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A golfer drives a ball into the sunset.

The science of sport

Think "sport" and the words that spring to mind are likely to be fitness, exercise, competition, endurance... and fun; "science" is probably not among them. It's obvious to anyone who loves sport that it's a powerful demonstration of pushing the human body its limits. What's less obvious is that sport is an equally powerful demonstration of science. From the cutting-edge composite materials packed into racing bikes and tennis rackets to the 17th-century maths that bends baseballs through the air, science is the foundation of almost every sport you care to mention. How can Usain Bolt sprint so much faster than you? Is a wooden baseball bat going to make you play better than one made from aluminum? Exactly what's happening to a soccer ball as it curves off your boot, swerves through the sky, and punches into the net? As you'll see in a moment, questions like these have fascinating, scientific answers!

Photo: Golf: You learn to play a game like this by hitting a ball hundreds or thousands of times. Your brain learns to correlate the way you move your muscles with the places where the ball ends up; eventually, after enough practice, you can place the ball wherever you want. In theory, a robot could play just as effectively if you programmed it with the laws of physics, or if you let it practice and learn from its mistakes using a neural network (a type of computer model that learns from experience like a brain). Photo by Eric Tretter courtesy of US Navy and Wikimedia Commons.

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  1. Why do we say sport is scientific?
  2. Hit and run: ball sports
  3. Might as well jump: track and field sports
  4. Feeding your speed: sports that beat the clock
  5. Beating your balance: sports that defy gravity
  6. Find out more

Why do we say sport is scientific?

Science is all about understanding how the world works using theories tested through experiments. At first sight, sport appears to be something different: training hard to beat an opponent (another person or team, a clock or measuring tape, or maybe just that pesky little voice inside your head that keeps pushing you to do better).

Look into sport a bit more closely and it soon becomes obvious that science plays a big part in it. The human body itself is obviously a scientific miracle that can turn a hearty breakfast into a soccer championship, a record-breaking sprint, or a heavyweight boxing title. But leaving the basic biology to one side, there are many more ways in which sport relies on science. Physics, for example, tells us how far you can hit or throw a ball, but it also explains how fast a swimmer can cut through the water, how a diver can somersault, and even why long jumpers have to move their arms in such a drastic way as they fly through the air. Let's look more closely at the science behind a few different kinds of sports: ball sports (including tennis, soccer, and baseball), track and field (athletics), speed sports (such as cycling and swimming), and sports that defy gravity and balance (gymnastics, BMX and skateboarding).

Hit and run: ball sports

If you've studied physics at school, you'll know that we can use a few relatively simple math equations to predict the parabolic (upside-down U-shape) path of an object flying through the air. The science is called ballistics—and it governs everything from how bullets fire out of rifles to how cricket balls soar through the sky. The basic idea is simple. When you throw or hit a ball upward, you apply a force that makes it accelerate (gaining both a vertical and a horizontal velocity). The vertical (upward) velocity and the horizontal (sideways) velocity are independent of one another, though both are important if you're trying to make a ball go as far as possible. As the ball shoots up, the force of gravity pulls it back down, slowing its vertical velocity to zero (when it reaches the peak of its trajectory) and then accelerating it back toward the ground. It's easy to calculate how long the ball will stay airborne and, using this, you can figure out how far it will travel (its range, in other words) by multiplying the time in the air by the ball's horizontal velocity.

In theory, the way to make a ball travel furthest is to strike it at an angle of 45°; simple math tells us that angle should give the maximum range. In practice, you need to take into account various other factors such as air resistance (which depends on the size and surface texture of the ball and how fast it's going), ball spin, and so on; factor those things in and you'll find the perfect angle can be more or less than 45°, depending on what kind of ball you're hitting and how. If you're hitting a golfball with the wind behind you, for example, you might hit it at a steeper angle. That means it'll stay in the air longer. Although it would normally travel a shorter distance in that case, the wind will carry it further in the same time than if you'd hit it at a shallower angle. Not only that, but the wind speed will be higher further from the ground so you may tap into a higher airflow and gain more distance that way as well. If you're driving into an oncoming wind, you might be better going for a shallower angle than 45°. Although the ball will fly lower, it will have a higher horizontal velocity, giving it more power to overcome the wind and potentially going further. (In practice, for reasons I'm not going to go into, hitting a golfball is more skillful and complex than this and involves factors such as how fast you make the ball spin, the way the angled club face strikes the ball, and so on. I'm talking about theoretical science here, not trying to offer practical golfing lessons.)

A soccer player kicks a ball into the net and scores a goal.

Photo: Scoring a goal: sheer skill or cunning physics? Your brain calculates the trajectory of the ball and figures out how to kick it to reach a particular spot. If there are people in the way, you might spin the ball so it curves through the air and bends around them. Skillful players learn how to do this by trial and error, but a scientist could also figure out how to achieve the same effect using the laws of aerodynamics. Photo by Gary Nichols courtesy of US Navy.

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Energy transfer

When you try to hit or kick a ball as hard as you can, what you're attempting to do, in scientific terms, is transfer as much kinetic energy from your body to the ball as possible. In a sport where you use a bat, the bat serves as a go-between in the process, helping you to transfer energy more efficiently.

One of the really interesting things about ball sports is the wide range of different bats and balls that are used; although the basic dimensions of the bat and ball may be specified in the rules of a particular sport, you can still find huge variety. Bats come in all shapes and sizes, in woods of various kinds, metals such as aluminum, and high-tech composites and carbon fibers; the design of a bat has a huge effect on how a ball with respond, and different bats will give very different results even if you apply exactly the same force. Balls are hugely varied too: everything from perfectly smooth, very hard billiard balls and slightly softer golf balls (with their aerodynamic dimpled surface), through cricket balls and baseballs (with their complex outer stitching patterns called "seams"), and squishy rubber tennis balls, right up to soccer and basketballs and those weird-shaped rugby footballs.

A billiard cue, balls, and table.

Photo: When two billiard balls collide, we can get almost total energy transfer—known as an elastic collision. Photo by Brittany Y. Bateman courtesy of US Air Force.

Hit a hard ball with a hard bat and you're attempting to pull off what physicists call an elastic collision. Confusingly, "elastic collision" doesn't mean there's any elastic involved or anything remotely rubbery or bouncy; it's just a formal, scientific way of saying that all the kinetic energy your bat has before the collision is transferred to the ball (and bat) after the collision. When a billiard ball crashes into a second, identical ball and comes to a sudden stop, knocking the second ball away with almost all the momentum the first ball had originally, that's about as close as we ever get to an elastic collision. The forces involved in collisions like this can be considerable. One of the most basic laws of physics, Isaac Newton's second law of motion, tells us it takes twice the force to accelerate a ball to a certain speed if you do it in half the time. So fast, elastic collisions between hard balls (or hard balls and hard bats) involve more force than slower, gentler collisions between softer balls (or softer balls and softer bats), where the energy is passed from bat to ball over a longer period of time and with less force. (That's why cars are designed to crumple up when they crash: slowing down a collision reduces the forces experienced by the people inside, increasing their chances of survival.)

A baseball pitcher hurls a ball towards a batter, wearing a red shirt, who is just about to hit it.

Photo: Baseball involves a hard wooden or metal bat and a fairly hard ball made of leather and rubber. However, because there is some "give" in the ball, the collision between the bat and the ball is less elastic than in billiards. Photo by Shannon McMillan courtesy of US Marine Corps.

Soccer uses a medium-sized, fairly soft, inflatable ball. Heading involves an inelastic collision in which momentum and energy are transferred imperfectly from your head to the ball. Imagine what kind of soccer boots you'd need to wear if soccer balls were made out of solid wood. According to my quick calculations, a wooden soccer ball would be about nine times heavier, so you'd need to give it nine times more energy to kick it to the same height. If all that energy came from your leg, your leg would need to be moving about three times faster during the kick to have nine times more energy to pass on. You'd need to use nine times more force to kick a stationary wooden ball to the same speed or kick with the same force for nine times longer, neither of which sounds possible. Using so much force to kick the ball would tire the players very quickly and make the game much less interesting.

A soccer player kicks a ball on a pitch in Tonga.

Photo: Kicking or heading a soccer ball involves an inelastic collision with your body. Photo by Kristopher Radder courtesy of US Navy and Wikimedia Commons.

Hitting a hard leather cricket ball with a hard wooden bat is somewhat less elastic than a collision between two billiard balls because the ball and the bat do bend and deform slightly during the collision (which wastes a certain amount of energy), and, for various other reasons, energy isn't perfectly transferred. In sports that involve hard balls, you generally have to hit the ball pretty hard to get it to move quickly, because it's fairly dense and heavy. (Again, Newton's second law of motion tells us that you need a bigger force to accelerate a heavy ball than a lighter one.)

Animation showing how a ball deforms as it bounces.

Animation: A soft ball deforms as it hits a hard surface. The materials the ball is made from squash and compress, and the air inside is also compressed, exerting a pressure that makes the ball quickly return to shape. Although this process looks completely reversible, some energy is always lost, which is why a bouncing ball can never return to exactly the same height from which it originally fell.

Not all sports use hard bats and balls. In some sports, we use part of the human body (our arms or legs) or a softer instrument (maybe a tennis racket) to accelerate a lighter and softer ball that's typically filled with air or some elastic material. Kick a soccer ball and what happens is very different to what goes on when you whack a golfball with an iron club. What we get is a much more inelastic collision where the ball initially deforms and squashes inward as you kick or hit it, then springs back to shape and pushes away from your foot. In collisions like this, kinetic energy isn't conserved: the ball and your body have less energy after the collision than your body had beforehand. Balls like this are generally much lighter and (fortunately) we don't need to hit or kick them quite so hard to accelerate them to high speed.

Bar chart showing the range of kinetic energies in sports balls.

Chart: Which sports balls have most energy? We can figure out the kinetic energy of a ball with the formula ½mv2. Plugging in the masses and (higher-end) speeds, we get these sorts of estimates. I would have guessed that golf balls had most energy because they seem to be going so fast, but they're also very light. Soccer balls, kicked hard, have surprisingly high energy because they go faster than you think and weigh almost 10 times more than golf balls. Which balls hurt most when they hit you? Generally, harder and smaller balls (golf balls) because they dissipate their energy very quickly over a small area, which means they exert more force and pressure on your body. That's also the idea behind bullets, except they're pointed to move faster and help penetrate your body. Interestingly, if you check out the similar chart I drew in my bullets article, you'll find modest handgun bullets have comparable energy to fast-moving sports balls (hundreds of joules).

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How do bats work?

A tennis racket hits a ball into the air with motion blur.

Why use a bat at all? Why not just play tennis, cricket, or baseball with your arm and hand the way you kick a soccer ball with your feet? Two reasons for using a bat are obvious. First, it can obviously be made bigger than your hand, so it's easier to connect with a faster ball, which makes the game more fun and more competitive. Second, a bat is less fragile than the human body so you're less likely to hurt or tire yourself. A cricket player might, conceivably, have to bat a ball hundreds of times during a match and play matches like that week after week, year after year. The human hand contains 27 relatively delicate bones; imagine what would happen if it got the kind of beating a cricket bat gets!

The other reason for using a bat is much more subtle and interesting: it helps you to transfer energy from your body to the ball. The design of the bat (how long and wide it is, whether it's solid or hollow, whether the weight is distributed closer to the handle or the batting end, and so on) makes all the difference to how efficiently the energy is transferred. For example, a solid wooden baseball bat will have more momentum (because of its heavier mass) than an identical sized but hollow aluminum bat moving at the same speed, so if you connect with the ball, you should pass on more energy. Then again, if the bat is lighter, you can move it into position more quickly and swing it faster, so its higher speed should compensate for its lighter weight in helping you to pass on your momentum. Which factor is most important? That depends partly on your batting style and personal preference—and partly on the build of your body.

A tennis racket, seen from the side, hits a ball into the air with motion blur.

In his excellent book Physics of Baseball and Softball, Rod Cross explains that you get very effective energy transfer from your arm to a ball when a bat is about six times heavier than a ball and six times lighter than your arm or arms (typical of baseball bats and tennis rackets). You need to have roughly the same ratio in each case (arms to bat, bat to ball) so if you had heavier and more muscular arms, you might be better using a heavier bat than a lighter one. If you're fairly muscular and you're trying to hit a heavy ball, there's no point trying to do it with a bat that's too light, because it won't pass on the energy and momentum from your arms efficiently. Similarly, if you have thin weedy arms (like me), a lighter bat might prove more effective.

Playing area and surface

Different ball sports are played on different surfaces—and over different sized areas—and that also plays a big part in the balls we use and how they're designed. One reason is because balls made from different materials bounce to different heights, even on the same surface; the same ball also bounces very differently on different materials. You might have noticed how tennis players often specialize in playing on a particular surface such as clay, asphalt, or grass; each of these affects the speed and bounce of the ball in a radically different way, with softer clay absorbing more of the ball's energy and effectively slowing down the strokes, and grass speeding them up.

A table tennis match.

Photo: Why is table tennis so fast and furious? Consider the science. The bat, ball, and playing surface are all hard, so the collisions are elastic and fast. The ball is small and light, so it accelerates quickly. The table is very small, so the fast-moving ball travels very quickly from one end to the other. Imagine if the ball was bigger and softer, the table was made of very soft rubber, and the bat was more like a tennis racket. That would make the game much slower and far less interesting. Photo by Anton Wendler courtesy of US Navy and DVIDS.

There's no reason why we couldn't play golf on a table top with clubs the size of pencils and balls made of cotton—but it wouldn't be a very interesting or challenging game. Golf is a game people like to play outdoors over long ranges and that decrees the type of ball needed to play it. The ball has to travel a relatively long way (at least in the initial "drive"), so it has to be small to reduce air resistance. (The dimples on a golf ball help it to travel further by reducing the drag even more.) To stop it from being deflected too much by the wind, it has to be relatively dense and heavy—and that means the thing you hit it with (the club) has to be dense and heavy too (made from wood, metal, or carbon fiber, golf clubs have a thin shaft and a heavy weight at the end where they contact the ball).

Ball skills

Different people can achieve very different effects with the same bat and ball. Tennis is a subtle game that can be played in many different ways, but one of its key features is the serve: the fast, powerful opening shot. Taller players with longer arms naturally have an advantage here: the taller you are and the higher you reach, the faster the tip of your racket is traveling when it hits the ball (because the velocity of any point on a rotating wheel is greater as its distance from the point of rotation increases) and (in theory) the faster the ball will go when it blasts toward your opponent.

A man launches a red ball down a ten-pin bowling alley toward skittles.

Photo: When you bowl, your brain instantly works out how to control your muscles to throw the ball to reach a precise position in space. On paper, that's simple physics, but it's amazing that our brains and bodies can do things like this instinctively, with no calculations at all. Photo by Jon Dasbach courtesy of US Navy and Wikimedia Commons.

What do world-class footballers, cricket and tennis players, baseball champs, and even billiard players have in common? An instinctive ability to put a ball precisely where they want it to go, and often where their opponent least expects it. That doesn't just mean being able to hit or kick a ball as far as possible, but using things like spin to make it curve to one side. Spinning balls bend because of science—usually through something called the Magnus effect: as a ball spins, it changes the way air moves around it, speeding it up on one side and stopping it on the other, producing a force that pushes the ball in an unexpected direction. Balls with seams and cricket balls that have been polished on one side curve through as they fly because they make the air more turbulent on one side than the other.

It's much easier to see these things demonstrated in videos and animations than to read about them. Derek Muller of Veritasium and Australian physics professor and sports-physics expert Rod Cross have made two great YouTube videos showing how these effects occur: the first is a simple demonstration of how the Magnus effect makes a ball curve; the second explains the physics of balls with seams.

Might as well jump: track and field sports

Track and field sports are contests in which each individual athlete pits their body against other people's bodies; attempting to run faster, jump higher, or throw further is the name of the game. Although much of athletics is about harnessing the biology of the body—using the strength of individual muscle groups, for example—there's a lot of science going on outside the body too. Who'd guess that a long jumper or a pole vaulter is secretly harnessing the power of physics?

Long jump

You might think the long jump it's simply a matter of running fast, hurling yourself into the air, and hoping for the best. Not if you want to win a gold medal! As a jumper, what you want to achieve is to land your legs as far forward as possible (in front of your body), but you can't possibly take off with them in that position: they have to be pushing backward (behind your body) to launch you into the air. So what you have to do is radically alter the position of your legs while you're in midair. Now once you're airborne, if you move either your arms or your legs away from your torso, your body will rotate about your center of gravity (the point on your body where all your mass seems to be concentrated). Moving either your arms or your legs nearer to or further from your body will change your moment of inertia (the distribution of your mass about your center of gravity). It's a basic law of physics that your angular momentum (the momentum your body has because it's rotating) cannot increase or decrease (angular momentum is "conserved," as physicists say). If you want to throw your legs forward and outward, the way to do it is to throw your arms upward, then bring them down quickly. Then, as your arms shoot back, your legs shoot forward to compensate. It's a bit like when you're swimming and you want to stand up: if you bring your arms down quickly in front of you, your legs shoot down beneath you to ensure the conservation of angular momentum. Almost the same move happens mid-air in the long jump.

A long jumper flies through the air toward the sand in the pit.

Photo: Long jump is all about conservation of energy and momentum. Once you're airborne, there's no way to get any more energy, so the run-up is crucial: the more kinetic energy you give you body the further you'll go. In midair, you can move your legs further forward by bringing your arms around and back, as this jumper is just about to do. There's a wonderful photo of the sequence of movements a long jumper goes through in Anatomy of an Athlete, The Sydney Morning Herald, 2016. Photo by Matthew A. Ebarb courtesy of US Navy and Wikimedia Commons.

Pole vault

Pole vaulting is another example of a sport where physics can give you a hidden hand. Pole vaulting is a bit like a super-high high jump where you use a long, bendy, carbon-fiber pole to throw yourself over a bar. Just like long jump, it looks simpler and less scientific than it really is. And just as long jump is all about the conservation of angular momentum, so pole vaulting is about the conservation of energy.

Consider what happens during a pole vault: you start off running toward the bar with the pole in your hands. After you've picked up speed, you have a fair bit of kinetic energy (energy of movement because you have both mass and speed). To lift your body a certain distance in the air, you need to give it a certain amount of potential energy. The pole helps you convert horizontal into vertical motion, and it does so by converting your kinetic energy into potential energy. After you've reached the end of your run-up, you stick the pole into the ground. Your momentum and energy is now transferred into the pole, which bends into a curve and converts your kinetic energy into elastic potential energy, slowing you down in the process. Being elastic, the pole quickly springs back to its original shape, straightening out and lifting you upward, and converting its elastic potential energy into kinetic energy and gravitational potential energy (the energy your body has when it's up in the air). Ideally, all of the kinetic energy you had in the run-up is converted into potential energy when your body reaches its highest point and stops climbing. That explains why the run-up is so crucial to a pole-vaulter: if you don't run at top speed, and plant your pole correctly or hold it firmly, your kinetic energy won't be completely converted to potential energy and you won't gain as much height.

How a pole vault is based on the law of conservation of energy.

Artwork: Pole vault is a good example of the conservation of energy. 1) During the run-up, your body tries to gain as much kinetic energy as possible. This is vital because, once you're airborne, there's no way to gain extra energy. 2) When you stick the pole into the ground, it bends and converts your kinetic energy into elastic potential energy. 3) As the pole straightens, it gives the kinetic energy back to your body. The pole's job is to help you convert kinetic energy (your running energy) into potential energy (the energy you have when you climb into the air) and horizontal motion into vertical motion. 4) When you let go of the pole, you're climbing upward, working against the force of gravity. Your body's kinetic energy is gradually converted to potential energy as you climb, which is why you start to slow down. 5) At your highest point, as you cross the bar, your body has maximum potential energy. All the energy you have at this point came from the kinetic energy of your original run-up.

The sequence of moves involved in the pole vault.

Photo: Here's the actual sequence of moves in the pole vault. These are photos of Cale Simmons competing in the men's pole vault finals at the US Olympic Team Track and Field Trials in 2016. Photos by Tom "Drac" Williams courtesy of US Air Force and DVIDS.


Physics is even at work in the simplest sport of all—running—and it can help us understand why a super-star like Usain Bolt can run so much faster than the rest of us. According to Newton's second law of motion, you can make a mass accelerate (gain speed) by applying a force to it. We can describe the same law in a slightly different way: you can give something more momentum by applying a force to it for a certain amount of time (with what's called an impulse). If you're a world-class sprinter, what makes you run faster is your ability to deliver impulses with your legs that accelerate you faster. But the more massive you are, the more force you need to accelerate. If you have huge muscular legs, you'll need more force to pick them up and put them down and keep your body moving quickly. In the case of Usain Bolt, a very large and tall man, his ability to generate powerful impulses with his legs (to gain acceleration) outweighs his considerable mass (which needs more force to accelerate it). And that's why he's so fast.

Feeding your speed: sports that beat the clock

Cycling, swimming, skiing, and bobsleigh are all about beating the clock—but they're also about beating another type of science called fluid dynamics, which is the physics of how liquids and gases (fluids) move around objects (or how moving objects slice through fluids, which is exactly the same thing). Have you noticed how Olympic swimmers wear those super-streamlined body suits and cyclists put on teardrop-shamed helmets and crouch over their bikes? The reason is the same in both cases: the swimmers are trying to minimize the resistance their body offers to relatively dense, liquid water, while cyclists (who move quite a bit faster) are attempting to reduce air resistance (drag) by making their bodies more aerodynamic. Most of us don't notice air resistance because we never really go fast enough; when you're walking, gravity is the force that causes you most bother. You certainly notice the force of air resistance on a cycle—and it's very obvious if you speed along in a car with the windows or the roof down.

Photo of a speed cyclist wearing a helmet.

Photo: Aerodynamics is as important to cyclists as it is to designers of race cars and jet planes, which is why they wear tight clothes and lean forward like this. Although you can't see it in this photo, racing cyclists also use special handlebars that position their elbows much closer to their torsos, significantly reducing drag.

Drag is even more of a problem for swimmers because water is so much more dense than air. It's much easier to swim (horizontally) through water than to walk through it (vertically) because your body assumes a tube-like shape that can move forward by pushing less water out of the way (it has what we call less form drag because it presents less of an obstacle to the water trying to move past it). Those streamlined suits you see swimmers wearing work in two very interesting scientific ways—one involving biology, the other physics. The biological effect is achieved with tight-stitching throughout the suit that compresses the swimmer's muscles so they work more efficiently, producing less fatigue. The physical effect comes from the texture of the suit. There are tiny V-shaped ridges on the surface designed like the dermal denticles (placoid scales) on a shark's skin. These help to reduce friction drag (the resistance between your body and the layers of water sliding past it) by creating tiny vortices, reducing the water's tendency to become turbulent as it flows past your skin. If you're doing a speed sport, understanding how to minimize form drag and friction drag is the way to go faster, but it's also the way to go further. Pushing against the air or the water wastes energy, and there's only so much of that available to your body. The more efficiently you use your limited energy supply (the further you go with each stroke or your arms or push of your legs), the longer you can go without getting tired.

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Beating your balance: sports that defy gravity

If you're a tennis or golf player, your brain has an intuitive understanding of ballistics: you know exactly where a ball will go when you hit it. If you're a cyclist or a swimmer, you learn about fluid dynamics very quickly. On the track or field, you soon master force, energy, and acceleration even if you don't actually think about them scientifically. What about sports like skateboarding and BMX? What science do they involve?

Skating skills

Skating is a supreme demonstration of physics. Even the most basic move of all—kicking against the curb to get yourself moving in the first place—is an example of Newton's third law of motion: you kick back against the curb to make your body and the board go forward. Pull off a cool stunt in mid-air and you're nothing less than a mini Albert Einstein: you're instinctively harnessing the power of physics to maintain your balance, which we can define as the way your body keeps itself upright despite gravity's pesky determination to pull it to the ground. The general approach to skating is to bend your knees and stand in a kind of flexed position. Why? The lower you stand, the lower your center of gravity and the easier it is to keep your balance (bending your knees also helps to absorb impacts when you land and reduces the shock to your legs and spine).

A skateboarder jumps over a staircase.

Photo: Skateboarders master physics instinctively: skating is all about center-of-gravity, Newton's laws, conservation of energy, and conservation of angular momentum. In this trick, widely spread arms give better balance by increasing the skater's moment of inertia. Photo by Natasha Stannard courtesy of US Air Force and DVIDS.

If you pull a trick where you shoot off a ramp and lift your legs off the board, so your body and your board briefly separate, travel independently for a time, then come together again when you put your feet back down, you're making use of inertia: as Newton's first law of motion tells us, objects either stay still or keep moving at a steady speed unless a force acts on them. Even though your body and your board part company for a few seconds, both keep moving in a predictable way because of their inertia, and that allows you to reconnect with your board again further down the line.

Skaters put their arms out to balance their bodies. Why? For the same reason that a tightrope walker often holds a long, heavy pole. If you're trying to keep your balance on a skateboard, you're trying to stop your body from rotating. If you're on the ground, and your center-of-gravity is too far to one side (not directly over the board), the top of your body will tend to rotate about your feet: in physics terms, your body will experience a moment that will make it turn— in other words, you'll fall over! A lower center-of-gravity is one way to make balancing easier; a higher moment of inertia is another way. What that means is arranging your body so some of its mass is further from the point of rotation (in other words, you put your arms out). You'll have noticed how ice skaters can slow down their spinning moves by putting their arms out, and speed themselves up by bringing their arms in; since their angular momentum has to stay constant, bringing their arms in (reducing their moment of inertia) means their angular velocity has to increase, so they spin faster. When you're skateboarding, if your arms are outstretched and you start to lose balance, your body will rotate more slowly, so you'll have more time to compensate. Instinctively, you'll shift the position of your arms to cancel the rotation of your body, balancing yourself once more. A top skater has an instinctive ability to control his or her angular momentum—like a kind of human gyroscope!

Diving for gold

Swimmer about to dive from the pool side into the water

Photo: Diving is all about mastering momentum: converting linear momentum to angular momentum and conserving angular momentum as you spin. Photo by R. Jason Brunson courtesy of US Navy.

Sports that involve precise rotations of your body, such as diving, are all about mastering the conservation of angular momentum. You'll have noticed how divers tuck their arms and legs in after they spring off from the board, rotate a couple of times in a somersault, then extend their limbs to enter the water cleanly and safely. Why spring off the board? It's much the same as the pole vault: the energy you put into the board by jumping down on it is temporarily stored inside the bent wood as elastic potential energy. The elasticity of the board makes it spring upward and gives your body first kinetic energy, then potential energy. As you tuck your limbs in and start the dive, your body starts to rotate so your linear momentum (your movement straight upward) is converted into angular momentum (spinning motion). Once you're diving, the conservation of angular momentum comes into play. With your arms and legs tucked tight to your body, your moment of inertia is as small as it can possibly be so you spin at your fastest speed. By extending your arms and legs, you increase your moment of inertia, slowing down and then cancelling your rotation so your body enters the water vertically, ideally without rotating.

Sport + science = win

Some people are born sports players and some aren't—and no amount of science will turn a clumsy person like me into a world-class athlete. Many sporting stars understand instinctively how to be the best in their field—and that built-in understanding, gained through years of practice by trial and error, can achieve the same or better results as a theoretical, scientific approach and by totally different means. When Usain Bolt sprints for the line, the last thing he's doing is calculating how much force his legs can turn into acceleration through Newton's laws of motion. But understanding a little bit of the science behind your favorite sport can help you harness your natural abilities and achieve more; it can help you run faster, swim further, or pull off neater skating tricks. I'm not suggesting for one moment that success in sport is purely about science: many other factors, including physical ability, natural talent, endurance, courage, and determination are at least as important (and sometimes much more so). Does science take the fun out of sport? Not a bit of it: it adds an extra level to our understanding and helps us appreciate our amazing sports stars even more!

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Woodford, Chris. (2012/2023) The science of sport. Retrieved from [Accessed (Insert date here)]


@misc{woodford_2FA, author = "Woodford, Chris", title = "The science of sport", publisher = "Explain that Stuff", year = "2012", url = "", urldate = "2023-06-29" }

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