Symbol r_a
is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.
Read this term in its guide →Published equation contexts
Why this formula appears here
Start with the least controversial position anyone has ever assigned to an extended body: the Newtonian, mass-weighted centroid, = / , a sum over the body’s constituent mass elements at positions , evaluated at one common instant. That last clause is doing all the work relativity is about to object to. “One common instant” means one value of a time coordinate t shared by every term in the sum — the coordinate time of whichever inertial frame is doing the summing, not any single mass element’s own proper time along its own worldline — and which value of t counts as simultaneous with which is exactly the freedom special relativity…
Read the representative guide
How to interpret it
Read this expression with the definitions, units, and assumptions supplied by the article.
Research cited beside this formula
Published contexts (1)
A symbol can carry a different meaning in another article. Each occurrence keeps its own guide and term definitions.
Equation 3 · Evolutionary Physics
The Atlas That Refuses to Close
This mathematical expression combines the displayed quantities; its precise role follows from the surrounding article text.
Start with the least controversial position anyone has ever assigned to an extended body: the Newtonian, mass-weighted centroid, = / , a sum over the body’s constituent mass elements at positions , evaluated at one common instant. That last clause is doing all the work relativity is about to object to. “One common instant” means one value of a time coordinate t shared by every term in the sum — the coordinate time of whichever inertial frame is doing the summing, not any single mass element’s own proper time along its own worldline — and which value of t counts as simultaneous with which is exactly the freedom special relativity…
Equation guide → · Article →