Pendulums have an important place in the history of science and technology. They are also excellent devices for exploring science because they illustrate several fundamental concepts in mechanics, and are simple to make and manipulate. What opportunities do they provide in the science classroom?
A playground swing or a tyre suspended from a tree by a rope are familiar examples of a pendulum. In a classroom, pendulums can be used to illustrate several fundamental concepts in middle- and high-school physics, like periodic motion, simple harmonic motion, velocity and acceleration, gravity, the laws of motion, and conservation of energy (see Box 1)
Box 1. Topics in NCERT’s science curriculum that are linked to pendulums:
- Grade VI: Motion and measurement of distances
- Grade VII: Motion and Time
- Grade IX: Motion, Force and laws of motion, Gravitation, Work and energy
A simple pendulum is an idealised pendulum in which we assume that a mass (the pendulum bob) is suspended from a rigid, massless string, and is free to swing back and forth (see Fig. 1).
We also assume that there is no friction or air resistance. When the bob is displaced by a small angle from its equilibrium position, it moves back and forth in a regular and repetitive manner — an example of simple harmonic motion.
The velocity of the pendulum bob changes as it oscillates about its equilibrium position. The velocity is maximum at the lowest point, and is zero when it is at its highest point. Thus, as the bob moves upwards, the kinetic energy decreases and the potential energy increases. The total amount of energy remains constant (see Box 2).
Box 2. You can find more about the physics of pendulums here:
- 1. Henderson, T. The Physics Classroom Tutorial. Retrieved December 26, 2019, from https://www.physicsclassroom.com/class/waves/Lesson‑0/Pendulum-Motion
- 2. University of Colorado Boulder. (2019) Pendulum lab. Retrieved December 26, 2019, from https://phet.colorado.edu/sims/html/pendulum-lab/latest/pendulum-lab_en.html
Pendulums in the classroom
Pendulums are ideal devices for classroom investigations — they are simple, inexpensive, and easy to manipulate.
Initial discussions in the classroom can uncover students’ preconceptions about pendulum motion, and can help them design an investigation to test their beliefs (see Box 3).1
Box 3: Classroom investigations
Students have many ideas about natural phenomena based on their daily experiences and superficial observations. The science classroom can provide students with opportunities to explore these ideas, and modify them based on their own investigations.
These kinds of investigations have multiple benefits. Students gain experience in conducting a practical activity, and in developing their ideas based on evidence and reasoning.
They develop science process skills like systematic observation, careful measurement, and conducting a ‘fair’ test — all of which are an essential part of learning the methods of science. These activities also increase engagement with, and understanding of science.
Process skills enable students to use the methods of science in exploring and understanding concepts.2 They include both mental skills like predicting or evaluating, and physical skills like using tools and materials effectively.
Investigations and accompanying discussions in the science classroom can help students develop process skills at an age-appropriate level.
Some examples of process skills that can be developed in the accompanying pendulum activities include:
- Devising an investigation: identifying what variables are to be kept constant for a fair test, identifying what is to be measured, deciding the order of steps in the investigation.
- Handling and manipulating equipment: using tools and instruments effectively and carefully, assembling the parts as planned.
- Measuring and calculating: measuring variables like time and length accurately, thinking about different errors in measurement and how to minimise them, recording data systematically, calculating average results correctly.
- Finding patterns and relationships: identifying a relationship between variables, checking an inferred relationship against evidence.
For example, students may believe that a heavier pendulum moves slower than a lighter one. Or that a pendulum takes longer to complete an oscillation if its displacement is greater.
The Activity Sheets (I‑VI) accompanying this article can help students investigate these ideas, and discover factors that affect the time period of a pendulum.
Pendulums beyond the classroom
Pendulums have always existed — a child on a swing or a lamp hanging from the ceiling are common examples. But the idealised pendulum that we study in a science class is a more recent concept.
One of the earliest known uses of a pendulum was in a 1st century seismometer device developed by Zhang Heng, a scientist from Han Dynasty, China.3
The first scientific investigation of the motion of a pendulum was conducted by Galileo, in 1602, after he observed the chandeliers in a church swinging periodically. His investigations led to the use of the pendulum as a timekeeping device.
Accurate time measurement was necessary to determine longitudes when navigating on open seas. This was important to European colonisers who were seeking to expand their trade beyond Europe.
Thus, pendulum research in the 18th and 19th centuries focussed on the quest for more accurate timekeeping.4 This, in turn, led to more accurate mapmaking, as well as the expansion of European commerce, colonisation, and exploitation, with far-reachin effects across the world.
The pendulum was also studied by Huygens, Newton, and Hooke — other prominent 17th century scientists (see Fig. 2).
It has also played a significant role in establishing the value of gravitational acceleration ‘g’, its variation with latitude and, hence, in establishing the shape of the earth.5
The many ways in which the pendulum has featured in the history of science and technology, and in the making of the modern world are fascinating.
Cross-curricular projects around these ideas can provide an opportunity for students to understand how science and technology evolve and how they are inextricably linked with the economic, social, and cultural issues of the time (see Box 4).
Box 4. Some cross-curricular project ideas related to pendulums:
• Researching and replicating Galileo’s pendulum experiments.
• Researching the history of timekeeping devices.
• Researching European expansion — navigation, the longitude problem, and timekeeping.
• Where are pendulums used today?
• What is a Foucault’s pendulum?
• Constructing a clock escapement.
- Pendulums can be used to illustrate many fundamental concepts in mechanics like motion, gravity, and energy.
- They are easy for students to make and use for investigations in the science classroom.
- Students can explore the significance of pendulums in the history of science and technology through cross-curricular projects.
- Duckworth, E. R. (2009). ‘The having of wonderful ideas and other essays on teaching and learning’. New York: Teachers College, Columbia University.
- Harlen, W., & Elstgeest, J. (1992). ‘Unesco sourcebook for science in the primary school’. Paris: Unesco Publishing.
- Pendulum. (2019, December 17). Retrieved December 26, 2019, from https://en.wikipedia.org/wiki/Pendulum
- Waring, S. Cambridge Digital Library. Retrieved December 26, 2019, from https://cudl.lib.cam.ac.uk/view/ES-LON-00031/1
- Matthews, M. R. (2000). ‘Time for science education: how teaching the history and philosophy of pendulum motion can contribute to science literacy’. New York: Kluwer Academic/Plenum Publishers.
About the author
Kavita Krishna graduated from IIT Madras and worked as an engineer for 10 years. She retrained as a teacher, and has over 15 years of experience in teaching, curriculum development, and teacher education in rural and urban schools.
She can be reached at email@example.com