If a giant object would approach the Earth, would Earth start to turn faster or slower while the object starts to become nearer and nearer? I am asking myself this question: if a giant celestial object would approach the Earth, would Earth start to turn faster (then day duration would be diminished) or slower (day duration increased) while the object starts to become nearer and nearer?
Thank you!
Could be, you'd be better to ask this on the Physics site, by the way.

No, the spinning of a perfectly round object is not affected at all, it just keeps spinning identically.

Let's say ..



say another Sun appeared, just like that.

Yes, the path that Earth is taking would go crazy.  We might fly off, head towards this new Sun, starting making a figure of 8, or some crazy path!

But the spinning as such of the Earth would be totally unchanged.

The "way we point" ("North up" so to speak) would be completely unchanged, and the speed we turn at (ie, 24 hours a turn) would be unchanged.

This might seem surprising but, well, you can learn all about it in Newtonian physics!

Once again, no change to the spin as such of the Earth.  the "direction we point" (ie the axis we spin around) and the time taken is totally unchanged if (for some bizarre reason!) we are "moved around in the heavens".



Note that there would be some absolutely tiny effects due to things like relativity (have a read!), the water on our planet sloshing around, and after all our Moon could be moved, bashed, etc.  These effects on the speed we are spinning would be extremely small over the short period of time you're considering, in the "sci fi" scenario you outline, as seen in the diagram.