Tag: drag reduction

Disappearing Sea Ice Ridges
As blocks of sea ice shift and float, they can press together, forming ridges spaced every few hundred meters or so. A new study uses aerial observations from recent decades to show that these sea ridges are getting smaller in both size and number, a smoothing of Arctic topography that has many consequences.
The team showed that the overall changes in the sea ridges correspond to a loss of older sea ice. The current smoother sea ice presents less drag to winds and currents, which might suggest that the ice is slower-moving, but instead the opposite seems true. Scientists are not sure why the ice is moving faster, though faster ocean currents may play a role.
Another consequence of smoother sea ice is wider, shallower melt ponds each summer. These wider ponds increase the amount of sunlight the ice absorbs, hastening melting even further. (Image credit: USGS; research credit: T. Krumpen et al.; via Eos)
March 4, 2025
Paris 2024: Tennis Racket Physics
Like many sports that feature balls, spin plays a big role in tennis. By imparting a topspin or backspin to a tennis ball, players can alter the ball’s trajectory after a bounce and, using the Magnus effect to alter lift around the ball, change how it travels through the air. For example, a ball hit with backspin can dive just after the net, forcing an opponent to scramble after it. How much spin a player can impart depends on the speed of the racket’s head. Competitive rackets are carefully engineered — in terms of weight, string tension, and frame stiffness — to translate the kinetic energy of a player’s swing into the ball. But aerodynamics also play a role: new rackets designed to minimize drag hit the market 15-20 years ago, promising drag reductions up to 24% compared to previous rackets. That gives a player more swing speed and higher spins at a lower energy cost. (Image credit: C. Costello)
Related topics: The Magnus effect in table tennis and in golf; the reverse Magnus effect
Check out more of our ongoing and past Olympic coverage here.
August 6, 2024
Paris 2024: Cycling in Crosswinds
Wind plays a major role in cycling, since aerodynamic drag is the greatest force hampering a cyclist. In road racing, both individual cyclists and teams use tactics that vary based on the wind speed and direction. Crosswinds — when the apparent wind comes from the side in the cyclist’s point of view — are some of the toughest conditions to deal with. In races, groups will often form echelons to minimize the group’s overall effort in a crosswind. Alternatively, racers looking to tire their competitors out will position themselves on the road so that the rider behind them gets little to no shelter from the wind; this is known as guttering an opponent.
In this study, researchers put a lone cyclist in a wind tunnel and measured the effects of crosswind from a pure headwind to a pure tailwind and every possible angle in between. From that variation, they were able to mathematically model the aerodynamic effects of crosswind on a cyclist from every angle. With rolling resistance (a cyclist’s second largest opposing force) included, they found relatively few conditions where a crosswind actually helped a cyclist. Most of the time — as any cyclist can tell you — hiding from the wind is beneficial. (Image credit: J. Dylag; research credit: C. Clanet et al.)
Related topics: The physics of the Tour de France, how the peloton protects riders aerodynamically, track cycling physics, and a look inside wind tunnel testing bikes and cyclists
Catch all of our ongoing Olympics coverage here.
August 2, 2024
Paris 2024: Coordinating the Front-Crawl
Of all the swimming strokes humans have invented, none is faster or more efficient than the front-crawl. That’s why all competitors use it in freestyle events, and why it’s the only stroke that appears in races longer than 200 meters. But elite swimmers don’t perform the front-crawl the same way in a sprint as they do in a longer race. Instead, researchers found that swimmers use three different regimes of arm coordination.
For long-distance races, elite swimmers adopt a stroke that has only one arm in the water at a time. Each stroke is followed by a glide phase with one arm stretched in front of them. Researchers compared this to the burst-and-coast method that fish use to minimize the energy they use. As a swimmer’s speed increases, they shorten the glide phase and begin to maximize the force produced with each propulsive stroke.
In the third regime — the fastest one used by elite sprinters — the strokes of a swimmer’s arms are superposed, with both arms engaged in propulsion at the same time during parts of the cycle. This mode maximizes propulsive force but requires a lot of energy, so swimmers can only sustain it for a short while.
Since researchers built their observations into a physical model that explains how and why elite swimmers do this, the model can actually be used to advise individual swimmers on how they can adapt their stroke based on their size, desired speed, and other physical characteristics. (Image credit: J. Chng; research credit: R. Carmigniani et al.)
Related topics: More on swimming physics including why swimmers are faster underwater and how to design faster pools.
Find all of our current and past Olympics coverage here.
August 1, 2024
Paris 2024: Triathlon Swimming
Unlike the swimming competition, Olympic triathletes complete their swim legs in open waters. There are no lane dividers and no rules against drafting off a fellow athlete. Curious to see how draft positioning could affect swimmers, researchers experimented with swimmer-shaped models in a water channel and a numerical simulation. They found that the most advantageous position is directly behind a lead swimmer, where the follower could enjoy a 40% reduction in drag. Another good position is near the leader’s hip, where waves off the leader provide a 30% reduction in drag.
The worst place to swim, interestingly, is immediately side-by-side. With both swimmers neck-in-neck, drag is maximized, and each swimmer feels more drag than they would swimming by themselves! (Image credit: J. Romero; research credit: B. Bolan et al.)
Related topics: Drafting in each triathlon stage and drafting effects in nordic skiing
Join us all this week and next for more Olympics-themed stories.
July 30, 2024
Paris 2024: Swimsuit Tech
The aughts were an exciting time to watch competitive swimming. Records were falling left and right, especially in 2008 and 2009. The first wave of improvements came around 2000, with the introduction of full-body swimwear. According to one analysis, men’s freestyle swimming performances improved by about 1% with that change. The next big leap came in 2008 when companies introduced polyurethane panels into the suits (most famously the LZR Razer suits pictured above) causing an additional 1.5-3.5% performance improvement. The panels were stiff, reducing the swimmer’s cross-sectional area and thereby reducing drag. Their effect was greatest in sprint events; long-distance swimmers saw fewer improvements, possibly because turning in the stiffer suits was tiring.
The biggest leap came in 2009 with all polyurethane full-body swimsuits, which streamlined swimmers and gave them skin friction improvements that let them slip through the water more easily. Freestyle swimmers with those suits were showing a full 5.5% performance improvement on top of the 2000-era full-body suits.
With so many records falling in 2008 and 2009 — largely to swimmers wearing the expensive new suits that some teams could not afford — swimming’s federation chose to ban the new technology, causing an immediate drop in performances to pre-polyurethane levels. Although sprint performances will likely improve little by little each year, no one is likely to break the sprint records of 2008-2009 in the next decade — not unless the federation establishes a “new rules” record the way officials did with the javelin after a major rule change. (Image credit: Getty Images; research credit: L. Foster et al.)
Today kicks off our fluids-themed Olympics coverage. Stay tuned for more sports this week and next week. If that’s not enough sports physics for you, check out what we wrote in previous years.
July 29, 2024
Butterfly Scales
Catch a butterfly, and you’ll notice a dust-like residue left behind on your fingers. These are tiny scales from the butterfly’s wing. Under a microscope, those scales overlap like shingles all over the wing. Their downstream edges tilt upward, leaving narrow gaps between one scale and the next. Experiments show that, although butterflies can fly without their scales, these tiny features make a big difference in their efficiency.
At the microscale, a butterfly’s scales overlap like roof shingles but are tilted upward, leaving cavities in the downstream direction.
When air flows over the scales, tiny vortices form in the gaps between. These laminar vortices act like roller bearings, helping the flow overhead move along with less friction and, thus, less drag. Compared to a smooth surface, the scales reduce skin friction on the wing by 26-45%. (Image credit: butterfly – E. Minuskin, scales – N. Slegers et al., experiment – S. Gautam; research credit: N. Slegers et al. and S. Gautam; via Physics Today)
This lab-scale experiment shows how air moves over butterfly scales. As flow moves from left to right, small persistent vortices form in the gaps between scales. These act like roller bearings that reduce the skin friction from air moving past.
September 21, 2023
Drag Reduction for Swimming Shrimp
Marsh grass shrimp, despite their small size, are zippy swimmers. They move using a series of closely-spaced legs that stroke asynchronously. Researchers found that the flexibility and stiffness of the legs are critical for the shrimp’s efficiency. During the power stroke, the shrimp’s leg is held stiff, maximizing the force it’s able to transfer to the water. But during the forward-moving recovery stroke, the shrimp bends its legs almost horizontal and presses both legs in the pair together tightly. This action minimizes the area of the leg pair and reduces the drag they cause as they move into position for the next stroke. (Image, video, and research credit: N. Tack et al.; via Ars Technica; submitted by Kam-Yung Soh)
https://www.youtube.com/watch?v=hWOtF0RXTwk
A close-up view of the shrimp’s leg as it swims.
January 24, 2023
“Reconfiguring It Out”
Leaves flutter and bend in the breeze, changing their shape in response to the flow. Here, researchers investigate this behavior using flexible disks pulled through water. The more flexible the disk and the faster the flow, the more cup-like the disk’s final shape. Adding tracer particles to the water allows them to visualize the flow behind the disk. Every disk leaves a donut-shaped vortex ring spinning in its wake, but the more reconfigured the disk, the narrower the vortex. This, ultimately, reduces drag on the disk. That’s why trees in heavy winds streamline their branches and leaves; that flexibility lowers the drag the tree’s roots have to anchor against. (Image and video credit: M. Baskaran et al.)
November 23, 2022
Measuring Drag
After a noticeable rise in the prevalence of home runs beginning in 2015, Major League Baseball commissioned a report that found the increase was caused by a small 3% reduction in drag on the league’s baseballs. When such small differences have a big effect on the game, it’s important to be able to measure a baseball’s drag in flight accurately.
In the past, that measurement has often been done in a wind tunnel, but the mounting mechanisms used there result in drag measurements that are a little higher than what’s seen from video tracking in actual games. Now researchers have developed a new free-flight method for measuring a baseball’s drag. The drag measurements from their new method are lower than those for wind-tunnel-mounted baseballs and in better agreement with video-based methods. The authors’ method should be adaptable to other sports like cricket and tennis, which will hopefully provide new insight into the subtleties of their aerodynamics. (Image credit: T. Park; research credit: L. Smith and A. Sciacchitano; via Ars Technica; submitted by Kam-Yung Soh)
June 2, 2022