Skipping stone physics could aid net-tangled whales and more
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Physics
Newfound trajectory for spheres in water could improve things from fishing nets to ships
Many children who grow up near bodies of water attempt to fling stones across the water, making them skip as many times as possible before finally sinking. Similar physics inspired the development of new buoys to help save trapped whales.
Colin Anderson Productions pty ltd/Photodisc/Getty Images Plus
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By Allison Gasparini
October 18, 2023 at 6:30 am
Many fishers cast enormous nets into the ocean to catch lots of fish at once. But such mega-nets can nab other species, too — even big ones, such as whales. For instance, in 2017 off U.S. coasts alone, fishing nets trapped nearly 100 whales . Now, physics similar to that of skipping stones could help better save such trapped mammals.
Large fishing nets have been equipped with floating buoys that sense when the net has trapped a whale. But those buoys experience a lot of drag, or water resistance, as a whale pulls them through the ocean. This makes the whale buoys skip across the sea — somewhat like a smooth stone tossed across the surface of a pond. That movement can boost the stress of a trapped whale. It also can plunge buoys into the water, where they stop sending out signals that help rescuers locate the whale.
In a new study, researchers took a closer look at that skipping stone–like behavior in buoys. This allowed them to better understand how drag affects objects in the water. What they learned helped them design a whale buoy with less bobbing. Their insights might one day be useful in ship design and fishing, too.
The group reported its findings July 11 in Physics of Fluids .
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Understanding drag
Tadd Truscott is a mechanical engineer at King Abdullah University of Science and Technology. That’s in Thuwal, Saudi Arabia. To investigate whale buoys’ movement, his team watched as small, floating buoy-like spheres scuttled along the water’s surface.
For their experiments, the researchers connected a hollow, aluminum sphere to a string. Then they threw it into a long tank filled with water. With the help of a pulley drawing on the string, they dragged the sphere across the tank. Cameras captured its motion in detail.
Truscott expected a pulled sphere to rise out of the water. Instead, pulling a sphere made it dip below the surface. “I was completely shocked,” Truscott says. Even when pulled along from a high angle, a sphere dipped fully underwater .
Like stones skipping on the surface of water, hollow spheres can skip underneath the water. As a buoyant sphere moves underwater (dark sphere at right), a long bubble forms around its surface, which helps stabilize its motion.
Farrukh Kamoliddinov
Another surprise was that a bubble of air formed around the sphere as it moved under the water. And that bubble greatly affected how and where the sphere moved.
Bubbles can create drag, which can make it harder for an object to move through water. “But this study and other studies we’ve done show that sometimes that’s not true,” Truscott says. In this case, the bubble stabilized the sphere.
The bubble around a moving sphere develops a streamlined, wing-shape. This shape, Truscott says, allows the sphere to experience far less drag than if it did not have the cushioning bubble of air.
The air bubble “suppresses the underwater ‘bouncing’ behavior,” explains mechanical engineer Jesse Belden. Although not a part of this project, he too has studied the skipping behavior of spheres on water . Belden works at the Naval Undersea Warfare Center in Newport, R.I.
Applying the findings
Truscott’s team has now designed a better whale buoy based on what the group learned about how these devices move through water. Since their study showed that a spherical buoy will dive under the water, they worked to create a shape that would keep an antenna from submerging.
The new buoy is “shaped much more like a ship,” Truscott says. That design change means it won’t dive under the water’s surface like spheres do. “The redesign also pierces waves much better,” he adds. Both of those features help buoys stay above water, where they can send out signals to whale-rescue teams.
“If we’re going to keep trying to save whales and other species in the ocean from fishing nets — but not stop fishing — then we’re going to [need] devices like the [new one] we designed for the whales,” Truscott says.
Fishing boats often deploy large nets, like the one shown here. They’re meant to catch fish. But sometimes they trap whales, which may die while fighting to break free. A new buoy system might help limit accidental whale netting.
Damocean/iStock/Getty Images Plus
Findings by his team could also be useful for people who design ships, Belden says. Ships tend to burn lots of fuel as they plow through the water, and the more drag they face, the more fuel they use. Cutting drag would lower fuel costs — and ships’ impact on climate change by reducing how much fuel they burn.
Truscott’s team hopes to study how the effects seen here might even apply to other things that move through the water, such as anchors and fishing lures.
“There are all kinds of really interesting fishing devices out there that are probably not very efficient and certainly not designed to move out of the way when a large object like a whale passes through them,” Truscott says. “That’s something that not a lot of people are spending their time on. But certainly,” he says, “we will go down those roads.”
Power Words
More About Power Words
aluminum : A metallic element, the third most abundant in Earth’s crust. It is light and soft, and used in many items from bicycles to spacecraft.
angle : The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.
angler : A term for someone who fishes for food, usually for personal consumption, not on an industrial scale.
application : A particular use or function of something.
behavior : The way something, often a person or other organism, acts towards others, or conducts itself.
buoy : A floating device anchored to the bottom of a body of water. A buoy may mark channels, warn of dangers or carry instruments to measure the environment.
climate change : Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.
drag : A slowing force exerted by air or other fluid surrounding a moving object. It involves friction. But unlike simple friction, it increases with an object’s speed.
dynamic : An adjective that signifies something is active, changing or moving. (noun) The change or range of variability seen or measured within something.
force : Some outside influence that can change the motion of an object, hold objects close to one another, or produce motion or stress in a stationary object.
mechanical engineer : Someone trained in a research field that uses physics to study motion and the properties of materials to design, build and/or test devices.
physics : The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. A scientist who works in such areas is known as a physicist.
stress : (in biology) A factor — such as unusual temperatures, movements, moisture or pollution — that affects the health of a species or ecosystem. (in psychology) A mental, physical, emotional or behavioral reaction to an event or circumstance (stressor) that disturbs a person or animal’s usual state of being or places increased demands on a person or animal; psychological stress can be either positive or negative.
technology : The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.
whale : A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises.
Citations
Journal: F. Kamoliddinov et al. Skipping under water: Buoyant sphere hydrodynamics at the air-water interface . Physics of Fluids. Vol. 35, July 11, 2023. doi: 10.1063/5.0153610.
Report : NOAA Fisheries. National Report on Large Whale Entanglements: Confirmed in the United States in 2017 . November 6, 2018 (updated November 7, 2022). 8 pp.
Meeting: J. Belden. Imaging for new science and new science for imaging . Talk given at a seminar for the Center for Fluid Mechanics in the Division of Applied Mathematics, Fluids, Thermal and Chemical Processes. October 9, 2012, Brown University, Providence, R.I.
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Physics. Newfound trajectory for spheres in water could improve things from fishing nets to ships. Many children who grow up near bodies of water attempt to fling stones across the water, making them skip as many times as possible before finally sinking. Similar physics inspired the development of new buoys to help save trapped whales. Colin Anderson Productions pty ltd/Photodisc/Getty Images Plus. Share this: Email. Facebook. Twitter. Pinterest. Reddit. Google Classroom. Print. By Allison Gasparini. October 18, 2023 at 6:30 am. Many fishers cast enormous nets into the ocean to catch lots of fish at once. But such mega-nets can nab other species, too — even big ones, such as whales. For instance, in 2017 off U.S. coasts alone, fishing nets trapped nearly 100 whales . Now, physics similar to that of skipping stones could help better save such trapped mammals. Large fishing nets have been equipped with floating buoys that sense when the net has trapped a whale. But those buoys experience a lot of drag, or water resistance, as a whale pulls them through the ocean. This makes the whale buoys skip across the sea — somewhat like a smooth stone tossed across the surface of a pond. That movement can boost the stress of a trapped whale. It also can plunge buoys into the water, where they stop sending out signals that help rescuers locate the whale. In a new study, researchers took a closer look at that skipping stone–like behavior in buoys. This allowed them to better understand how drag affects objects in the water. What they learned helped them design a whale buoy with less bobbing. Their insights might one day be useful in ship design and fishing, too. The group reported its findings July 11 in Physics of Fluids . Educators and Parents, Sign Up for The Cheat Sheet. Weekly updates to help you use Science News Explores in the learning environment. Thank you for signing up! There was a problem signing you up. Understanding drag. Tadd Truscott is a mechanical engineer at King Abdullah University of Science and Technology. That’s in Thuwal, Saudi Arabia. To investigate whale buoys’ movement, his team watched as small, floating buoy-like spheres scuttled along the water’s surface. For their experiments, the researchers connected a hollow, aluminum sphere to a string. Then they threw it into a long tank filled with water. With the help of a pulley drawing on the string, they dragged the sphere across the tank. Cameras captured its motion in detail. Truscott expected a pulled sphere to rise out of the water. Instead, pulling a sphere made it dip below the surface. “I was completely shocked,” Truscott says. Even when pulled along from a high angle, a sphere dipped fully underwater . Like stones skipping on the surface of water, hollow spheres can skip underneath the water. As a buoyant sphere moves underwater (dark sphere at right), a long bubble forms around its surface, which helps stabilize its motion. Farrukh Kamoliddinov. Another surprise was that a bubble of air formed around the sphere as it moved under the water. And that bubble greatly affected how and where the sphere moved. Bubbles can create drag, which can make it harder for an object to move through water. “But this study and other studies we’ve done show that sometimes that’s not true,” Truscott says. In this case, the bubble stabilized the sphere. The bubble around a moving sphere develops a streamlined, wing-shape. This shape, Truscott says, allows the sphere to experience far less drag than if it did not have the cushioning bubble of air. The air bubble “suppresses the underwater ‘bouncing’ behavior,” explains mechanical engineer Jesse Belden. Although not a part of this project, he too has studied the skipping behavior of spheres on water . Belden works at the Naval Undersea Warfare Center in Newport, R.I. Applying the findings. Truscott’s team has now designed a better whale buoy based on what the group learned about how these devices move through water. Since their study showed that a spherical buoy will dive under the water, they worked to create a shape that would keep an antenna from submerging. The new buoy is “shaped much more like a ship,” Truscott says. That design change means it won’t dive under the water’s surface like spheres do. “The redesign also pierces waves much better,” he adds. Both of those features help buoys stay above water, where they can send out signals to whale-rescue teams. “If we’re going to keep trying to save whales and other species in the ocean from fishing nets — but not stop fishing — then we’re going to [need] devices like the [new one] we designed for the whales,” Truscott says. Fishing boats often deploy large nets, like the one shown here. They’re meant to catch fish. But sometimes they trap whales, which may die while fighting to break free. A new buoy system might help limit accidental whale netting. Damocean/iStock/Getty Images Plus. Findings by his team could also be useful for people who design ships, Belden says. Ships tend to burn lots of fuel as they plow through the water, and the more drag they face, the more fuel they use. Cutting drag would lower fuel costs — and ships’ impact on climate change by reducing how much fuel they burn. Truscott’s team hopes to study how the effects seen here might even apply to other things that move through the water, such as anchors and fishing lures. “There are all kinds of really interesting fishing devices out there that are probably not very efficient and certainly not designed to move out of the way when a large object like a whale passes through them,” Truscott says. “That’s something that not a lot of people are spending their time on. But certainly,” he says, “we will go down those roads.” Power Words. More About Power Words. aluminum : A metallic element, the third most abundant in Earth’s crust. It is light and soft, and used in many items from bicycles to spacecraft. angle : The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet. angler : A term for someone who fishes for food, usually for personal consumption, not on an industrial scale. application : A particular use or function of something. behavior : The way something, often a person or other organism, acts towards others, or conducts itself. buoy : A floating device anchored to the bottom of a body of water. A buoy may mark channels, warn of dangers or carry instruments to measure the environment. climate change : Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests. drag : A slowing force exerted by air or other fluid surrounding a moving object. It involves friction. But unlike simple friction, it increases with an object’s speed. dynamic : An adjective that signifies something is active, changing or moving. (noun) The change or range of variability seen or measured within something. force : Some outside influence that can change the motion of an object, hold objects close to one another, or produce motion or stress in a stationary object. mechanical engineer : Someone trained in a research field that uses physics to study motion and the properties of materials to design, build and/or test devices. physics : The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. A scientist who works in such areas is known as a physicist. stress : (in biology) A factor — such as unusual temperatures, movements, moisture or pollution — that affects the health of a species or ecosystem. (in psychology) A mental, physical, emotional or behavioral reaction to an event or circumstance (stressor) that disturbs a person or animal’s usual state of being or places increased demands on a person or animal; psychological stress can be either positive or negative. technology : The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts. whale : A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises. Citations. Journal: F. Kamoliddinov et al. Skipping under water: Buoyant sphere hydrodynamics at the air-water interface . Physics of Fluids. Vol. 35, July 11, 2023. doi: 10.1063/5.0153610. Report : NOAA Fisheries. National Report on Large Whale Entanglements: Confirmed in the United States in 2017 . November 6, 2018 (updated November 7, 2022). 8 pp. Meeting: J. Belden. Imaging for new science and new science for imaging . Talk given at a seminar for the Center for Fluid Mechanics in the Division of Applied Mathematics, Fluids, Thermal and Chemical Processes. October 9, 2012, Brown University, Providence, R.I. Classroom Resources for This Article. Free educator resources are available for this article. Register to access: Already Registered? Enter your e-mail address above. Classroom Questions. Power Words. Readability Score: 6.8. Related Stories. Animals What a drag! Fishing gear’s effects on whales By Ilima Loomis January 13, 2016. Animals Let’s learn about whales and dolphins By Sarah Zielinski June 22, 2021. Animals Whale of a lesson By Eric Wagner March 7, 2013.