FEB 06, 2016 7:42 AM PST

The Science of Skipping Spheres

WRITTEN BY: Cassidy Reich
In a recent paper whimsically titled “Elastic spheres can walk on water,” a group from Utah State University have empirically shown why it is easier to skip an elastic sphere (such as the water toy the WaBoBa) on water compared to a rigid sphere.

This kind of research does actually have a lot of practical implications beyond being a fun thing to do at the lake. Inflatable boats exhibit different behavior on water compared to a boat made of more rigid material, and it is important to understand why. Specifically, the Navy thinks it is important to understand why considering they were the ones who funded this research.

The physics of how a stone skips on water have been well-studied. Briefly, that phenomenon can be described as “an object obliquely impacting a water surface with sufficient inertia will carve a cavity on the air-water interface and experience a pressure-driven hydrodynamic force dependent on object velocity, geometry, and orientation.” That is a very science-y way of saying what you’ve probably figured out through trial-and-error: the stone needs to be kind of flat and thrown in the right way (more out, less down) and at the right speed to skip.

To gt a rigid sphere to skip (which is much harder than the favored flat stone), the impact angle on the water has to be below an upper limit, termed βo. An elastic sphere’s βo is up to three times larger than a rigid sphere’s so there is a much larger window of acceptable impact angles to get an elastic sphere to skip. This expanded βo (plus a lot of other intense mathematics) means that elastic spheres can do multiple skips over long periods of time.



In addition to tolerating higher impact angles, elastic spheres actually deform upon impact with water, giving them the more favorable disk shape that we all know works better for skipping rigid stones. In this slow-motion clip of an elastic sphere hitting the water, you can see how it flattens out on impact.



Hilariously, this line of research got started simply because the senior researchers’s son and nephew wanted to see a slow motion video of a rubber ball skipping on water. That curiosity led to important and translational discoveries on the way elastic objects interact with the surface of water.

Sources: EurekAlert and Nature Communications
About the Author
  • Cassidy is a curious person, and her curiosity has led her to pursue a PhD in Pharmacology at the New York University Sackler Institute of Biomedical Sciences. She likes to talk about science way too much, so now she's going to try writing about it.
You May Also Like
SEP 10, 2020
Chemistry & Physics
Reprogramming Virus to Build Better Li-ion Batteries
SEP 10, 2020
Reprogramming Virus to Build Better Li-ion Batteries
There's no doubt that the word "virus" is currently on everyone's mind. However, there's a lot mor ...
SEP 14, 2020
Chemistry & Physics
Using a laser to cool a polyatomic molecule has never been done before - until now
SEP 14, 2020
Using a laser to cool a polyatomic molecule has never been done before - until now
Scientists from Harvard have devised a technique that allows them to slow down a polyatomic molecule using a laser. This ...
OCT 02, 2020
Chemistry & Physics
A New Way of Building Houses: 3-D Printing with Clay
OCT 02, 2020
A New Way of Building Houses: 3-D Printing with Clay
Our ancestors had a long history of building dwelling structures using clay and plant-based fibrous materials. Even thes ...
NOV 02, 2020
Chemistry & Physics
Eliminating CO2 at room temperature
NOV 02, 2020
Eliminating CO2 at room temperature
A new chemical process developed by researchers at the National Institute of Standards and Technology (NIST) demonstrate ...
NOV 09, 2020
Cell & Molecular Biology
The Science Behind Wine Fraud Prevention
NOV 09, 2020
The Science Behind Wine Fraud Prevention
Wine comes in a wide range of flavors and prices. Wine fraud, in which cheaply produced wine is passed off as the expens ...
NOV 17, 2020
Clinical & Molecular DX
Tumor Stiffness Linked to Its Aggressiveness
NOV 17, 2020
Tumor Stiffness Linked to Its Aggressiveness
  As tumors grow, tiny areas at their cores are found to become stiff prior to metastasis, or the spread of cancer ...
Loading Comments...