Can someone please explain to me why the magnitude of gravity is lowest at the minimum potential energy and highest at the highest potential energy. I don't get this.
Thanks!
If I remember correctly, the magnitude of gravity, g, is the same at all points of the pendulum swing. What you may be referring to is the force due to gravity,
Fg. The reason Fg differs from point to point is due to the angle the string makes with the point of attachment. At the lowest point, the force due to gravity points straight down, also at this point, the tension force, which is created by the string, points straight up. This in effect creates a net force of zero. While at this lowest point, the string is at zero displacement from equilibrium, it thus has zero potential energy and maximum total kinetic energy.
The same can be said for when the pendulum bob is at its highest point (when it is at its full swing). The force due to gravity points straight down, which in effect gives the total force on the bob from gravity the total value of Fg and not some trig function of Fg. While at the point, the bob is at a maximum displacement from equilibrium and thus has a maximum potential energy, and zero kinetic energy.
Sorry if i made this more confusing than it should have been, pendulums I feel, require pictorial representation to be best understood.
