Belly flops into pools are a familiar summertime experience for many, marked by a loud smack and a painful sting. While the reason behind the pain has long been a topic of curiosity, it is now explained by Daniel Harris, an assistant professor in Brown University’s School of Engineering. According to Harris, the sudden transition from air to water causes the water surface to resist, leading to a “signature slam” that generates the sharp sting.
Fluid mechanics plays a crucial role in understanding this phenomenon, not only for recreational purposes but also for naval and marine engineering. Structures in these fields must withstand high-impact forces experienced during air-to-water transitions. Researchers at Brown University, in collaboration with scholars from the Naval Undersea Warfare Center and Brigham Young University, conducted a study to gain novel insights into this area.
Their study, published in the Journal of Fluid Mechanics, involved an experiment using a blunt cylinder that imitated a belly flop. However, they introduced a new twist by attaching a soft “nose” to the cylinder using flexible springs, simulating the impact load distribution and dampening strategy.
Surprisingly, the results showed that the flexible system did not always soften the impact, contradicting conventional wisdom. In fact, sometimes the flexible system increased the maximum impact force on the body compared to a fully rigid structure. Further experiments and theoretical modeling revealed that the vibrations from the structure upon entering the water compounded the slamming force. The researchers identified the key to be the spring’s softness, which must be adjusted appropriately to absorb the impact without causing excessive vibrations.
This study opens up new avenues of research, drawing inspiration from diving birds that perform specific maneuvers to reduce high forces during water entry. The researchers aim to develop a robotic impactor that can actively adjust during water entry to mitigate the impact on blunt objects.
Understanding the physics of impacting water not only gives valuable insights into summer pool activities but also has practical applications in improving engineering designs for structures that face air-to-water transitions. By studying the interaction between flexible systems and water, researchers are paving the way for more effective impact mitigation strategies.
Q: Why do belly flops hurt?
A: Belly flops hurt because the forces from the water surface resist the sudden transition from air to water, leading to a slamming impact that causes pain.
Q: How can understanding belly flops help naval and marine engineering?
A: Understanding the physics of belly flops is important for naval and marine engineering because it provides insights into high-impact forces experienced during air-to-water transitions, helping improve the design of structures that need to withstand such forces.
Q: What did the researchers discover in their study?
A: The researchers discovered that using a flexible system with springs to soften the impact of a belly flop did not always work as expected. In some cases, the flexible system actually increased the maximum impact force on the body. They found that the vibrations from the structure upon entering the water compounded the slamming force, and the key to mitigating this was adjusting the softness of the springs.
Q: What are the next steps in the research?
A: Inspired by diving birds that perform maneuvers to reduce high forces during water entry, the researchers aim to design a robotic impactor that can actively adjust during water entry to mitigate the impact on blunt objects.