A recent article explores how the flexibility of containers impacts the speed at which they drain.
As Rohit Velankar, a senior at Fox Chapel Area High School, filled a glass with juice, he noticed the rhythmic glug, glug, glug sound caused the carton walls to flex.
Rohit reflected on the sound and questioned whether a container’s flexibility affected how its contents drained. He started looking for answers for his science fair project, but it developed into a larger study when he partnered with his father, Sachin Velankar, a chemical and petroleum engineering professor at the University of Pittsburgh Swanson School of Engineering.
The two set up an experiment in their basement, and their discoveries were documented in their first research paper together.
“As a scientist, I became pretty invested in the project,” said Sachin Velankar. “We decided that once we began the experiments, we would see them through to the end.”
The Science Behind the Glug
Rohit’s initial tests revealed that deli containers with rubber lids drained faster than those with plastic lids.
“Glugging happens because the water flowing out reduces the pressure inside the container,” said Velankar. “In highly flexible containers, like those used for IV fluids or boxed wine, fluids can be released without glugging. However, there are various kinds of flexible bottles out there, so their elasticity must influence the draining speed.”
They constructed their own specialized acrylic bottles with rubber lids using tools from the makerspace at Fox Chapel Area High School. Each bottle had a sensor positioned near a hole at the bottom to monitor pressure changes with each glug. The Velankars simulated flexibility by changing the hole’s diameter, confirming that flexible bottles drain more quickly but produce larger, less frequent glugs.
