Well, you'll have to use a little bit of physics, but you don't need to *simulate* any physics. There are formulas for [pendulum][1] motion you can easily use to set the rotation of your pendulum. For small swings, the motion can be approximated with [simple harmonic motion][2]. 

The angular displacement at a specific time can be approximated with:


![enter image description here][3]

This is most accurate for a small maximum θ, but will likely be accurate enough for your purposes. Create a function that takes the current time, and outputs the angle for which your pendulum should be rotated, and rotate your sprite by that amount.


  [1]: https://en.wikipedia.org/wiki/Pendulum
  [2]: https://en.wikipedia.org/wiki/Simple_harmonic_motion
  [3]: https://i.sstatic.net/YdFrT.gif