Originally posted by andrew93
A quick search online (for the sake of curiosity given I'm not a mathematician) confirms I know absolutely nothing about circular momentum. I would have intuited the instantaneous (or average) acceleration at (or around) points A1 and A5 would be zero......but the 'web and the wording of your question suggests otherwise.....and that I don't understand acceleration as much as I thought I did.
On the contrary, at points A1 and A5, the pendulum's instantaneous velocity
should be 0, and the pendulum is starting a freefall at -9.8m/s^2 until the string exerts force on it.
At any given point, the acceleration of the pendulum should be the sum of the two vectors of gravitational acceleration (g) and g * cos(theta) in the direction of the pin, where theta is the angle between the string and vertical.
I believe this results in an instantaneous acceleration of g * sin(theta) along the tangent to the arc.