Weight alone isn’t even scratching the surface ... tension.
Recently, the popular daily YouTube series Good Mythical Morning welcomed Cookie Monster and some very random objects in order to test their knowledge of what floats or not. Hosts Rhett McLaughlin and Link Neal both have engineering degrees from long ago, meaning they had some more keen and nuanced insights as to what would sink or float. But one thing that escaped them both was a bowling ball. Did you know many bowling balls float?
Flotation is, well, a “simple” question of physics (an idea that’s flummoxed scores of physics students for centuries). Bowling balls seem heavy, and they are compared to other sports balls, which may also lead you to assume that they’re quite dense. But it isn’t as simple as that, because any bowling ball that weighs less than 12 pounds can float.
Most Americans use the word “bowling” to refer to the specific sport of ten-pin bowling, which dates back at least 200 years in the United States. The standard range of bowling balls—including both those for children and adults—is between six and 16 pounds, putting 12 pounds almost in the center of the distribution. All of these balls have the same volume, as spheres of the same size that have holes drilled in. And they’re all made of solid materials inside. So how does one ball weigh six pounds while another weighs 16?
The answer is in the materials themselves—less dense materials can fill the same space, but weigh far less. The balls are typically layered with three different materials: a shell, a layer of more neutral filler material, and then a dense core that may be made of tiny moving parts. But it’s even more complicated than that, because what’s inside many bowling balls isn’t even symmetrical.
American Chemical Society’s journal Chemical & Engineering News (C&EN) uncovered some of the secrets of the bowling ball in 2017. It cites an astonishing statistic: “Between 1910 and 1980, only one out of about 3,000 bowlers registered with [U.S. Bowling Congress] could score a perfect game—that’s getting a strike 12 times in a row. By 2007, that figure had increased to one out of about 30.” That’s largely thanks to improvements in bowling ball materials and design.
Elite bowlers put spin on the ball, making an arc down the lane that can strike (literally!) the exact sweet spot between the first and second rows of pins. “[T]he inner core is made of powdered metal oxides such as calcium or iron oxide mixed with a resin and catalyst to harden the mixture,” C&EN explains. “This is the heaviest part of the ball, and its shape—whether symmetric like a sphere or asymmetric like a lightbulb—influences how the ball rotates down the lane.”
In a basic, lightweight bowling ball meant to be used by customers at a bowling alley, the core is probably a sphere and not very large. The filler could be solid resin or some other polymer that ends up being lighter in weight than the same amount of water. In a 16-pound ball, the heavy metal core may be the same size, but surrounded by a denser filler material—and the manufacturer will need to balance that ball differently than one that weighs just 12 or 14 pounds.
With so much engineering inside a bowling ball, it’s a bit easier to understand how an object the same size can weigh six or 16 pounds.
STEM educator Steve Spangler explains the math behind floating (or sinking) bowling balls in one of his online lessons, and how the answer lies in their different densities. To calculate an object’s density, you divide its mass by its volume.
A regulation ten-pin bowling ball typically has a circumference of 27 inches, or 68.58 cm, with a radius (r) of 10.92 cm. That means every bowling ball has a volume of roughly 5,452 cubic centimeters (cm3).
The respective densities of bowling balls of the same size (volume) vary because they weigh different amounts. But the density of water never changes: it’s always 1g/cm3. So a bowling ball with a weight of 11 pounds, or 4,994 grams, has a density of 0.92 g/cm3, which is a little less than the density of water. So it will float.
→ density of 11-pound bowling ball = 4,994 grams / 5,452 cm3 = 0.92 g/cm3
Meanwhile, a bowling ball with a mass of 12 pounds, or 5,448 grams, has a density of 0.99 g/cm3. That gives it almost the same density as water, so the ball won’t exactly float, but it won’t completely sink either.
→ density of 12-pound bowling ball = 5,448 grams / 5,452 cm3 = 0.99 g/cm3
But some regulation bowling balls may have a circumference of just under 27 inches, which would decrease the volume and increase the density, causing a slightly smaller 12-pound ball to sink. For example, the smallest regulation bowling ball allowed has a circumference of 26.704 inches, which would give a 12-pound bowling ball of that size a density of 1.03 g/cm3. So, the density of a bowling ball will increase as it goes up in weight, making 13-pound bowling balls and up definitively denser than water.
So what are some other surprising objects that float? Well, the same idea as the bowling ball might apply to something like a relatively lightweight kettlebell, for example. Watermelons are really big and quite heavy, but they’re all water and then a rind, so they do sometimes float. Pumpkins are heavy, but their insides have a lot of air! Other vegetables and fruits float at some sizes, but sink at larger sizes.
On the flip side, milk, which is almost all water with a little bit of protein and fat, is a tiny bit heavier than water; so a full milk carton will sink, but just barely. And one final interesting case is aluminum foil. Aluminum is a lightweight metal, but it’s still far denser than water. Even so, a sheet of aluminum foil will perch atop a pool of water and stay there. This one is tricky because the issue at play is surface tension rather than “true” buoyancy. (Rose and Jack in Titanic couldn’t survive together on debris made of aluminum foil.) If you take the same foil and crumple it up, it will sink. If you push the sheet of foil below the surface, it will sink.
For those who have bowling balls at home, it’s honestly probably not a bad idea to give them a bath anyway—the finger holes are likely teeming with bacteria from everything you’ve touched at your local bowling alley.
Additional reporting by Jessica Coulon.
Caroline Delbert is a writer, avid reader, and contributing editor at Pop Mech. She's also an enthusiast of just about everything. Her favorite topics include nuclear energy, cosmology, math of everyday things, and the philosophy of it all.
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