The direction of the roll is such as to move the bottom of the top back underneath its center of gravity. If you add up these two independent movements, you find that the the vertical movements (turning up, falling down) have cancelled out, so that its net movement is more akin to rolling. I thought the following post would help, but the answers would just bamboozle him I'm afraid. When it comes to old toys, the spinning top is really, really old. What is the purpose of overlapping windows in acoustic signal processing? You might need to draw a picture or use a model to convey this. See also Spinning eggs and ballerinas, Physics Education, 48(1), 51-56 (2013). It precesses at two different frequencies at the same time, about two different vertical axes. Tell everybody about Wonderopolis and its wonders. Dr. Motl's suggestion of a bicycle wheel is a good one. Use this line of reasoning (and the analogy) to explain that 5 clockwise around that axis pointing up, can't magically become 5 clockwise around the axis pointing sideways. Then note that it takes force to stop it from spinning. Ask the child if 5 apples can become 5 oranges magically. Spun slowly clockwise, the egg precesses in a counter-clockwise direction, rocking from one end to the other, in the same way that people move heavy furniture. The first two are a 100 gram aluminium disk with a pointy bottom end, viewed from the side and the top (just before it fell). The basic physics behind all these effects is that a torque is required to rotate an object. Explaining Newton's Laws of motion to a 6 year old. Careful not to catch your nose on the spinning tyre though! How do people live in bunkers & not go crazy with boredom? The spinning top, of course! If the disk was not spinning, it would be impossible to support the disk in that manner. In all three cases, the centre of mass rises when the tops are spun. ? The boy held a metal bar with a wheel on its end (Quite heavy!) But a torque, as something different than force, is tougher. Eventually, though, friction will begin to slow the top's spin. It is smaller than the spin about the vertical axis. Tell the child that the direction and the number they came up with in the previous parts (disregarding mass for the moment, since it is fairly just a scaling factor) can be thought of as an "amount" of spinning, the same way that saying "there are 5 apples" is an amount of objects. On its pointy end, the egg rolls right over then slides. ;-), As we know: we have the difficulty that the motion cannot even be simplified to 2-dimensional motion; gyroscopic precession is irreducibly motion in all three spatial dimensions. +1 I like the last paragraph. All three eggs rise as a result of sliding friction until they start rolling and then the precession frequency is about the same as the spin frequency unlike a sharply pointed top where the precession frequency is much smaller than the spin frequency. If the wheel spins, the gyro generates an upward torque to balance the counter-weight, and the gyro precesses slowly. We sent you SMS, for complete subscription please reply. Did today's Wonder of the Day leave your head spinning? Besides, some adults DO play with spinning tops (check the web), and some make very elegant ones (see www.puccimanuli.com under spinners). Any object that is moving at high speed left to right will continue moving left to right due its momentum, although it can also move up or down if an up or down force is exerted while it is moving. Looking from a child's pov, if you place a top on it's point, it will fall over because it isn't perfectly balanced. At one point near the beginning, the spoon actually slides on the table, but mostly it doesnt because static friction prevents it sliding. Imagine that the red dot is a small bullet attached to the disk. Now imagine the pole is spinning the whole wheel around the vertical axis, similar to a spinning top. A spinning top is not just a childs toy. If it is spinning then it does something else. Pretty sure the child's confusion is that why should, I liked you Russian phrase. The answer you are looking for is "clockwise around an axis of rotation that is pointing up". What determines the direction of precession of a gyroscope? IDEAL OPORTUNIDAD DE INVERSION, CODIGO 4803 OPORTUNIDAD!! When the spoon tilts sideways, it tends to slip sideways on the the table. I'm going to take a stab at this! Lote en Mirador del Lago:3.654 m2.Excelente vista al Lago, LOTE EN EL CONDADO DE 1430 m2, EN COSQUIN. It turns itself completely upside down and ends up spinning with its peg underneath the sphere that was originally spinning underneath the peg used to spin it. It looks like a magic trick with a hidden spider thread holding up the other end. 3 The brass end top takes a while to stand up straight, as shown in the fourth video clip. I'm trying to figure out how to relate things to a 9-year old, and I think things can be conveyed more simply by describing everything in terms of force (which is something he can feel). Explaining conservation of angular momentum is a good idea. If the wheel is not spinning then the counter-balance at the opposite end is not heavy enough to hold the wheel up. Pulling in different directions on the top and bottom of the wheel, makes the whole wheel want to flip over. Stuff falls over because the earth's gravity acts on it with a force to pull it down. rev2022.7.29.42699. The spinning top rotates around an unseen principal axis. The top is spinning around a vertical axis and the spinning around this axis can't disappear. First you need to explain how the speed of points on a spinning object changes with distance from the axis of rotation. OK, I'll give it a shot. EXCELENTE OPORTUNIDAD DEPARTAMENTO CNTRICO EN COSQUIN, OPORTUNIDAD CHALET VILLA MIRADOR DEL LAGO. See Eur J Phys Jan 2018. Hi, Xander! The angular momentum vector L points along the spin axis and rises slowly as the top rises. Here is a spinning hollow plastic egg, a solid wood egg and a solid aluminum egg. There is an even simpler explanation. Junior employee has made really slow progress. Now you can try to explain the gyroscope using these two principles that the kid understands. Point out that it takes force to get it moving and to stop it moving. If an egg is on its fat end when it falls, it slides forward. Your 9-year old son? It's going too slow for the bigger circle, so it creates a 'drag' on the wheel, shown by the second arrow. No formulas required! Conclude by asking them the leading question "If nothing is touching or bothering the top, why would the amount of spinning change?". (b) The egg rotates initially with \Omega much larger than \omega so point P slides out of the page and the sliding friction force on the egg acts into the page. The pressure applied to the top to start the spinning motion is called torque. The red/white sphere has two metal nuts near the middle, screwed onto nylon thread. Now you have shown that spinning something in one direction and then rotating it in a second direction makes it want to flip over in a third direction, at a right angle to the other two. It precesses once in 1400 frames or in 1400/600 = 2.3 seconds so it precesses at 0.43 Hz or 26 rpm. Bangalore? As the top's spin continues to slow, it precesses faster in an attempt to conserve its total angular momentum. If the pencil pivots about the bottom end, static friction prevents the bottom end from sliding. Step 1 I used two small pieces a Blu-Tack, a re-usable adhesive. We believe youll find tomorrows Wonder of the Day to be super cool! Because the spin axis must fall sideways, the torque makes the top fall sideways rather than straight down. I would strongly recommend against reaching to such an analogy to explain a gyroscope to someone. The secret of a rattleback is that the distribution of mass is not lined up with the geometric axis. In the video I started the spoon rocking by pushing down on one end and then releasing the spoon. That is the best way to measure the spin about the long axis. A spinning egg is just as amazing. Most tops are put into motion by twisting the top stem with a snap and releasing. How is Number Of Confirmations derived for a transaction? It is a super cool toy! The scientific forces that make it such a fun toy, however, give us a brief peek into advanced physics. How can I get an AnyDice conditional to convert a sequence to a boolean? The egg rotates initially with \Omega much larger than \omega so point P slides out of the page and the sliding friction force on the egg acts into the page. The green sphere has a small piece of blu-tak in the bottom. But most surprisingly the scientist put up a tick in front of the bar and roundabout stopped immediately. In order to understand the behaviour of a spinning egg, it is necessary to understand the effect of the forces on the egg. Help spread the wonder of families learning together. Of course energy is used every time the top must lift itself, so it eventually slows down and crashes. Suppose that a top is spinning counter-clockwise viewed from above and suppose it is upright, as drawn on the left side of the diagram. The angular momentum vector L points along the spin axis and rises slowly as the top rises. As long as the top keeps spinning, the flipping effect means it can't fall over! We're glad you liked this Wonder! A gyroscope is not actually self-stable: perturb it and it by default preserves the perturbation. It has further to go, so it must go faster in order to get all the way around in the same time. See also e.g. I might not have recorded the details of the experiment accurately but maybe the BBC archives might have a recording or may be some one could replicate the experiment, record it, and post it on YouTube? It's possible that the first spinning top toy was nothing more than an acorn put into motion by a curious kid. The string swings out from the vertical to provide a centripetal force on the gyro since the gyro rotates slowly in a circular path about the vertical axis. Youve matched all of the definitions correctly. But I've noticed that the simple concept that momentum represents an amount of motion is underemphasized in U.S. introductory physics courses. Super cool! No one knows exactly how old it is, but it's definitely been around for thousands upon thousands of years. So the top is pulled in two new directions, and the direction it leans changes again. When this occurs, the top begins to wobble, demonstrating a scientific principle called precession. Dear Peter, be sure that I agree and I know what torque is - but your comments are, in my opinion, not quite appropriate for a nine-year-old, at least not an average one. When you think of your favorite childhood toys, what comes to mind? That is how the two Fs are acting when the disk rotates out of the screen. Whether you spin the top with your fingers or hold the top upright while you pull a string to start it spinning, the top spins rapidly, miraculously staying upright for a long time before eventually beginning to wobble and finally fall back onto its side. I cant remember what the mathematics was behind this but I knew the boy could easily move the heavy bar up and down. In a short amount of time, the rightmost part of the top would have experienced a downward acceleration, but, at the same time, travelled, lets say, a quarter rotation, which would have moved it upwards again and towards us (with no gravity). looking down on the spinning top from above, when it is spinning perfectly balanced. The plastic egg was spun at a low speed and didnt stand upright, but that was done deliberately to record its motion at low speed. Gravity causes the whole top to tip to the right when viewed from the front, but the red dot will tend to move in a straight line since it is moving at high speed. When a spinning top starts to tilt, the point in contact with the supporting surface shifts away from the axis causing the top to roll. This is why the wobbling gets worse right before it falls and comes to a stop. I told him that scientists like to call this inertia. I love wonderopolis, for an unlimited or unspecified period of time, in a manner highly improbable and extraordinary and bringing very welcome consequences, relatively long in duration; tediously protracted, a statement or account that makes something clear, something regarded with special favor or liking, the center around which something rotates, a series with a definite pattern of advance, the outer boundary of an artifact or a material layer constituting or resembling such a boundary, http://www.byron.com/topbook/history.html, http://www.ehow.com/how-does_4964211_spinning-top-work.html, http://www.livescience.com/33614-the-cool-physics-of-7-toys.html. If spun fast enough, a spinning top will rise to a vertical position and happily stay there, despite the fact that it will fall over if it stops spinning. This minimizes the amount of friction generated by its contact with the surface below it. A coin or any other disk rolls on its edge and slowly falls due to slow precession around the Y axis. Imagine the top from, well the top. You might also show him that when he spins on a desk chair, his 'speed' changes when he holds h, +1 for the bicycle wheel suggestion. Give the child a top and ask them to come up with some way to give a number to describe the spinning. But most tops aren't perfect and will begin to lose their momentum. When a spinning top starts to wobble and then falls over, that is because torque starts to pull on the bottom of the top as its spinning slows. This rotates the top in that direction. When it's spinning, you have the linear momentum AND the angular momentum resisting gravity. The spoon therefore has a preferred direction of rotation. The two dots must do the same number of turns per second around the middle, but the outer dot travels in a bigger circle. I would like to add another explanation that is probably at the 9-year-old level. Instead of falling down, it falls sideways. We're glad you're having fun WONDERing! Friction acts in the opposite direction to motion of the bottom end. And that's why it takes longer to fall over. Bicycles will actually correct such perturbations. My nine year old son asked me this very question when playing with his "Battle Strikers" set. The outward force of the marbles away from their central axis of rotation would resist this change, thereby causing a resistance to the twisting action on the axis of the wheel. Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Over time, it was probably a natural progression to begin carving pieces of wood into acorn-shaped toys. Nevertheless, there is a simple explanation, and it involves the effect of friction. For some children, older video game consoles may hold good memories. I have one those toys its like 50 years old. See The Physics Teacher, 51(12), 544-545 (2013) for further details. There is no such torque acting on the disk, so this cant happen unless a horizontal force is applied to the axle in an attempt to reduce the precession frequency. ;-) You must be from a nation South from mine, right? Then I asked him what would happen to the marble if the moving box suddenly stopped. More practically, I would probably take a wheel from a bicycle, made the kid hold it, rotate it quickly, and then make him or her feel the forces when he tries to change the direction of the wheel. Here is a gyroscope from www.gyroscope.com Click the image to see it precess. Disregarding the term moment you can describe angular momentum (and linear momentum) as an amount of motion, since quantities of things is something a 9 year old should be fairly familiar with, I propose pivoting explanations around this interpretation. G rises since the top precesses about the Y axis due to the friction force in the Y direction. The best answers are voted up and rise to the top, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company. If you look carefully you will see that the spoon rocks from side to side and from end to end while it rotates. How do I explain why a spinning top doesn't fall down without going into the mathematics of angular momentum? the Wonder of the Day via email or SMS. The usual explanation is that the change in angular momentum must be in the same direction as the torque on the top that is, in the sideways direction. I told him that scientists like to call these phenomena rotational inertia and the centrifugal force. the direction of the angular momentum vector). Asking the child if they can identify if anything is actually touching the spinning top. When the strip rocks from one end to the other, it falls to the heavy side so the whole strip rotates in that direction. The red dot on the front edge represents a small part of the top, and it is moving left to right at high speed. It turns at a certain speed, a number of turns per second. 2 Proceed to ask the child to assign a direction to the spinning. The key here is to appreciate the independence of the marbles axis of rotation from that of the boxes attached to the wheel. See Eur J Phys Jan 2018. Now imagine a point at the top of the wheel (dm2) and you rotate the wheel to bring it toward the outer edge. Suppose the mass begins to tip to the right. Momentum as an english term is somewhat abstract, imho. Lets be practical and think with the mind of 9 year old, this is my approach: Tell him to stretch his arms and start spinning and now tell him to fold his arms and start spinning again (make sure he doesnt do it vigorously ) and now ask his observation saying which one was easy and say the same feeling would have been to the spinning top if it could think , you can then show his feet (compare with the tops axial) and say you are able to spin without falling as you are maintaining your position and speed relative to this point, Hope this will clear your child's doubt :). As soon as the top starts leaning in a different direction, that becomes the new direction that gravity tries to tip it over in. Its centre of mass rises slowly since the brass ball rolls and the friction force at the bottom end is relatively small. The egg is sliding rather than rolling on the horizontal surface in this case so there is a relatively large friction force on the egg. Vancouver? Then, have him push you around in a circle (or an arc), so he can understand that it takes force to change the direction something is moving in. YouTube videos of the experiment can be found at http://youtu.be/GeyDf4ooPdo and http://youtu.be/tLMpdBjA2SU. :). There are many theoretical papers on the subject and many videos of rattlebacks on YouTube, but there are no simple explanations. Why don't spinning tops fall over? Why does the axis of spinning tops rotate about a vertical axis? LOTE EN VA PARQUE SIQUIMAN A 2 CUADRAS DE LAGO SAN ROQUE. The egg therefore rises. A spinning top is remarkable because it tends to defy gravity while it is spinning. This is a pretty nice yet simple toy in various science museums, including "Techmania" we have here in Pilsen. Imagine (or better, draw!) All are described by Eulers angular momentum equation which relates the change in angular momentum to the torque on the object. Purely mechanical description of how gravity causes a gyroscope to precess, Physics of the point of contact for a spinning top, Torque and angular acceleration with bicycle wheel. The tops were filmed at 300 fps to measure their spin and rate of precession. Brass disk on P800 emery paper at 300 fps. Dont miss our special deals, gifts and promotions. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. To really distinguish torque from force, one needs some vector calculus - and cross product. Also shown are two spherical tippe tops. However, if it is not spun fast enough, sliding eventually gives way to rolling. Viewed from the rear, the top falls to the left. It's not as if you're gonna have the kid understanding all the details (like nutation) without going through the math. I filmed the Herculian effort at 300 fps. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. When the direction that gravity is trying to rotate the top in changes, the direction it tries to flip in also changes, to stay 90-degrees away. We are undergoing some spring clearing site maintenance and need to temporarily disable the commenting feature. Here is another explanation. :), That's GREAT, Joe! This was to encourage him to think about the marbles apparent reluctance to start moving and reluctance to stop moving once it had started. The other end bobs up and down rapidly due to nutation. If you have a dolly with rotatable wheels, sit on it and have him push you around. Then note that it takes force to change the direction of spinning (i.e. The bottom end of the pencil would either slide on the table or pivot about the bottom end, depending on the coefficient of friction. The top rotates with \omega much larger than \Omega and tends to roll on the surface. A pair of forces is OK for a nine-year-old. For further details, see Spherical Tippe Tops in The Physics Teacher, 51(3), 144-145 (2013). 4 In any case, the potential energy within the top is released, changing to kinetic energy, the energy of movement and motion. As a result, the rear edge of the top tilts down. Is it possible to understand the Gyroscope Effect Intuitively? Along time ago (1960's) I saw on TV a show where a scientist was explaining the working of a spinning top in front of an audience of children. In this case, however, I'm stumped. In 1974, Professor Eric Laithwaite showed that he could lift an 18 kg disk above his head, using one hand, when the disk was spinning on the end of a 0.9 m long axle. The tippe top rotates in the opposite direction to the egg (that is, \theta increases) since the sliding friction force is in the opposite direction. We're glad you liked today's Wonder! Now imagine a dot on the outer edge of the spinning top, and another dot halfway toward the center. It's going too fast for the smaller circle, so it creates a 'pull' on the wheel, shown by the arrow. In Feb 2014, Derek Muller repeated the experiment. Designed by, INVERSORES! What are we talking about? Why would you need 3 words to express such a simple idea? Here are three more slow motion video clips showing what happens when an egg falls from rest and when an egg is spun very slowly. Announcing the Stacks Editor Beta release! Are Banksy's 2018 Paris murals still visible in Paris and if so, where? Remember, this is trying to explain to a kid without using complicated maths or formal terminalogy. If a hard-boiled egg is spun fast enough it will rise up and spin on one end. A horizontal force applied to increase the precession frequency would cause the disk to rise. That's a lot of complexity to wrap one's head around. As with a rolling ball on a horizontal surface, there is a small offset in the line of action of N, resulting in a torque that opposes the torque due to the horizontal rolling friction force. The analogy being that you have a number and a qualifier, apples corresponds to a direction, 5 corresponds to the angular velocity. The principle of conservation of angular momentum holds that the top would keep spinning indefinitely if there were no other external forces acting upon it. That is simply amazing. How do you explain spinning tops to a nine year old?
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