# Marble slides problems
**URL:** https://cl.desmos.com/t/marble-slides-problems/1090
**Category:** Questions
**Created:** [May 28, 2020, 10:45pm UTC](https://cl.desmos.com/t/marble-slides-problems/1090 "2020-05-28T22:45:09Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Roger](https://cl.desmos.com/u/Roger)
#### Post date: [May 28, 2020, 10:45pm UTC](https://cl.desmos.com/t/marble-slides-problems/1090/1 "2020-05-28T22:45:09Z")
Hi !
I am trying to make this marble slides work but I don’t understand why sometimes the balls fall both sides but not always. It frustrates me!
> **[Marble slides Ellipses • Activity Builder by Desmos](https://teacher.desmos.com/activitybuilder/custom/5b0dc988ce1fd861d5471d02)**
>
> Ellipses Marble slides. Pre-calculus.
>
> This activity is made with love for the College Algebra students and for Angel Bahena (Algebra 2) of Kelvyn Park High School of Chicago.
>
> From Roger Borrell
Thank you
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### Author:  [@cwinske](https://cl.desmos.com/u/cwinske)
#### Post date: [May 31, 2020, 12:51pm UTC](https://cl.desmos.com/t/marble-slides-problems/1090/2 "2020-05-31T12:51:05Z")
I believe the balls follow a bit of physics with a a little bit of randomness.
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### Author:  [@sergeballif](https://cl.desmos.com/u/sergeballif)
#### Post date: [June 2, 2020, 10:35pm UTC](https://cl.desmos.com/t/marble-slides-problems/1090/3 "2020-06-02T22:35:07Z")
I seem to recall that @denis once mentioned that the viewport size or resolution could make a difference in some instances (which makes it very hard to verify reports of problems). The marbleslide physics make use of an external tool (box2d?) that sometimes doesn’t play as nicely as we would like. You are not alone in feeling frustrated about inconsistent behavior. Thankfully, the glitches are fairly rare.