Tag: Tokyo2020

Tokyo 2020: Optimizing Oar Length

The sleek hulls of racing boats are designed to minimize drag, but there’s optimization to the oars as well. Mathematical models – and the history of rowing – indicate that shorter oars are more ideal for the sprint-style races seen in the Olympics. Shorter oars may be less efficient at transferring energy, but they’re easier to move quickly, and an athlete’s higher stroke rate more than makes up for the loss of efficiency. (Note that the advantage only holds for sprint events; in endurance events, a longer oar is preferable because holding a high stroke rate for a long time is difficult.)
Physicists have taken this a step further by building a mathematical model that predicts the optimal oar length for a given athlete, based on their height, strength, and other characteristics. They validated their modeling with a robotic rowboat. They note, however, that the effects are really only useful for elite rowers. Amateurs are better served by learning proper technique than they are by using an optimal length oar. (Image credit: J. Calabrese; research credit: R. Labbé et al.; via APS Physics)
We’re celebrating the Olympics with sports-themed fluid dynamics. Learn how surface roughness affects a volleyball serve, see the wingtip vortices of sail boats, and find out about the physics of surfing. And don’t forget to come back next week for more!
July 30, 2021
Tokyo 2020: Sailing Physics
At first glance, sailboats don’t look much like an airplane, but physics-wise, they’re closely related. Both the sail and hull of a sailboat act like wings turned on their side. Just as with airplane wings, the driving force for a sail comes from a difference in pressure across the two sides of the sail. The same effects applied to the hull and its keel (the wing-like extension that sits below the hull) provide the force that keeps a sailboat from slipping sideways as it cuts a path through wind and water.
Like airplane wings, sailboats also generate tip vortices: one from the top of the sail, the other from the bottom of the keel. Those vortices are typically invisible, but in foggy weather, like in the photo below, you can see the tracks they leave behind. (Image credits: top – Ludomił; bottom – D. Forster; research credit: B. Anderson; submitted by Lluís J.)
Follow along all this week and next as we celebrate the Olympics with sports-themed fluid dynamics.
July 27, 2021
Tokyo 2020: Volleyball Aerodynamics
Like footballs and baseballs, the trajectory of a volleyball is strongly influenced by aerodynamics. When spinning, the ball experiences a difference in pressure on either side, which causes it to swerve, per the Magnus effect. But volleyball also has the float serve, which like the knuckleball in baseball, uses no spin.
In this case, how the ball behaves depends strongly on the way the ball is made. Some volleyballs use smooth panels, while others have surfaces modified with dimples or honeycomb patterns, and researchers found that these subtle changes make a big difference in aerodynamics. A float serve’s trajectory is unpredictable because the ball will swerve whenever air near the surface of the ball on one side goes turbulent or separates. And without spin to influence that transition, everything comes down to the ball’s speed and its surface.
Researchers found that volleyballs with patterned surfaces transition to turbulence at lower speeds, which makes their behavior more predictable overall. But players who want to maximize the unpredictability of their float serve might prefer smooth-paneled balls, which don’t make the transition until higher speeds. (Image credit: game – Pixabay, volleyballs – U. Tsukuba; research credit: S. Hong et al., T. Asai et al.; via Ars Technica)
Stick around all this week and next for more Olympic-themed fluid physics!
July 26, 2021