Wildly Spectacular Sports Science
Chapter One: Bat and Ball Sports
What better place to start a book on sports than with America’s national pastime, baseball (and its close relatives, softball and Wiffle ball)? We’re in “it’s outta here!” territory—or was that “swing and a miss”? Either way, there’s a lot of science at work, particularly if you’re trying to figure out why one pitch will let you tee off while another will curve and drop right past you into the catcher’s mitt.
You will likely see some of the scientific principles behind these sports cropping up again later in the book, in slightly different forms. But it’s good to get started “right off the bat” by matching that science with sports you’ve probably played for as long as you can remember. That way, you might find that you don’t have to deal with so many knuckleballs . . . but we can’t promise.
Time Factor: 5 minutes
How Does a Knuckleball Work?
You’re at the plate, hands gripping the bat and eyes on the ball as the pitcher delivers. You’ve got enough time to line up this meatball to send it flying, and you power into your swing. But a split second before you make contact, the ball dips to the left—five inches beneath your bat. Strike one! Two more pitches and two more swinging strikes follow. You’ve just been caught by the most devilish pitch in baseball: the knuckleball. Curveballs curve, sinkers sink, and fastballs go fast . . . but knuckleballs just can’t be predicted. They seem to dip, wiggle, and stall, and no two pitches behave the same way. Plus, they’re slower than a herd of snails stampeding through peanut butter. So what’s the story?
It’s No Drag
Baseball isn’t the only sport featuring a ball with a mind of its own. Volleyball spikes and bowled cricket balls can outfox opponents because of their erratic movement. Cristiano Ronaldo, star forward for Real Madrid soccer club, regularly sends free kicks zigging and zagging past walls of defenders and into the net. The name he gives to this no-spin weapon? “The knuckleball.” Scientists have gained a basic understanding of the knuckleball—a lack of spin makes its flight unpredictable. But why that happens is still a matter of study in physics labs. You can do a simple experiment to get an idea of just what makes the knuckleball such a devious pitch, all in the comfort of your kitchen.
★ Empty 2-liter soda bottle (must be clear)
★ 10 marbles
★ Paper towel
★ Funnel (optional)
1. Fill the bottle to the very top with water and place it on a table or counter.
2. Find a position, crouched or sitting, where you can observe the bottle comfortably at eye level.
3. Hold a marble, pinched between forefinger and thumb, directly over the mouth of the bottle. The marble should almost touch the water.
4. Release the marble, making sure that you don’t let it spin out of your hand.
5. Observe the marble’s path as it sinks.
6. Repeat Steps 3 to 5 with the other marbles. Can you get three in a row to go the same way?
Make sure the water level is right up to the top of the bottle throughout the experiment. That way, the marble won’t pick up any spin as it drops throu gh the air into the water. Top up the level if it gets low and wipe the side of the bottle with the paper towel.
In this experiment, you’re observing a basic scientific principle: Many forces behave similarly in gases and liquids. A knuckleball’s flight through the air (a gas) is similar to the marble’s path through the water (a liquid). You can see that no two “drops” were identical, just as no two knuckleball pitches are. A spinning ball (in curveballs, fastballs, and other pitches) channels air to one side. That channeling creates a consistent wake behind the ball, making the drag—the force that slows its forward movement—behave steadily. Without the spin, the knuckleball channels air this way and that depending on tiny variations in its movement. There’s no consistent guidance, so the ball goes haywire. Sometimes it might even go where you expect it to—but don’t count on it, slugger.
Time Factor: 45 minutes
Why do Pitchers Raise a Leg So High?
“He-e-e-re's the windup . . . and the pitch . . . STEE-RIKE THREE!”
Whether it’s Game 7 of the World Series or opening day of Little League season, those words describe some of the most suspenseful and dramatic moments in a baseball game. What makes it even more exciting is watching the pitcher lean way back, with his front leg stretched out and up, before unleashing that heat-seeking fastball. You might not have realized that with each delivery, the pitcher is performing a science demo of the principle known as torque. And that torque feeds into momentum, the force an object has when it moves—an object like a 95 mph fastball, for instance.
Prepare to transport from the world of Major League fastballs to medieval fireballs. You’re about to test a mechanical throwing arm by building a miniature trebuchet, the sort of throwing machine that terrified castle defenders. Back in the Middle Ages, soldiers attacked fortresses by heaving stones, dead or diseased animals, and even blazing fireballs over the walls. It took a lot of force to launch those heavy objects over great distances, and this experiment will show you how the attackers could maximize their force. Real trebuchets were about 30 feet tall and could launch a 300-pound rock about 300 yards—hey, don’t get any crazy ideas!—but your smaller version works on the very same principles of torque and momentum, shedding light on how that outstretched leg helps a pitcher.
★ Firm cardboard (from a heavy box)
★ Sharp pencil
★ 2 strong rubber bands
★ Masking tape
★ Plastic spoon
★ Ping-Pong ball or scrunched-up tissue paper
1. Measure and cut out two pieces of cardboard—one 6 × 6 inches (the “base”) and the other 2 × 6 inches (the “launcher”).
2. Fold the launcher piece in half, so that each half measures 2 × 3 inches.
3. Use the pencil to punch a hole in the middle of each flap of the launcher.
4. Line up the folded edge of the launcher with one edge of the base, at center.
5. Mark and then punch a hole in the base, directly under the holes of the launcher.
6. Cut one rubber band and tie a knot in one end.
7. Feed the other end of the rubber band from below the base and through the two launcher holes. (The launcher should still be lined up along the edge of the base, with the flaps facing inward.)
8. Tie the other end of the rubber band so that there’s just over an inch of slack between the two knots.
9. Glue the underside of the launcher onto the baseand tape it with two pieces of masking tape as well.
10. Unfold the launcher and tape the spoon onto it. The spoon will need to move with the launcher acting as a hinge, so make sure you leave a little space for the launcher to move freely.
11. Now you’re ready to fire. Holding the base firmly, pull the spoon back, load it with the Ping-Pong ball (or balled-up tissue paper), and fire.
12. Try a few firings to get an average distance, then cut and remove the rubber band.
13. Cut, knot, and feed the second band through (as you did in Steps 6 to 8), but this time leaving a shorter gap between the knots.
14. Try some sample firings and compare the distances.
You might find it easier to have a friend hold the base down while you load up and fire. And remember: no blazing fireballs!
During a windup, a pitcher’s body-twist and leg-raise build up force, transferring energy to their throwing arm. When the leg starts to swing down, it transfers force into the pitcher’s upper body and arm. By then it becomes a matter of increased momentum, which is the force of movement.
By tightening the rubber band in this experiment, you’ve loaded a lot more force into the trebuchet’s throwing arm (the spoon), just as the leg kick adds more force into the pitcher’s delivery. Isaac Newton
gave us the law that force is made up of mass × acceleration (speed), or F = m × a . The pitcher’s windup, like the tightening band, is increasing the
overall force (F). So, since you’ve increased the force, and the mass of the baseball or Ping-Pong ball remains the same, then the acceleration must go up, too. More speed means longer tosses of fireballs . . . and faster fastballs.
Time Factor: 5 minutes
What Happens When a Pitcher “Doctors” a Ball?
Pitchers absolutely love licking their fingers. Is it just a nervous tic? Leftovers from yesterday’s sloppy joe? Or is there more to it? Well, the rules of baseball are clear about what pitchers can and can’t do to a ball, and they always have to wipe any wet fingers on their uniform before throwing. Since the 1920s, it has been illegal to tamper with a ball (called “doctoring”) to get pitches to break wildly and unpredictably. But pitchers have tried all kinds of ways to make a “spitball,” like applying pine tar, grease, or tobacco juice (gross!), and even notching and scuffing the ball. So why risk ejection—and crossing over to the Dark Side—to doctor a ball? And just what happens with a doctored pitch?
Most pitches form a gently curving path as the spinning baseball moves aside the air that it meets. But anything uneven or bumpy on the surface of the ball will affect its flight. A doctored ball begins spinning like a normal
pitch, only the irregularity on its surface creates turbulence as it passes through the air. (Maybe you’ve experienced air turbulence when a plane ride turns bumpy.) This experiment uses a technique similar to that of a wind tunnel. That’s where engineers test automobiles and airplanes to see how they are affected as they move through the air. Wind tunnels do the opposite—they move the air past the car or plane. Here you’ll use rising smoke to show the flow of air and the turbulence caused by an object in its way.
★ Scented burning stick (like incense)
★ Safety matches
★ Pen or pencil
★ An adult
1. Find a spot where you can observe smoke, like next to a solidly colored wall (with no patterns).
2. Have an adult light the scented stick. Or (if no stick is available) light a match and blow it out.
3. Make sure the stick is held still, away from drafts, with the solid wall behind it.
4. Observe the smoke rising straight up and eventually spreading out after it travels a few inches.
5. Hold the end of the pen or pencil in the first couple of inches of rising smoke.
6. Observe what happens to the smoke as it passes.
7. If you’ve used matches instead of a stick, repeat Steps 2 to 6 to get another good look.
Make sure you have an adult dealing with the burning stick and matches. If you can’t find a scented stick, you can get the same effect from the smoke rising from a safety match that has been blown out. Long matches—the ones you use in fireplaces—produce smoke for longer than ordinary safety matches.
The straight movement of a liquid or gas is called a laminar flow. You get a laminar flow with rising smoke, or when you run water from a faucet. When that flow is disrupted, it goes in different directions and becomes a turbulent flow. Sometimes it regroups, but then it goes topsy-turvy again. The main thing to note is the unpredictable nature of the movement. The rising smoke is a laminar flow, but it becomes a turbulent flow when it hits the pencil or pen.
This experiment is a visual display of how a doctored baseball creates turbulence—and unpredictable motion—as it passes through the air on the way to the plate. You can see it swirling, jumping, and coming briefly back to its original path.
Time Factor: 30 minutes
Just What Is the “Sweet Spot”?
It's the very first at bat of softball season, and the perfect pitch is on the way—so you open up your stance, step into the swing, and . . . YOUCH!!! Foul ball. You drop your bat—your hands can’t hold a thing. Was that an electric shock, or what?! Looks like you missed the “sweet spot,” that bit of the bat that feels “right” when you make contact with the ball. And it’s not just softball and baseball bats that have it—tennis and squash rackets, golf clubs, and anything else that hits a ball all have an area that’s just right for making clean contact. It’s all down to elastic matters. “Elastic” isn’t just the rubber band you fling across the classroom, it’s also an important concept in physics.
In physics terms, a ball hitting a bat is known as a collision, or “a meeting of objects in which each exerts a force upon the other, causing the exchange of energy or momentum.” This exchange of energy is the key to the sweet spot. An elastic collision transfers kinetic energy (the energy of movement) during the exchange. The opposite type—an inelastic collision—absorbs some
or all of that kinetic energy and converts it into other types of energy, like heat, sound, or in the unfortunate case of your stinging hands, vibrations. You experienced an inelastic collision by not making contact along the right part of the bat, which is a measly few inches long. That’s the sweet spot: Hits feel good when you make solid contact there (no vibrations) and the kinetic energy can send the ball over the outfield fence. Elastic and inelastic collisions feature in lots of sports. Here’s a chance to test some familiar objects to see how they stack up.
★ Large cardboard box (sides at least 2 square feet)
★ Brick wall or wooden fence
★ Tennis ball
1. Cut the four upright sides of the box to create four rectangles or squares.
2. Stack those four sides and lean the stack (almost upright) against a brick wall or wooden fence.
3. Stand about 10 feet back and throw the ball at half speed at the cardboard stack. Note how far back the ball bounces.
4. Remove one of the pieces of cardboard, restack, and repeat Step 3.
5. Continue until you throw at the one remaining piece.
6. Now throw the ball at the same speed directly at the wall or fence, again observing how far the ball bounces back.
7. Fill the bucket with water and throw the ball into it from 10 feet, observing what happens.
Make sure you peform these tests where you won’t be making a mess or disturbing anyone. You’re throwing the ball at half speed for a reason.
This experiment is a great demonstration of elastic and inelastic collisions. Remember your hands stinging and the softball just skidding off the bat for a foul? Congratulations—you were demonstrating an inelastic collision. The kinetic force of the ball and bat transferred into vibrations that traveled into your hands.
You should be able to judge how elastic or inelastic each of the objects in this experiment is. In particular, what did you learn as you removed the layers of cardboard one by one? How about when the ball landed in the water—was it elastic or inelastic?
Sport: Wiffle ball
Time Factor: 15 minutes
Why Is a Wiffle Ball So Hard to Hit?
Sure, baseball and softball are a blast to play, but Wiffle ball may have them beat. It’s easy to organize (can’t find nine players for each team? No problem!), you can play it pretty much anywhere, and you likely won’t break any windows with your plastic equipment. But a scientific secret lurks behind the scenes. We all know that it’s really hard to hit the ball. Okay, so the yellow bat is half the width of a Louisville Slugger and the ball is coming at you at about 40 mph, less than half the speed of the “chin music” that major leaguers face every day. But the difficulty seems to come from the crazy flight of the ball once it’s pitched. Forget about a pitchers’ duel—we’re talking a pitcher being cruel!
The key to a nasty Wiffle ball pitch lies in science—a special branch of physics, in fact, called fluid dynamics. It’s all about the mechanics of fluids and the forces that act on them. But here’s something to remember: “Fluids” don’t just mean liquids; they also include gases. So when we talk about a Wiffle ball’s path through the air (which is a gas), we’re really talking about its path through a fluid. Some of the turns and dips in a Wiffle ball’s path are the same as those of a baseball or soccer ball traveling through the air. But it’s those holes in the ball—and the movement of the air inside them—that make all the difference, as you’ll see with this simple demonstration.
★ Duct tape
★ Wiffle ball
★ Friend to help you
1. Cut two long pieces of duct tape and wrap them around the ball so that all of the holes are covered.
2. Ask a friend to be the catcher, about 15 paces from you.
3. Throw 10 pitches—some of them curveballs (flicking your throwing hand right or left on delivering).
4. Judge how easy it was for you to control the pitches and for the catcher to track them.
5. Now remove the tape to expose the holes.
6. Repeat Steps 3 and 4.
7. The second batch of pitches should show a lot more movement.
Conduct this experiment outside where you have a bit of space.
Let’s start with the taped-up Wiffle ball, which is acting more like a “normal” ball. Two elements come into play. First: As it flies through the air, the ball usually spins, triggering something called the Magnus effect. That means that some air sticks to the surface of the ball and spins along with it. Friction slows down this air, meaning that the air on the other side of the ball moves faster.
This leads to the second element at play, known as Bernoulli’s principle. It tells us that a fluid (air in this case) loses some pressure as it gains speed. So the air on the “faster” side of the ball has less pressure than the air on the slow side, pushing the ball toward that weaker side. That’s why curveballs move away from the leading side. All this is true of “normal” balls—or your taped-up Wiffle ball. But all bets are off once those pesky holes come into play. That’s because the air inside the ball has a mind of its own, swirling in circular currents called vortices (the singular is “vortex”). Depending on the speed of the Wiffle ball, these vortices can suddenly strengthen—or temporarily eliminate—the straight movement of the ball.