The Most Mind-Blowing Aspect of Circular Motion
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it when explaining that forces and tension changes propagate through a string or spring at a finite speed rather than instantly.
Recommended by 3 people across 3 different months, 2024 to 2024.
What it is
A physics explainer from the All Things Physics channel examining what really happens when a ball swung on a string is released, including experiments and a slinky simulation. It shows the surprising delay and wave propagation behind the loss of centripetal force, drawing on an American Journal of Physics paper.
What people said
Recommends jhole · 2024-08 · Physics Stack Exchange · on “Does spring stop applying force as soon as we cut it?”
have a look at [this video] which shows real world experiments of a very similar situation (I would summarize: every change can only propagate with finite speed in reality)
Recommends JEB · 2024-10 · Physics Stack Exchange · on “Why is the centrifugal force radially outwards?”
@Lukas Nullmeir's answer is correct, but not direct enough for my tastes: In an inertial frame there is no centrifugal force, period, full stop, end-of-story. The centrifugal is a so-call fictitious force that appears in rotating frames. In a frame rotating at $\vec \Omega$ (and $m=1$ ): $$ F_c = -\vec \Omega \times (\vec \Omega \times r) $$ That expands to: $$ \vec F_c = -\Big(\vec\Omega(\vec \Omega \cdot \vec r) - \Omega^2 \vec r \Big)$$ Now I can arbitrary define $\vec \Omega = \hat z$ to show $$ \vec F_c = \vec r - \hat z (\hat z \cdot \vec r) $$ where the right hand side is the vector rejection of $ \vec r$ onto $\vec z$ ( [LINK] ), that is, it's the complement of the vector projection,
Recommends march · 2024-12 · Physics Stack Exchange · on “Why is Centripetal force effect loss a delayed process?”
The speed of sound (i.e., long wavelength speed of waves) in a material determines how fast "information" gets from one place to another. When the string snaps, this creates a wave pulse that will travel down the length of the string. Only once this pulse hits the end of the string (where position of the stone) does the stone stop feeling the inward centripetal force. This pulse takes a non-zero amount of time due to the finite speed of waves in the string. It's easiest to understand this by replacing the string with a slinky and understanding how the "tension" in the slinky is cause by the different coils in the slinky pulling on each neighboring coil. If one coil goes slack, that causes th