What is the best and/or correct way to propel something, like a bullet or a car?
I'm aware that one could use CFrame, and just loop an addition in the direction you want the object to go. You could also do a loop and change all the parts in the model's velocity. Or you could even use bodyForce's. However, I am unsure of the best one to use. I also think this would be a good question for everyone, not just me.

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Thank you greatly, plus body force's have a multitude of options. However, is this also the best "lag" resistant technique? I'm guessing it's mostly on the way I design the system.
If you're doing animations then use the animation plugin. I would reckon they know how to reduce lag with animations properly. If you're making a part that needs to be affected by physics(Like a ball or something) then use body forces, they shouldn't be lag inducing unless you do it to like many parts at once. Use streaming enabled to manage lag.