Orbital and spin angular momentum

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Discussion Overview

The discussion centers on the formulas for orbital and spin angular momentum, exploring both classical and quantum mechanical perspectives. Participants examine the differences between these types of angular momentum and how they are calculated in various contexts, including classical rigid body rotation and quantum mechanics.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires whether the formula J=mvr applies to orbital or spin angular momentum, suggesting confusion about their definitions.
  • Another participant asserts that J=mvr is specifically for orbital angular momentum in a classical sense and states that spin cannot be expressed with such classical formulas.
  • A follow-up question asks how to calculate spin angular momentum, particularly for Earth and black holes, indicating a need for clarification on the application of angular momentum concepts.
  • Another participant emphasizes the distinction between particle spin (as in quantum physics) and the spin of macroscopic objects like Earth, suggesting that the latter can be calculated using the formula L = Iw for rigid body rotation.
  • There is a reiteration that angular momentum and spin for quantum objects are not defined by classical formulas, highlighting the complexity of the topic.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of classical formulas to spin angular momentum, indicating that there is no consensus on how to reconcile classical and quantum perspectives on angular momentum.

Contextual Notes

Participants note that the definitions and calculations of angular momentum depend on the context, such as classical versus quantum mechanics, and the nature of the object being considered (e.g., particles versus rigid bodies).

spidey
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what are the formulas for orbital and spin angular momentum? Or both have the same formula?

The formula J=mvr is for orbital or spin angular momentum?
 
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spin is not a derivable quantity in the sense if orbital angular momentum. So you can't have such a classical expression for it.

J=mvr is the orbital angular momentum, albeit in a the classical sense.

quantum mechanically one can't have such formulae. Its a bit different in this regime.
 
vkroom said:
spin is not a derivable quantity in the sense if orbital angular momentum. So you can't have such a classical expression for it.

J=mvr is the orbital angular momentum, albeit in a the classical sense.

quantum mechanically one can't have such formulae. Its a bit different in this regime.

if J=mvr is the orbital angular momentum then how to calculate spin angular momentum..

for example,earth spins on its own axis so how to calculate Earth's spin angular momentum...some black holes also spin so how to calculate?
 
dude, u shud be clear as to what you mean by spin.

if its the usual spin in physics, i.e. the one ppl talk abt in particles like electrons, then its not what u are writing here.
if its Earth's spinning rate u want to know, then its still the same old angular momentum, bt for something known as a "rigid body" rotation. its given as : L = Iw. wiki a bit and u'll be through.

angular momentum and spin for quantum object are not defined by such formula as mentioned above.
 

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