To put the questions differently: assume we look at all the planets from the perspective of a single point (say, Earth), why do some spin one way (cw) and some spin the other way (ccw)? Are cc and ccw evenly distributed?
They seem to spin in different directions because you are observing them from a single point - earth.
Consider the following. You and I are standing on opposite sides of a pane of glass. I spin a wheel parallel to the pane of glass and we both observe it. From my side of the glass the wheel is spinning clockwise. From your point of view (because you are seeing the opposite side of the wheel) it is spinning counterclockwise.
Whether a given rotation is clockwise or counterclockwise depends entirely on your reference frame - they really don't have a robust definition that doesn't depend on the pov of the observer.
There is a really excellent and clear description of the problem and solution to this that is employed in classical mechanics here[1] but if you only care about the solution, by convention we employ the right hand rule. If you and I both agree a common direction in the plane of rotation of the wheel say parallel to the floor off to the side (whichever side doesn't matter but for one of us it will be to the left and the other right), point our right hand index finger in that direction (called r hat or the direction of radial motion) and curl our two smallest fingers in the direction of rotation of the wheel, our thumbs will be pointing parallel with one another. This would be called n hat (normal motion), and is the direction of any vectors which are the cross product of two vectors in the plane of rotation of the wheel. As a bonus if you make your right hand middle finger perpendicular to the index finger you have theta hat (tangential motion). Now even though you and I can't agree whether the wheel is spinning clockwise or counterclockwise we have three identical basis vectors and can use these to form a common polar coordinate system to describe this rotating system.
I'm trying to say it doesn't matter where you observe it from. If one thing is spinning one way, and another the opposite way. Whether you see it from your side, or my side, the directions of the two things are opposite. Am I wrong?
seanhunter|1 year ago
Consider the following. You and I are standing on opposite sides of a pane of glass. I spin a wheel parallel to the pane of glass and we both observe it. From my side of the glass the wheel is spinning clockwise. From your point of view (because you are seeing the opposite side of the wheel) it is spinning counterclockwise.
Whether a given rotation is clockwise or counterclockwise depends entirely on your reference frame - they really don't have a robust definition that doesn't depend on the pov of the observer.
There is a really excellent and clear description of the problem and solution to this that is employed in classical mechanics here[1] but if you only care about the solution, by convention we employ the right hand rule. If you and I both agree a common direction in the plane of rotation of the wheel say parallel to the floor off to the side (whichever side doesn't matter but for one of us it will be to the left and the other right), point our right hand index finger in that direction (called r hat or the direction of radial motion) and curl our two smallest fingers in the direction of rotation of the wheel, our thumbs will be pointing parallel with one another. This would be called n hat (normal motion), and is the direction of any vectors which are the cross product of two vectors in the plane of rotation of the wheel. As a bonus if you make your right hand middle finger perpendicular to the index finger you have theta hat (tangential motion). Now even though you and I can't agree whether the wheel is spinning clockwise or counterclockwise we have three identical basis vectors and can use these to form a common polar coordinate system to describe this rotating system.
[1] https://www.youtube.com/watch?v=q785KV5ZIN0&t=45s
pushupentry1219|1 year ago