pendulum ball experiment

The Bowling Ball Pendulum

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Quick Physics : Conservation of Energy tells us that the bowling ball will not go higher than its starting height (without some external force pushing on it).

The Details: A swinging bowling ball illustrates a very important principle of physics: The Conservation of Energy. The total amount of energy an object has stays the same, unless you do something to change it. To change the energy of something, you have to move it (for example, give it a push). The bowling ball starts with a certain amount of potential (stored) energy. It gets this energy because someone had to lift it up to hang it. The bowling ball is heavy and you have to do work to get it up in the air. Whenever we do work on something, we are giving it energy. When you let go of the ball, it swings downward like a pendulum. As it starts swinging, the energy changes from potential energy to kinetic, or moving, energy. The total amount of energy, moving plus stored, stays the same; it only changes form. When the ball swings back to where it started, the energy changes back to potential energy. Since the total energy has to stay constant, the kinetic energy of the ball must be zero and the ball must stop moving. It can’t hit you!

An important qualifier: if you push the ball instead of just letting go, you give the ball some extra kinetic energy. This extra energy makes it swing back farther than when it started. When it comes back, you better duck!

UCSC Physics Demonstration Room

Demonstration Resources for UCSC

Bowling Ball Pendulum

This is an exciting and popular demonstration and shows conservation and transformation of energy for a pendulum. Two setups are available.

Setup:  A modified bowling ball with a hook mount is attached to a cable from the ceiling (Thimann 3 is the only classroom to have the cable).

Procedure:  The instructor leans against the wall while holding the bowling ball close to his/her face. The supporting cable, attached to the ceiling, has to be tight. Then, he/she carefully releases the ball and stays without fear as the bowling ball makes the full swing, returns back, and stops millimeters from his/her face. Brave students can try this too!

All other locations

Setup: A modified bowling ball with a hook mount is attached to a cable hanging from a board clamped between two ladders.

• Two 8-ft tall ladders (one can be borrowed from the campus woodshop)
• Bowling ball with hook mount
• Board with eye hook and cable attached
• Two large clamps to secure the board to the ladders
• Two volunteers to stand on the ladders for extra stability during the demo

Procedure:  The instructor stands behind the ladders while holding the bowling ball close to his/her face. The supporting cable, attached to the board, has to be tight. Then, he/she carefully releases the ball and stays without fear as the bowling ball makes the full swing, returns back, and stops millimeters from his/her face. Brave students can try this too!

Explanation

The other force that acts on the pendulum is the tension force pulling up on the bowling ball. This is not an internal or conservative force so it can change the total mechanical energy of the bowling ball. However, because the force of tension always acts perpendicular to the direction of motion, and

At its highest points, the pendulum will be momentarily motionless. This is because at these points, all of the kinetic energy has been transformed into gravitational potential energy. Conversely, when the pendulum is at the bottom of the arc, its potential energy is zero and it has the highest velocity of any point. Even though the mechanical energy of the system is transformed throughout the period of the pendulum, the total mechanical energy stays constant throughout the cycle, which means that as it is released, the potential energy that it loses is changed over entirely to kinetic energy.

This demonstration also shows conservation of energy. If this were a perfect system where no energy was lost to friction, the amplitude of the pendulum would stay constant for as long as it was swinging. While this pendulum is almost a perfect system, there is still some energy that is lost to air resistance opposing the direction of motion of the bowling ball and friction of the knot attaching the pendulum to the board. This means that we have a damped system and eventually the pendulum will come to rest.  Because there is some energy lost in the system, it is a fun demo to release the bowling ball very close to your face or stomach and watch it come back to within millimeters of where it was released (as long as you don’t move!).

Both air resistance and the friction in the knot are friction forces, which serve to translate kinetic energy into heat. However, even though there is energy being turned into heat on the surface of the bowling ball and in the rope, it is unlikely that you would be able to feel the difference in temperatures because the change will be so small.

• Please request this demo at least three days in advance so we can obtain the ladder from the woodshop.
• This demo requires 2-3 people to set up
• No one should ever stand more than one rung above the ground on the ladders

Written by: Sophia Sholtz

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A mesmerizing pendulum wave demonstration with 16 bowling balls in a north carolina forest, september 9, 2014, christopher jobson.

If you’ve ever been to a science museum or taken a physics class, you’ve probably encountered an example of a pendulum wave . This video shows a large-scale pendulum wave contraption built on private property in the mountains of North Carolina, near Burnsville. The mechanism relies on 16 precisely hung bowling balls on a wooden frame that swing in hypnotic patterns for a cycle of about 2 minute and 40 seconds. Via Maria Ikenberry who filmed the clip:

The length of time it takes a ball to swing back and forth one time to return to its starting position is dependent on the length of the pendulum, not the mass of the ball. A longer pendulum will take longer to complete one cycle than a shorter pendulum. The lengths of the pendula in this demonstration are all different and were calculated so that in about 2:40, the balls all return to the same position at the same time – in that 2:40, the longest pendulum (in front) will oscillate (or go back and forth) 50 times, the next will oscillate 51 times, and on to the last of the 16 pendula which will oscillate 65 times.

Because the piece is outdoors, a number of factors prevent the balls from precisely lining up at the end, but it’s still easy to get the idea. In a perfectly controlled environment you get something like this .

Update: The pendulum was built by Appalachian State University teacher and artist Jeff Goodman .

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This bowling ball experiment demonstrates the beauty of physics

This video is mesmerizing. .

Marissa Fessenden

Internet Culture

Posted on Sep 12, 2014     Updated on May 30, 2021, 2:45 pm CDT

Sixteen bowling balls strung from a wooden frame swing back and forth in unison, then in an undulating curve, then into seeming chaos before lining up once again.

This hypnotic video, peppered with awestruck cries from the onlookers, demonstrates the beauty of math and physics.

Each bowling ball takes a slightly different period of time to swing back and forth. This period depends on the length of the pendulum, not the mass of the ball. Longer pendulums take longer to swing than shorter ones do. The cool way these pendulums synch up has to do with the precise calculations that went into constructing the demonstration. The  video description  on YouTube.com explains:

The lengths of the pendula in this demonstration are all different and were calculated so that in about  2:40 , the balls all return to the same position at the same time – in that  2:40 , the longest pendulum (in front) will oscillate (or go back and forth) 50 times, the next will oscillate 51 times, and on to the last of the 16 pendula which will oscillate 65 times. Try counting how many times the ball in front swings back and forth in the time it takes the balls to line up again, and then count how many times the ball in back swings back and forth in the same time (though it’s much harder to keep your eye on the ball in back!).

Pendulums are  a basic concept in physics  and the wave demonstration is  a common way  to illustrate some of their properties. Since there is a clear relationship between the length and the oscillation period, you can calculate the pendulum lengths by counting those back and forths. Also, you can even  build one yourself .

“I was impressed by the idea that the patterns we see are equally in the math and in our minds,” writes the demonstration’s creator Jeff Goldblum  on his blog . He teaches at Appalachian State University in Boone, N.C. “They are real patterns, but they come about from the relationship of separate objects.” His post also features more videos (including  one in slow motion ) and explains why the bowling balls don’t line up perfectly.

“It wasn’t so easy, and it never was perfect,” he writes. The weight of the ball did change how far out the ball swung over time, the weight of the cable and hooks altered the center of mass for lighter balls, and the beam flexed a bit. “However, it got good enough for us to feel satisfied, and we learned some of the limitations of our materials,” he adds.

Certainly the end result is hypnotic.

Screenshot via  Maria Ikenberry /YouTube.com

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Marissa Fessenden is a science writer whose work has appeared in Scientific American, Smithsonian Magazine, and the Santa Cruz Sentinel. She earned her bachelor of science degree from Cornell University and a certificate in science communication from the University of California, Santa Cruz.

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What's Up With That: How a Swinging Pendulum Proves the Earth Rotates

Once upon a time, you were probably on an elementary school field trip at a science museum or an observatory. Just before lunch, your teacher had the class stand in a circle around an enormous weight suspended on a string, and watch it swing back and forth, back and forth.

The teacher (or maybe a tour guide) explained that if you watched the pendulum for long enough, it would seem to alter its course, swinging in a slightly different direction. And that this somehow proved the Earth was rotating beneath your feet. You probably nodded and watched the weight swing for a while. And even though you didn’t see anything really change, you thought, “Sure,” and then went to trade your friend an Oreo cookie for half of their Hi-C Ecto Cooler.

Now that you’re older, you’ll occasionally think back on that pendulum and wonder how it could have proved anything. After all, the demonstration was in a building on the Earth, so if the Earth was rotating, shouldn’t the pendulum be rotating with it?

This famous experiment, now found in museums around the world , was first demonstrated in 1851. French physicist Leon Foucault suspended a 61-pound weight from a 200-foot-long wire at the Pantheon in Paris and set it swinging. He needed the bob to be so heavy and the wire so long to ensure that the pendulum would be able to swing for a long time, at least an hour. A pin on the bottom of the weight drew a line in a circle of wet sand set underneath the experiment.

After an hour, the line the pin drew in the sand intersected with the first line at an angle of roughly 11.25 degrees, which is exactly what Foucault had predicted. The demonstration was an international sensation and was quickly repeated to crowds across Europe and North America. By this point, everyone knew that the Earth rotated but this was the first experiment to measure the speed at which it did so. Foucault got eternal fame by having a pendulum named after him, which later became the title of a mind-bending book by Umberto Eco you probably tried to read in college before turning to the much easier candy of Dan Brown novels.

So how does this all work? To explain, we’re going to have to do a little thought experiment.

Let’s say that one day you and a friend decide to play a game of catch at the North Pole (your friend is an eccentric billionaire in this story). You stand on one side of the pole and toss the ball directly over the pole to your friend, who is standing opposite you. Try to think about things from the ball’s perspective. At the moment it’s released from your hand, its path is set. It will travel in a straight line toward the point that you threw it. But in the time it takes the ball to travel, the Earth has rotated just a tiny bit. Your friend has moved ever so slightly to the right. This movement is so minute that it’s hardly going to affect your game of catch. But if you were on a planet with a very fast rotation rate, your friend would have moved much more in the time it takes the ball to travel. The ball could entirely miss your friend, going straight past her left arm.

As it goes through its swing, the pendulum acts like this ball. Once the pendulum reaches the top of its arc, its path is set. It will head to the opposite end of its swing without deviation. Essentially, it will continue swinging back and forth in the same exact plane. Imagine you’ve suspended the pendulum over the North Pole. You glue a pin to its bottom and send it swinging, drawing a line in the snow. But in the time it takes to go from one top of an arc to the next, the Earth underneath the experiment has rotated. And each time the pendulum swings; the Earth rotates a little more. If you kept the pendulum swinging for six hours, one-quarter of a day, the line it now traced in the snow would intersect the first line at 90 degrees. (Note: Some truly awesome and dedicated physicists did this in 2001 at the South Pole.)

Those of you checking my math will probably now interject something like this: “But you said that Foucault’s pendulum in Paris moved 11.25 degrees in one hour, which means it would have only changed by 67.5 degrees in six hours, not 90 degrees.” Well congratulations, you’ve shown that the thought experiment we did above only works at either the North or South Pole. And also, that you are a nerd.

Imagine the same setup at the equator. You start the pendulum swinging in a perfect east-west direction. The Earth still rotates each time the weight goes through an arc, but now it’s moving in exactly the same direction as the pendulum. There’s no relative motion. Think about this carefully. I can set the pendulum swinging north-south and the Earth’s rotation still won’t affect the plane it moves in. That’s because the Earth can’t twist underneath the setup; it's always headed in the same direction .

What about points in between the poles and the equator? Well, it requires a little bit of complicated geometry to fully determine exactly how much the Earth moves under the pendulum. Suffice to say that in one day the plane that the pendulum swings in will appear to change somewhere between zero degrees (like at the equator) and 360 degrees (like at the poles). You can derive an equation to tell you exactly how much the Earth moves based on your latitude: n = 360° sin(θ), where θ is your latitude. If your pendulum was drawing lines in sand, like Foucault's, n would be the intersection angle between the first line and a line drawn 24 hours later (actually, it's 23 hours, 56 minutes and 4.1 seconds later – this is a sidereal day , the time it takes for the Earth to rotate once relative to the stars, rather than a 24-hour solar day).

This means that if you ever find yourself trapped in a room with no way out and happen to have a piece of string and weight handy, you can determine your latitude. Isn’t science useful?

Homepage image: Ben Ostrowsky /Wikimedia Commons

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