OVERLAP - I thought i knew...

When it comes to the principles of animation I feel like most people can grasp the concepts behind them pretty easily. After all that's the way objects move in real life. Overlap for example; objects at rest tend to stay at rest and objects in motion tend to want to stay moving. When an elephant stops walking, his trunk will swing forward and then back again. Simple! Or so i thought...

The other day at work I was trying to animate some tentacles moving around and overlapping. As I was struggling away my friend and colleague sat next to me (Kayn) saw what I was doing and decided to give me an old school Disney lesson in overlap. Which went as follows:


He handed me a sketch which looked like this one below:

He then asked me what would happen to the string if the top were to start moving to the right, as if someone pulled it. I drew this...

WRONG!!! 

Though this felt like the only solution it was in fact incorrect. In my mind I thought "well the end of the string will want to stay at rest but I suppose it will have to move a bit". Well yes that is true but it won't look like the above. It will in fact look like the diagram below: 

The end of the string moves to the left!! My mind blew up a little bit at this point. As the string is pulled it's height shortens causing the end to move up and left. Try this at home now by holding a pencil at one end and moving it right rapidly. The end will drag left first. 

 It also gives us this really wonderful S curve and curve reversal in the end of the string. This S curve appears again if the string were to stop moving too. 

As Kayn corrected my drawing like the one above I could finally understand why my overlapping tentacles weren't looking too hot. Even though i felt like I grasped the concept of overlap, I didn't really understand it. And that's where the difference is. So, time to revisit all the principles and really understand the secret mechanics of them all.