Rotation vs Revolution

[Gareth56]

It's said that Rotation is when an [rigid] object turns about an internal axis e.g. a merry-go-round or gramophone record whereas Revolution is when an object turns about an external axis e.g. the Earth around the Sun.

 

So why are gramophone record speeds given in terms of Revolutions Per Minute (RPM) and not Rotations Per Minute because the whole of the record is rotating about an internal axis?

[Sisyphus]

Maybe it's just a misnomer. Or maybe it's because the needle is doing a revolution around the record? It seems like it's just a matter of perspective: the Moon revolves around the Earth, or the Earth-Moon system is rotating?

[swansont]

It's said that Rotation is when an [rigid] object turns about an internal axis e.g. a merry-go-round or gramophone record whereas Revolution is when an object turns about an external axis e.g. the Earth around the Sun.

 

So why are gramophone record speeds given in terms of Revolutions Per Minute (RPM) and not Rotations Per Minute because the whole of the record is rotating about an internal axis?

 

Perhaps because it wasn't physicists who tagged them as being revolutions per minute. We'd have denoted them in terms of angular frequency, anyway, i.e. radians per second.

 

On a related not, revolver pistols suffer from the same mis-labeling. But the people who made the mistake are armed, so who's going to argue with them?

[Sisyphus]

Also revolving doors and revolving restaurants.

[D H]

It's said that Rotation is when an [rigid] object turns about an internal axis e.g. a merry-go-round or gramophone record whereas Revolution is when an object turns about an external axis e.g. the Earth around the Sun.

That distinction is particular to astronomers.

 

So why are gramophone record speeds given in terms of Revolutions Per Minute (RPM) and not Rotations Per Minute because the whole of the record is rotating about an internal axis?

Because they are astronomers.