Animating a Pendulum with “Animate” and “True” Graphics:

ClearAll["Global`*"];

g=9.8;(* gravitational acceleration in m/(s^2)*)
len=1; (* length of pendulum arm, in meters*)
rb=0.05; (* radius for drawing of ball, as fraction of length *)
period=2*π*(Sqrt[(len/g)]); (* period in seconds *)
amplitude = 0.5 ;(* Initial amplitude, in radians *)
duration=4*period; (* Duration of animation *)
ϕ[t_]:=amplitude Cos[((2 π t)/period)];

plotbob[tmax_]:=Animate[Graphics[{{Thin,Blue,Line[{{0,len},{len*Sin[ϕ[t]],len*(1-Cos[ϕ[t]])}}]},{PointSize[rb/len],Red,Point[{len Sin[ϕ[t]],len (1-Cos[ϕ[t]])}]}},Frame->False, PlotRange ->{{-len,len},{-.25 len,1.25len}}],{t,0,tmax}]
(*
Summary of the Graphics Commands used here:
  The first one is "Line". The preceding adjectives (thin, blue) are obvious. The word line is followed by 4 numbers, in two pairs:
     {0,len} refers to the {x,y} coordinates at the TOP of the pendulum.
   The next pair are the {x,y} coordinates for the bob as a function of time. 
The second graphical command used here is "Point". The preceding adjectives (pointsize, Red) are also obvious. 
       {x, y} refers to the location of this point, and it is obvious that the point is at the same position as the bottom of the earlier line.
  In this group of two "graphics", drawings are added in the order listed. As a result, the red "point" is ON TOP of the blue line. 
  If you switched the order, you would see the blue line extend to the CENTER of the red ball, whereas in this version,
    the blue line extend under the red ball to its center.
Besides "Line" and "Point", some other options are: rectangle, polygon, circle, and disc.
Point, Circle, and Disc are all similar. Circle is hollow, but Disc is filled with some color. 
This sketch (made in Word) shows how I scaled the boundaries of the plot compared to the origin, etc.


*)
(* Note: this ANIMATE command generates all the animation frames, but doesn't show them *)
(* Note: In this animation, (0, 0) is at the bottom of the swing, not the top of the string *)
(* Note: You can't use "Manipulate" for this because it's not a plot, it's a drawing made with a "Graphics" command *)
(* Note: In this version, I'm not bothering to save the movie to an external file. But, see the next demo... *)

pendplot=plotbob[duration] (* this line SHOWS the animation *)