# What is the right word / an analogy for a "pendulum" that gains momentum with each swing?

I'm trying to find the right word / concept to describe the following effect:

Consider a pendulum, except with each swing it gains momentum. The exchange of potential and kinetic energy is not equal, instead increasing with each shift.

Another way to describe the concept: you're trimming a bush and you want it to be symmetrical. You take a little off the left, you take a little off the right, then you step back and --crap, it's uneven. So you take a little more off the right and --crap, uneven on the left now. You keep going until you don't have a bush anymore, just a weird amalgamation of branches.

Surely there is some physical or social scientific term that describes this concept. I've exhausted my Googling capabilities, can anyone offer guidance?

• the phrase 'progressively worse' or 'progressively more' comes to mind.
– DPT
Commented May 22, 2018 at 16:09
• incremental miscalculation? Doesn't quite ring true. If you are looking for a single/two word combination to express the idea, english.se could be a better fit (as dan suggested). See this meta post if you are having trouble deciding. You can flag and request the moderators to migrate the question for you. Good luck, I'm interested to find out what it is, as it's been driving me crazy all afternoon.
– EveryBitHelps
Commented May 22, 2018 at 17:50
• Cyclical asymmetry? Reiterative overcompensation? ;) (I doubt there's an actual word for this, but I could be wrong. If there is, it's likely scientific.) Commented May 23, 2018 at 4:49
• SMI: Shrubbery Maintenance Incompetence. Commented May 23, 2018 at 10:12
• How about over-correction? Commented May 23, 2018 at 16:54

In a control system we would call this Instability or divergence (as in, your shrubbery trimming algorithm cannot converge on a solution). For math, look at Divergent Series; i.e. your series of pendulum swings or bush trimming corrections fails to converge in time to a steady state solution (whereas, a model pendulum might repeat the same cycle forever, or IRL frictional damping (both in air and on the axle) would eventually bring it to standstill).

We can also see this as chaotic behavior. Look at that link and you will see an animation of a chaotic pendulum, along with other fun animations and pictures.

Regular pendulum motion and other such oscillations are described as

harmonic oscillation.

Wikipedia

Irregular oscillations are termed

non-harmonic or anaharmonic oscillations.

Physics Stack Exchange "What is the difference between Non-harmonic oscillation, Anharmonic oscillation and Complex harmonic oscillation?"

American Journal of Physics "Theory of a nonharmonic oscillator".

• This is a very helpful answer, and not too dissimilar from the answer I've chosen as the solution. Thank you very much! Commented May 24, 2018 at 14:00

accelerate (ed) Merrim-Webster

With accelerated errors, my efforts to trim the shrub resulted in a mere twig!

to cause to move faster

https://www.merriam-webster.com/dictionary/accelerate

'Reinforcing feedback loop' -- I believe this is a term from systems engineering, and it seems to describe what you're getting at. See http://www.systems-thinking.org/theWay/sre/re.htm