- #1
mgkii
- 138
- 42
I used to think I understood this - big mistake!
I've just watched a great classic Feynman lecture posted by another PF user (a superb way to spend 50 mins of you can spare the time)
https://www.physicsforums.com/threads/i-found-the-best-teacher-of-physics.855335/
In that lecture, Feynman describes the tidal effect of the moon on the Earth (26 mins in), and gives two components to it; the (obvious?) inverse cube tidal effect on the different sides of the earth, and the (lesser discussed?) centrifugal effect arising from the Earth and moon rotating around a common point of focus which is inside the earth, but always on moon-side of the Earth and therefore the water on the side furthest from the moon is "thrown off" more than the other side (Fenyman's words).
I wanted to understand more about these two components and if they balance out exactly to produce an identical effect on both sides of the Earth and ran into confusion. Articles fall into 4 camps - I've linked to examples, but they're not the only ones I looked at.
i. The centrifugal force** should be ignored as it's mixing up a rotating frame of reference from POV of the Earth and a static frame from a tidal force POV
https://www.lhup.edu/~dsimanek/scenario/tides.htm
(The article correctly differentiates between centripetal force and centrifugal force. I'll continue to use Centrifugal force in the way the articles do from here on)
ii. It's all down to Centrifugal force
http://www.moonconnection.com/tides.phtml
iii. It's both
http://www.livescience.com/29621-what-causes-the-tides.html
https://tidesandcurrents.noaa.gov/restles3.html
iv. And probably the least helpful... It's like this - No you're wrong, I'm right - NO! I'm right - No It's ME!
https://en.wikipedia.org/wiki/Talk:Tidal_force
This last one even says categorically that Feynman was wrong in his description. And then later someone else says he wasn't. So that wasn't exactly conclusive!
So what's my question? Well if I'm allowed two of them:
1. Are the "two components" actually just two ways of looking at the same force in rotating and a static reference frame, or are there really two separate components that make up the the overall force in play?
2. Does whatever the answer is to 1, result in (theoretical) identical sized bulges on both sides of the earth?
And I suppose there's a third... does anyone have a reference source they firmly believe to be "the right answer"?
Thanks
Matt
I've just watched a great classic Feynman lecture posted by another PF user (a superb way to spend 50 mins of you can spare the time)
https://www.physicsforums.com/threads/i-found-the-best-teacher-of-physics.855335/
In that lecture, Feynman describes the tidal effect of the moon on the Earth (26 mins in), and gives two components to it; the (obvious?) inverse cube tidal effect on the different sides of the earth, and the (lesser discussed?) centrifugal effect arising from the Earth and moon rotating around a common point of focus which is inside the earth, but always on moon-side of the Earth and therefore the water on the side furthest from the moon is "thrown off" more than the other side (Fenyman's words).
I wanted to understand more about these two components and if they balance out exactly to produce an identical effect on both sides of the Earth and ran into confusion. Articles fall into 4 camps - I've linked to examples, but they're not the only ones I looked at.
i. The centrifugal force** should be ignored as it's mixing up a rotating frame of reference from POV of the Earth and a static frame from a tidal force POV
https://www.lhup.edu/~dsimanek/scenario/tides.htm
(The article correctly differentiates between centripetal force and centrifugal force. I'll continue to use Centrifugal force in the way the articles do from here on)
ii. It's all down to Centrifugal force
http://www.moonconnection.com/tides.phtml
iii. It's both
http://www.livescience.com/29621-what-causes-the-tides.html
https://tidesandcurrents.noaa.gov/restles3.html
iv. And probably the least helpful... It's like this - No you're wrong, I'm right - NO! I'm right - No It's ME!
https://en.wikipedia.org/wiki/Talk:Tidal_force
This last one even says categorically that Feynman was wrong in his description. And then later someone else says he wasn't. So that wasn't exactly conclusive!
So what's my question? Well if I'm allowed two of them:
1. Are the "two components" actually just two ways of looking at the same force in rotating and a static reference frame, or are there really two separate components that make up the the overall force in play?
2. Does whatever the answer is to 1, result in (theoretical) identical sized bulges on both sides of the earth?
And I suppose there's a third... does anyone have a reference source they firmly believe to be "the right answer"?
Thanks
Matt