After a year-long delay (and what a year it was!), the Tokyo Olympics are here finally here. For two weeks, the world’s best athletes will put on incredible displays or skill, fortitude, stamina, and physics. Yes, physics.
To be the very best, athletes break down their sport to a science. Momentum is translated to joules, runners understand the intricacies of different muscle fibers, kayakers deftly navigate the math behind fluid dynamics. Here we break down some of the interesting science that’ll be on display in the next two weeks.
Swimming Like a Fish
Much has been written about the superhuman athletic ability of swimmer Michael Phelps. He’s a genetic wonder, built like a fish, with hands and feet like canoe paddles. All this is true—it is impossible to win at the Olympics without a genetic predisposition to your sport. Team USA at the Tokyo 2020 Olympic Games will be hoping to surpass—or at the very least imitate—what made Phelps a swimming phenomenon.
Body: Phelps’s body is a famously specialized swimming machine. His wingspan, at 6 ft. 7 in., is 3 in. longer than his height. And his long torso and relatively short legs—he has an inseam of 32 in.—let him ride high in the water.
Biochemistry: Strokes such as the butterfly tend to build up lactic acid in muscles, reducing their ability to perform. Phelps’s exact numbers are kept secret, but tests suggest that he naturally produces far less lactate than most athletes do.
Flexibility: Some sports require strength (shot put); others, flexibility (gymnastics). Swimming requires both. Phelps’s flexible elbows, knees, and ankles allow him to move through water with minimal resistance.
Hydrodynamics: In a 200-meter freestyle race, a swimmer moving at 3.8 mph expends 290 kilojoules fighting his own drag. To combat this, Phelps adopted a streamlined swimming posture—head down, hips high.
Technique: Phelps was the master of the dolphin kick. By pushing off the wall and whipping his legs, he can swim faster than with a traditional stroke—gaining an advantage of half a body length over competing swimmers.
Training: Phelps trained every day of the year—4 hours in the pool, 1 hour on dry land. Since swimmers can burn about 1,000 calories per hour, Phelps’s diet tended to be relatively high in carbohydrates to avoid glycogen depletion.
At the 2008 Beijing games, Michael Phelps was in a dead heat with Serbian Milorad Čavić. Čavić appeared to touch the wall first, but Phelps was the first to exert the 6.6 pounds of pressure required to activate the touchpad. The result: a victory margin for Phelps of 0.01 second, which the Serbian team disputed. But a review down to 0.0001 second confirmed Phelps’s gold.
In other words, timing is everything.
Marathoners vs. Sprinters: A Science Breakdown
Marathoners: Distance running is all about aerobic efficiency, and most marathoners’ oxygen absorption (VO2 max) is almost twice that of an average person. Elite marathoners’ muscles are largely composed of slow-twitch fibers, which maximize oxygen use for muscle stamina.
Sprinters: A 100-meter race is over before aerobic efficiency becomes a factor, so a sprinter’s oxygen absorption rate is less important than fast muscles. Sprinters can have up to 80 percent fast-twitch muscle fibers, which contract up to 10 times faster than slow-twitch fibers.
The Giant Swing
When gymnasts make the grand, sweeping arcs of the giant swing, it may look like a simple series of circles. But there is a complex interchange of force and energy between the gymnast and the flexible bar she’s holding onto. The giant swing must be both artful and functional—gymnasts must maintain good form, keeping their arms straight and toes pointed, while building up enough momentum to launch into a double-somersault dismount. With great strength and incredible timing, these athletes gracefully defy gravity.
- The gymnast begins in a handstand position above the rail. Her legs are straight, toes pointed skyward.
- As she drops from the handstand, friction between her hands and the rail slightly reduces rotational velocity, which approaches 275 degrees per second during the first half of her maneuver. To compensate, the gymnast begins a “tap”—first by dropping her legs and bending slightly at the waist to avoid the lower rail.
- Just before reaching vertical, the gymnast arches her back to increase rotational energy. Down-force at the bottom of the swing can approach 4 to 7 g’s and flex the rail as much as 4.5 in. off center.
- She completes the tap on the upswing by flexing hips, pelvis and stomach and swinging her legs forward to pull her center of gravity closer to her center of rotation. This uses angular momentum to boost angular velocity—304 degrees per second.
- The dismount release window lasts 67 ms, when the gymnast’s body is between 10 degrees above and 20 degrees below horizontal. Flight time is less than 1.5 seconds.
💡 The Rebound: A gymnast transfers energy to the highly flexible fiberglass rail during her down-swing, which she reabsorbs in the upswing to increase rotational velocity.
The Hydration Race
An Olympic athlete consumes as much as 3 gallons of water per day during competition (that’s 5.5 times the suggested intake for a typical person). Losing just 2 percent of body fluids (that’s about 3.5 pounds or 2 quarts in a 180-pound athlete) is enough to cause a dip in performance. “When you lose water, your blood gets thicker and your heart has to work harder to pump it,” explains sports nutritionist Nancy Clark. Knowing sweat rates allows an athlete to properly rehydrate to prepare for the next round or match.
Raising the Bar
The secret to high vaults is 85 percent physics, 15 percent acrobatics. To build up enough kinetic energy to lift themselves within striking distance, athletes needs to run fast — at least 33 ft./second. When the pole is planted, it acts as a spring to transfer an athletes energy, around 4000 joules, from the horizontal plane to the vertical. The additional three to four feet comes from bending the body and pushing the athlete’s center of gravity up and over the bar.
- Approach: The faster a vaulter sprints down the runway, the more energy he transfers to the pole when he plants it in the box. Ideally, the athlete reaches top speed in no more than 10 or 12 strides.
- Plant: Entering the box at an 18-degree angle, the vaulting pole should bend about 70 percent of its original height, or between 120 and 160 degrees, depending on the vaulter’s height and momentum.
- Takeoff: The potential energy in the bent pole is transferred back to the athlete’s body as kinetic energy. The vaulter jumps high into the air and pulls himself into a handstand as the pole starts to straighten.
- Over the top: Flying through the air, the vaulter contorts his body so that he’s facing the crossbar. Vaulters use gymnastics training—such as tucking, rolling, and handstands—to help master this maneuver.
Inside the Vault Bar: Specifically designed for the user’s weight and height, modern vaulting poles are made of three layers of fiberglass and/or carbon-fiber cloth impregnated with resin. When heated, the combination forms a lightweight composite. The outer layer determines stiffness, while the two inner layers are for strength and flexibility.
The Anatomy of a Dive
Olympic divers dazzle with their acrobatics in the air, but it’s the launch off the board that spells the difference between a medal-winning dive and a splashy failure. During the approach, the diver takes a few short, brisk steps to build momentum. The diver’s hurdle jump occurs 12 in. from the board tip. A high jump contributes to board depression on the descent and builds up mechanical force (about 5000 newtons). The takeoff gains power as the board recoils, projecting the diver up at 12.3 mph as the athlete reaches a height of at least 18 ft. above the water. This gives the diver a flight time of up to 1.5 seconds, as well as the rotational force needed for the maneuver.
💡 A diver must drop 1.4 ft. from the peak of a hurdle jump to load the board with energy that will propel him or her into a three-and-a-half-rotation somersault.
The Genius Behind Kayak Physics
Kayaking rapids take “strength, balance and focus,” says three-time Olympian Scott Shipley. Competitors must navigate 18 to 25 gates suspended above water flowing at about 15 ft./second. The toughest part of the race is an upstream gate, where reversing currents can turn a small mistake into a race-ending rollover.
Shown above, rocks, boulders or ledges can disrupt the flow of a river, creating eddies—pools of calmer water that form behind the obstruction. In an eddy, the current changes direction and curls upstream. Here’s how an athlete navigates this fluid physics during kayak slalom racing.