FEd Fall 2001 Newsletter - Science is a lot of fun with hands-on activities

Fall 2001



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Science is a lot of fun with hands-on activities

Yoshio Kamishina


A boring science class could be changed into one that is full of fun with hands-on activities. Some examples of such activities are demonstrated. These are integrated with subjects like physics and music. The themes of hands-on activities here are limited to mechanical resonance phenomena and characteristics of rotational motion.


The lecture demonstration used to be - and in many countries still is - central to school science teaching, but it has now been replaced in many schools with the ubiquitous class experiment.

Traditional science museums contain collections of, usually old, scientific and technological objects, often enclosed in glass cases, with concise notes explaining their origins and significance. The visitor is expected to walk around, to look, to absorb the information and to move on. The visitor's role is passive, and there is no opportunity to interact with the exhibits. These museums are worthy of conservation. However, many museums are developing a hands-on science section or are changing into interactive science museums.

In a primary school, where an integrated approach to curriculum has been adopted, the subject of science does not exist in isolation. Subjects in the curriculum are not limited by boundaries; rather it is the interdependency of subjects, which is utilized in the learning process. Even in secondary schools, an integrated approach to curriculum can also effective. In the present paper, some examples of hands-on experiments, which integrate physics and music, and physics and play are described.


2-1. A toy frog swing

In our daily lives, phenomena of resonance are commonly observed. First, a tricky experiment that is a feat of magic using conical pendulums. Three different conical pendulums are hung from the same bar with their symmetry axis on a vertical line ( Fig.1). Each pendulum is of different length, and therefore has a different natural frequency. You can cause any one of the pendulum bobs to swing while the other two remain at rest. The trick is very simple. When you move the bar gently forward and backward at the same frequency as that of the pendulum you want to move, only this bob will swing. The others will not move. This is a simple example of resonance phenomenon. k1.jpg (24098 bytes)

Fig. 1. Three sets of conical pendulums.

Second, a toy frog swing. I have developed a model that represents the movement of a real swing as closely as possible by using a toy rubber frog (Fig.2). The legs are made of rubber and fold so that the frog is in sitting position when the air pressure is low in the body of the frog (Fig.3). When air is pumped into the body through a plastic tube inside the hanging rope, the frog stands up on the seat due to the higher air pressure in the legs (Fig.4).

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Fig. 2. A toy frog swing

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Fig. 3. A sitting frog on the seat

Fig. 4. A standing frog on the seat

In this way, you can propel the frog to swing by working a rubber pump. The swing is driven by air pressure through the fine tube connected to the rubber ball pump. When you press the pump, the toy frog stands up on the seat and the length of rope is effectively shortened. A swing can be thought of as a kind of pendulum, and it has own natural frequency determined by the length of the rope. So, if you gently push the back of the frog, the swing rider, at the same frequency as the natural one of the swing, the amplitude of the swing's movement gets larger and larger. This is also a resonance phenomenon. Remember the movement when you played on a swing. You just repeat standing up and sitting down on the seat. Even if nobody pushed you, you could propel the swing by timely up and down movements. Changing the length of the rope, that is the parameter of the system that determines the natural frequency, energizes the swing. This kind of excitation is called parametric. The characteristic of parametric excitation in a swing is that the frequency of excitation, that of pressing the pump in our case, is twice the natural frequency of the swing. When you press the pump twice in a swing cycle, the frog is most energized. Needless to say, you have to press the pump in phase with the frog? swinging. If you do it out of phase, the amplitude of the swing gets smaller and the swing finally stops.

2-2. Musical instruments

Other good examples of resonance phenomenon are various kinds of musical instruments. All non-electronic musical instruments make use of resonance phenomena to amplify the sound volume.

However, here we will discuss only wind instruments. First, a pipe tuning fork is used to demonstrate sound resonance phenomena. A pipe tuning fork is made of a square metal pipe with one end shaped like a tuning fork (Fig.5). For the purposes of this demonstration, I prepared two pipe tuning forks. The lengths of the tuning fork parts are the same; therefore the pitch of the sound will be the same. However, the lengths of the rest of the pipes are different. When you hit the longer tuning fork with the end of pipe open, the sound is loud, and if you close the end of pipe, the volume decreases. On the other hand, when you hit the shorter pipe tuning fork with the end of pipe open, the sound is small, and when you close the end of the pipe the sound gets loud. These two pipe tuning forks clearly show the difference of the resonance conditions of an open-end pipe and a closed end pipe. A semi-quantitative explanation of the difference is as follows. Let the sound velocity be v, the length of the pipe L, the frequency of the sound in resonance with the pipe f, that is the pitch of the sound. The simple theory ignoring the open end correction of the resonance condition of sound in the pipe tells as follows. The resonance condition is given by the formula f = v / 2L for an open-end pipe, while f = v / 4L for a closed pipe. The length of the shorter pipe is adjusted as the sound is loud when the end of the pipe is closed, while that of the longer one is adjusted as it is loud when open for the same pitch of sound.

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Fig. 5. A pair of pipe tuning forks

Next, the principle of making sound in wind instruments. In a wind instrument, the sound is a vibration of air column in the instrument. Wind instruments are roughly grouped into three families: the oboe family, the trumpet family and the flute family. In oboe type instruments, blowing and vibrating a reed or double reeds make the sound. Clarinets and saxophones belong to this family. A model of a reed instrument can be easily made using a plastic drinking straw and a small piece of overhead projector transparency sheet. You can verify that the pitch of the sound gets higher when you shorten the straw. In the trumpet family, sound is made by the vibrating lips of the player, pushed against the mouthpiece (Fig.6). So, it is rather difficult to make sound. Trombones and French horns belong to this family. In the flute family, sound is made by blowing against the edge of the hole in the side of the pipe. There are many kinds of flutes such as bass flutes, alto flutes, piccolos, fifes, recorders and Pan flutes. A model of a Pan flute can be made using a set of test tubes made of glass or plastic (Fig.7). You can change the pitch of each tube by changing the length of air column in the tube.

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Fig. 6. Mouthpieces (left: trumpet, right: trombone)
In all musical instruments, pitch of sound varies when you change the length of the pipe. The method of changing the length is different depending on the type of instrument. A trombone is straightforward. In flutes, recorders, oboes, and so on, you change the length of the pipe by closing and opening holes in the pipes. The lengths of the vibrating air columns in trumpets and French horns are manipulated valves that add or subtract segments k7.jpg (26168 bytes)
Fig. 7. A model Pan-flute


3-1. A top

A top is one of the most popular toys not only for children but also for adults (Fig.8). Why does a top fall down so easily when it is not spinning, while it is in a very stable state when it spins fast? It is a natural question. However, it is rather difficult to answer for primary school pupils and even secondary school students. To understand the mechanism of the stability of a rotating top, you have to learn about the concepts of Angular Momentum, Torque, Conservation of Angular Momentum, Moment of Inertia, and so on. These concepts are too difficult for children to understand. So, I tried to answer the question without using these difficult concepts and mathematics. Instead, I used many demonstration and hands-on experiments to help the students understand these concepts through experience.

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Fig. 8. A conventional Japanese top

The center of mass

The lower the center of mass of an object, the more stable it is when at rest. However, this is not the case when an object is moving. It is not necessarily stable when its center of mass is in the lowest position. For example, think of a simple pendulum. The bob swings and the center of mass goes up and down periodically, and the average position of the center of mass is higher than when the pendulum is at rest. As another example, I showed a couple of bobs connected by a string through a short tube. Hold the tube vertically and keep the upper bob on the tube, with the other bob hanging by the string connected to the upper bob. When these bobs are at rest, the lower bob stays at the lowest position and this form is the most stable. If you rotate the upper bob in the horizontal plane, the lower bob rises as the upper bob moves faster, and the center of mass of the system is also lifted, which means that motion raises the center of mass of the system.

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Fig. 9a. A gyroscope

Angular momentum and torque

The physical quantity characteristic of rotational motion is angular momentum L, which is defined as L = r x P, where r is the position vector relative to a point in space, P is the linear momentum, and x is the cross product (vector product). If there is no external force exerted on a system, angular momentum is conserved, and therefore, the direction of rotating axis does not change. To understand this law qualitatively, I showed an improved gyroscope. In this improved gyroscope, another axis perpendicular to the rotating axis is attached to the outer frame of a usual gyroscope (Fig.9a, 9b). When you suspend the improved gyroscope from chains or strings at the attached axis, it is held effectively at the center of mass against gravity. As a result, neither gravity nor other external force is acting on it. In this situation, when you spin it rapidly, the direction of the rotational axis never changes even if its frame is moved at random. This is because of conservation of angular momentum. Most students are surprised and impressed by this phenomenon. They should recognize it as a characteristic of rotational motion. Next you set the rotational axis of a rapidly spinning improved gyroscope in the horizontal plane and hang a weight at one end of the axis. The axis still remains in the horizontal plane and rotates around the vertical line. If the procedure is repeated while the gyroscope is at rest, the axis drops as soon as the weight is attached. The force acting on the rotational axis is perpendicular to both the direction of gravity and that of the rotation axis. This kind of force is called a torque, and the motion is called precession from an astronomical term. Students should understand this as another characteristic of rotational motion. That? why a rapidly spinning top hardly falls down as the rotational axis rotates around the vertical axis, that is a precession.

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Fig. 9b. An improved gyroscope

3-2. A tippy top

Among a variety of tops, a tippy top is most popular. At a glance, a tippy top is hardly distinguishable from normal tops (Fig.10a, 10b).  A top usually rotates steadily around the rotational axis and the rotational axis rotates around the vertical axis as everyone knows. However a tippy top turns upside down while rotating (Fig.11). The big difference between them is that the usual top falls down when at rest while a tippy top doesn't. It is stable at rest. This means that the center of mass of a conventional top is situated higher and it is therefore unstable at rest, while on a tippy top the center of motion is at the lowest position at rest. Roughly speaking, rotational motion progressively lifts the center of mass of a tippy top, and finally turns it over. The mechanism by which the axis of rotation gradually moves up or down in addition to a precession, moving in a circular cone about the vertical axis, is in large part connected with the action of friction at the point of contact with the floor.

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Fig. 10a. A normal top (spinning)

The quantitative explanation of this mechanism is too difficult for students to understand. The qualitative explanation is more suitable for children. To reproduce the motion of a tippy top, I showed a 2-dimensional tippy top consisting of a large ring and a small ring both made of metal wire (Fig.12). The two rings are attached at a point with the small ring inside the large one on the same plane. The role of the smaller ring is to shift the center of mass of the system away from the center of the large ring. When you rotate the large ring around the vertical axis connecting two centers of both rings with the small ring at the bottom, the system acts like a tippy top. While when you do the same thing but with the small ring at the top it acts like a conventional top. The difference in behavior is the position of the center of mass of the system.

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Fig. 10b. A tippy top (at rest)

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Fig. 11. A tippy top (spinning)

Fig. 12. Two-dimensional tippy top


Physics toys are very good teaching tools. If you make practical use of them and give children proper explanations about the reasons for the behavior of the toys, most children will have fun with physics. It is very important for children to handle the toys themselves. They learn to understand physical concepts not only by reading books and listening to lectures but also from their experiences in daily life. For elementary school pupils, the latter learning method is much more prevalent, and they very often have misconceptions. However, it is worthwhile to mention that preconception is not misconception. Teachers should lead them to scientific conception from non-scientific preconception. As a useful teaching strategy, teachers should offer children proper toys as teaching materials, and let them have first hand experience. Most importantly, children must feel that science is a lot of fun.

Hands-on experiments are really instructive in science education especially for elementary and secondary school pupils.

Yoshio Kamishina is at the Department of Physics, Faculty of Education, Shimane University 1060 Nishikawatsu-cho, Matsue city, Shimane 690-8504 Japan