Welcome, Guest

Author Topic: [BUG] Planet Rotational Periods.  (Read 2252 times)

codefantastic

  • *****
  • Posts: 175
  • I hope these asteroids don't cause trouble
[BUG] Planet Rotational Periods.
« on: September 23, 2015, 05:42:53 AM »
I assume this is just a bug but, when I spawn planets (or any object really), their rotational periods seem odd. For example, usually they will spawn with a rotational period of around 200 days, but I have, on several occasions, spawned planets with rotational periods of 1 million years (that's cray cray). As for as I know, rotational period is based of size, density, and composition of an object, so I don't know if these numbers are accurate.

codefantastic

  • *****
  • Posts: 175
  • I hope these asteroids don't cause trouble
Re: [BUG] Planet Rotational Periods.
« Reply #1 on: September 23, 2015, 05:57:56 AM »
I should actually put this in the support/bug reporting forum :P

Arian

  • *****
  • Posts: 87
Re: [BUG] Planet Rotational Periods.
« Reply #2 on: September 23, 2015, 10:02:02 AM »
As for as I know, rotational period is based of size, density, and composition of an object, so I don't know if these numbers are accurate.
Actually these factors play a rather limited role there. Any object can and will have an individual rotation period caused for the biggest part by external means. Collisions in general are the main reasons for individual rotation periods, starting with collisions within the accretion disk. But also the orbits of bodies within the accretion disk has its part in that. They define the initial direction of the rotation.
Collisions between planets or planets and large enough bodies can speed up or slow down rotation and heterogeneous density (mass distribution) along with gravity effects of passing by bodies do their share too. To the extent that actual binary planets are believed to get tidally locked eventually because their heavier sides would constantly attract each other the most. I'm not quite sure whether that is always true because different rotation periods of binary planets could as well have speed up effects and cause the rotations of both planets to change in apparently chaotic ways.

In US2 the rotation period changes with mass, size and density changes because these three are interconnected, but not so the rotation speed. If the rotation speed stays the same on an object with decreasing radius however, the rotation period has to increase, since a point at the equator has to move a shorter distance to get around the axis as the planet becomes smaller. Moving at 1,674.4 km/h gets you faster around a circumference of say 40,075 km than around one of 80,000km after all.

Dan Dixon

  • Creator of Universe Sandbox
  • Developer
  • *****
  • Posts: 3243
    • Personal Site
Re: [BUG] Planet Rotational Periods.
« Reply #3 on: September 23, 2015, 10:06:59 PM »
Are you talking about how fast the body spins?

A really spin could take 1 million years...

And I'm pretty sure that we're just randomizing that value... I don't think it's based on other factors like you're suggesting.

gabriel.dac

  • *****
  • Posts: 517
  • Brazillian dude
Re: [BUG] Planet Rotational Periods.
« Reply #4 on: September 24, 2015, 04:20:40 AM »
What does size, density and materials have to do with how fast anything spins?
« Last Edit: September 24, 2015, 03:21:22 PM by Dan Dixon »

Greenleaf

  • Thomas Grønneløv
  • Development Team
  • *****
  • Posts: 211
Re: [BUG] Planet Rotational Periods.
« Reply #5 on: September 24, 2015, 05:03:50 AM »
What does size, density and materials have to do with how fast anything spins?


Assuming all bodies get random angular momentum from the same distribution, larger heavy objects would spin slower than small small light ones.



« Last Edit: September 24, 2015, 03:21:29 PM by Dan Dixon »

Arian

  • *****
  • Posts: 87
Re: [BUG] Planet Rotational Periods.
« Reply #6 on: September 24, 2015, 11:50:34 AM »
What the hell does size, density and materials have to do with how fast anything spins?

Well, put on your ice skaters and do some pirouettes on ice. Stretch your arms away from your body and then wrap them around your chest.
Repeat that with a bowling ball in one hand and again with a bowling ball in each hand.

Basically those things influence the rotation speed indirectly because gravity and conservation of momentum interact with/depend on those factors. They don't determine the spinning speed but they determine the amount and direction of energy needed to change it since they will provide for a countering or supporting force depending on the direction of force working on the spinning object (e.g. a colliding body).