Inflection means a point where the concavity of the function switches directions, and the function locally has zero curvature. It could coincide with a stationary point, like it does in y=x^3, or it could be some place entirely different, like it is for a "roller coaster" cubic, such as y = x*(x - 6)^2, at the point of x=4, y=16. In beam theory, it's called a point of contraflexure, where the deflection curve switches from "frowning" to "smiling".
So you never use the abbreviation "POI" except you do it in the very same video you tell us you never do it.
what does point of inflection mean in the real world- is it when acceleration changes (does it change direction or velocity)?
Inflection means a point where the concavity of the function switches directions, and the function locally has zero curvature. It could coincide with a stationary point, like it does in y=x^3, or it could be some place entirely different, like it is for a "roller coaster" cubic, such as y = x*(x - 6)^2, at the point of x=4, y=16.
In beam theory, it's called a point of contraflexure, where the deflection curve switches from "frowning" to "smiling".
This is 3/4
I THINK theres a reason they reordered it this way
It's both 3 and 5.