# Do these cars rotate on themselves?

I was reading about the moon rotation around earth and the tidal lock related. I found some interesting information already here and on astronomy.stackexchange.com as well. The moon is known to have a full rotation period of ~27 days.

Let's consider these vehicles going around earth:

✓ They always "face" the same side to the earth

✓ They found themselves on the same position after a full revolution around earth

... but are they rotating on themselves and do they have this tidal lock effect? I would have said no but after reading about the tidal lock of the moon, should I say so? The same question can be asked for planes (if the fact that these cars touch the ground is an issue).

It is not the same as the tidal lock because the angular position of each car is determined by the reaction forces between their wheels and the surface of the planet, not by tidal forces which would tend to hold them at right angles to their depicted positions.

Tidal force pull along the line joining the two bodies and compress transverse to that line.

Yes, the buses are rotating as they drive around the earth. Think of looking at one of the buses from Polaris and you will see it rotate. It is not tidal lock that makes them rotate, it is geometry. If you go around something and keep the same side to it you will rotate. Tidal lock is what keeps one side of the moon facing earth, but there are other ways (like gravity and wheels here) to maintain that.

Yes, it is rotating, and yes it is the same as the tidal lock. The reason it is, is that you can decompose the motion into translational and rotational. Translational is what you do with your mouse: facing the same direction all the time. Conceptually after taken the transitional out, the motion left for the bus is rotational.

I have a counter example of what is NOT considered rotating: A kid circle around a table, while face north all the time.

After reading this and this very briefly I found out that there needs to be a significantly massive body with significant variation of gravity from the near to far end, that is a gravitation gradient, since such a gradient will not be present for a small aeroplane or a bus which is pretty much blown out of proportion in your picture, there should be no tidal locking.

If in some case, the objects in consideration are truly that big, then there must develop a tidal lock in due time, provided the body is not so formed that there is no net torque due to the gravitation gradient!