The part doesn’t move, but that doesn’t explain why all my velocity-based scripts are suddenly adding crazy amounts of force - especially considering I haven’t updated the game since the 1st of January.
Also, the rocket shown in the gif uses BodyForce to float and stuff, and after doing some more tests, it seems it’s mainly BodyForce and BodyGyro that has been “harmed”. BodyVelocity, BodyThrust and BodyPosition works like it used to.
This was enabled today:
Could it have to do with that?
I assume this is the problem. Guys, PGS = Default is the same as PGS = New right now. Default is no longer the same as Legacy.
Guys when you post bug reports please include links to the place and steps to reproduce.
Turns out it has to do with the new physical properties, yeah. I ran @NWSpacek’s command, and it works now. Thanks, and sorry for not realising this.
PGS ≠ physical properties:
PGS changes the math behind how physics are calculated.
Physical properties just adds density.
I had this issue and a lot of devs are currently, go to the workspace and set PhysicalPropertiesMode to legacy. This should fix all the unwanted ‘gravity’ behaviour
I’m not sure if PhysicalProperties will be forced anytime, but you could set the Density to whatever you want.
Does the PP.Density not affect Part:GetMass(), or did OP calculate the needed force once and stick with that value?
Density will change GetMass which is why we recommend using that function. Also, switching to legacy should only be considered a stop-gap measure if you need your game to work right now. The current plan is to actually phase out legacy as well, so you should not depend on it. Switch to legacy to give yourself time to tune the densities and forces, but don’t expect it to fix all your problems.
@ghostleader @Patrickblox @einsteinK
Bad bad bad bad advice to give. Legacy will be phased out in about a month. Please fix your scripts to properly ask the object about it’s mass before applying forces in Body Forces. The reason this is happening is because objects now have appropriate densities based on Material. These densities can be overwritten, see this thread for API details: LIVE - Upcoming Physical Properties and PartMaterial Changes
Please only use Legacy if the above advice doesn’t fix your game. If you have to use Legacy to fix your game PLEASE REPORT IT HERE, because LEGACY to me means “I could not make the game work correctly with variable mass/friction/elasticity values”.
Here is the migration announcement.
Please read this thread. For the last week if you opened Studio, there was a message directing you to that thread.
VERY IMPORTANT
Legacy is a temporary solution for you to migrate your game correctly. Please do not switch to legacy and expect EVERYTHING to be okay because LEGACY will be removed in about a month. Please fix your scripts to grab the correct mass values, or modify your objects to have the expected densities!
Um… didn’t Studio have a huge ass banner stating that this change will take place today…?
If that is the case, you’d better head over to the game creation forums on ROBLOX and tell people to NOT use legacy as that’s where I found the solution and it looks like a lot of people are using legacy.
It’s all well and dandy to ask us to script it but what about those who can’t script? We’re sitting ducks essentially 
(I would LOVE if someone could provide a script which gives us the same functionally as Legacy does currently)
You don’t need to know how to script. The UI is described in one of the threads I linked. If you set the Density to 1, things should behave mostly like Legacy.
Can you link me any of these threads?
If you aren’t using a script, how else will you set the density of parts to 1 en mass?
Select ALL the parts in the world using the “Explorer Filter” with they Keyword “Part”. Use the Studio UI.
I totally support converting places.
What bad advice did I give?
A month? Oh my I better inform my car maker friend he’s gonna be ticked! D:
2bad4him, I can’t wait! 
Sorry, I may have linked you because I wanted you to read the comments, not because I thought you were saying that people should just switch to Legacy.
I’ve added some scripts to the trouble-shooting section of the important public post:
