Does the earth translate around the sun?

[nonequilibrium]

(imagining a perfect Earth without rotation around its own axis etc)

In which way does it; and which way doesn't it?

 

[Jack21222]

Maybe I'm the moron here, but I don't know what you mean by "translate" in this context.

 

[nonequilibrium]

Ah, maybe I'm using the wrong verb? (English is not my mother language)

I mean translational motion, defined by: take an object and mark two random points A and B on the object; then the object goes through a translational motion if and only if at any later moment if you were to connect the place A and B were at (in your coordinate system) with your "new" points A' and B' (on your object) those two lines are parallel. Another definition is: not rotation ;)

 

[D H]

Of course it undergoes translational motion. That is what an orbit is. It's just not straight-line translational motion.

 

[Jack21222]

I thought every elementary school student knew that the Earth goes around the sun. That's why I thought the question was more complicated than it was.

 

[nonequilibrium]

Oh, okay... When I asked my professor of classical mechanics he said "no", although he wasn't very clear on it. Any idea what he could have ment? And after that I thought about it again and there was indeed something weird: we had proven in class that translational motion implies that any specific point continues to have the same velocity vector, but this can't be in the case of the Earth (even in the idealest of cases), because if a certain point is at one time closer to the sun than at another time, due to conservation of energy (potential difference...), the kinetic energy must be different. Can we ignore this for some reason due to connective forces?

EDIT: Jack, I don't know if the question is that obvious? Well anyway when I asked it this week in my university course class, a lot students started snickering at the apparent stupidity of the question because they thought the Earth rotated around the sun.

 

[D H]

You are talking about uniform motion, which is quite different from translational motion.

Why would physicists and others use the term "translational dynamics" and write papers and books about "translational dynamics" if the concept of translation was restricted to the trivial case of uniform motion?

 

[Jack21222]

The correct astronomical terms are the Earth "rotating" around it's axis and "revolving" around the sun.

"Rotating" around the sun doesn't really mean anything.