Yeah, these researchers should have included a cafe server or two in their study - the people that walk with coffee for a living, kinda makes sense.
Having been a cafe server for 4 years I can say from experience that you can practically run with a cup of coffee without spilling it. Several times a day I would pour a cup of coffee while I brought it to a table - often without constantly looking at it, my eyes were always scanning tables.
That said - if you take enough steps with a full cup of coffee it will eventually spill, that's something that us wait staff actually talked about. We rarely spilled coffee.
You can walk with rhythm and still not spill if you hold your arm loose to decouple it from your body's motions. Let the cup have it's own inertia and have your arm follow your cup.
A lot of this has to do with the fact that you cannot feel velocity, you can only feel acceleration. So if you're walking and the coffee isn't spilling, you can increase your velocity at a constant rate (because you intuitively think it's the speed that matters). But when you stop, if you don't first slow down at a constant rate, then you're acceleration will change abruptly and you spill your coffee (because you intuitively think stopping won't matter).
Who is funding this garbage? There are tons of ways to walk without spilling. this is a childrens task that only requires practice to internalize a personal algorithm of motion. Always asking can Science but never asking how Science
Having been a cafe server for 4 years I can say from experience that you can practically run with a cup of coffee without spilling it. Several times a day I would pour a cup of coffee while I brought it to a table - often without constantly looking at it, my eyes were always scanning tables.
That said - if you take enough steps with a full cup of coffee it will eventually spill, that's something that us wait staff actually talked about. We rarely spilled coffee.