Similarly, the difference in how smooth spillable containers were transferred (compared to unspillable ones) decreased as the containers got narrower, but only when the water level was near the rim.

When there was a large gap between the water level and rim, the effect of diameter was diminished.

Meanwhile, movement time and smoothness were influenced by both h and d. Here, d's effect was only apparent for low h values.

In other words, movement time differences only varied with the container's narrowness when the water level was close to (and not far from) the container's rim.

Furthermore, TwS got easier as h increased (water surface further from container rim) and as d decreased (container is narrower).

Specifically, the difference in peak velocity and first peak acceleration between spillable vs. unspillable containers increased with h but was unaffected by d.

The different h and d values yielded different θ values. Results showed that as θ increased, participants:

- Moved faster
- Moved the container with a larger initial acceleration
- Showed smoother movements

This shows that as θ increases, participants feel that the liquid is less likely to spill.

To investigate the informational variables involved in the affordance for TwS, Xu, Wang & Pan (2023) recorded participants' movement differences when transferring spillable vs. unspillable containers.

Then, they analysed how these movement differences varied with different h and d values.

To successfully control this action, one must perceive the possibility of transferring the container without spilling, i.e., the container's affordance for transfer without spilling (TwS).

Here, this affordance might be defined by the critical angle (θ) that determines when spilling would occur.