 15, 2022 07:10 AM

I understood it well enough at least to guess the file name is probably a bug. : )

jonny-b

Author

July 15, 2022 02:43 PM

@taby Reading it now. This is way over my head though. I can check for typos though, lol. One thing might be your reference to assembly programmers. If this is meant for astrophysicists they may be unfamiliar with assembly languages. It might be worth adding just another sentence of detail to prevent confusion.

None

jonny-b

Author

July 15, 2022 02:59 PM

Also, regarding this line

Thus, all of physics is about processes and computation

This statement would assume the universe has a processing speed / frame rate, correct? Since our current physics break at Planck time would you conclusion require new physics?

https://astronomy.swin.edu.au/cosmos/p/Planck+Time#:~:text=The%20Planck%20time%20is%20the%20time%20it%20takes%20for%20a,which%20current%20physical%20theories%20fail.

None

taby

1,557

July 15, 2022 03:40 PM

JoeJ said:
I understood it well enough at least to guess the file name is probably a bug. : )

LOL yeah, I just copy and pasted the files from another paper and edited that. ?

taby

1,557

July 15, 2022 03:41 PM

jonny-b said:
Also, regarding this line
Thus, all of physics is about processes and computation
This statement would assume the universe has a processing speed / frame rate, correct? Since our current physics break at Planck time would you conclusion require new physics?
https://astronomy.swin.edu.au/cosmos/p/Planck+Time#:~:text=The%20Planck%20time%20is%20the%20time%20it%20takes%20for%20a,which%20current%20physical%20theories%20fail.

I"m hesitant to say that there is a minimum time slice. Time is not necessarily quantized.

jonny-b

Author

July 15, 2022 03:45 PM

@taby , So where/when would these processes occur and how could one be interrupted?

None

taby

1,557

July 15, 2022 07:11 PM

everything is a process, or sub-process.

the source of time dilation are force-carrying particles, like the graviton or the photon

taby

1,557

July 15, 2022 07:12 PM

Are you familiar with Einstein’s Light Clock gizmo?

taby

1,557

July 15, 2022 07:22 PM

P.S. The reference to the assembly language is basically me being compliant. I was told that the paper needed to be related to computer science, so there we have it.

taby

1,557

July 16, 2022 04:41 AM

I edited the whole paper. I added a reference to Abrash's book re: assembly programming. ?

Gravitational acceleration calculation

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Gravitational acceleration calculation

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