Most people enjoy going to playgrounds and playing on the swings. But did you know that the movement of swings—or pendulums— is one of the most studied problems in physics? Understanding their movement has helped people tell time, keep the beat or rhythm in music, and protect buildings against Earthquakes. Do you know what causes a swing to move back and forth if you only raise it and release it? When a pendulum swings there are lots of variables that could go into changing how it swings. In this experiment students will learn what these variables are that affect a pendulum’s swing. In this activity, students will design experiments to identify what these variables are and how they affect the movement of the pendulum.
Science Education: Learning opportunities offered by a pendulum in the science classroom
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 )
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 ).
- 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
- Devisinganinvestigation: 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 1 st 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 18 th and 19 th 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 17 th 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.
Tree Of Life Wooden Clock – Mechanical Pendulum Wall Clock Finished In Walnut
Just a quick note – I’m very proud of my clocks, I love designing and making them and want my customers to feel equally proud of their purchase. It can be difficult to convey the quality of a product online, the feel of the wood, the sound of the ticking and so on. If you would like to see the clocks you are more than welcome to visit me at my home studio where I have several clocks on display. To arrange an appointment please contact me before visiting. Thanks Darren
Introducing my first clock in the Just Nature Collection “The Tree Of Life” finished in walnut with oak leaves.
The tree of life pendulum wall clock is a stunning tribute to the interconnectedness of all things in nature. The delicate branches of the tree stretch outwards, reaching towards the sky in a graceful display of vitality and growth.
The intricate details of the leaves and branches are captured in exquisite detail.
As the pendulum swings back and forth, it evokes the gentle sway of the tree’s branches in a soft, soothing rhythm that lulls the viewer into a state of tranquility. With each tick-tock of the clock, the tree of life pendulum wall clock reminds us of our connection to all living things, and encourages us to embrace the beauty and harmony of the natural world.
Key Features
- Tree Of Life front and rear clock frames
- Branch gear centres
- Oak leaf time indicators at 12,3 and 9 with a squirrel at 6 o’clock
- Oak leaves individually placed on branch tips
- Branch with leaf detail hour, minute and second hands
- Tree Of Life etch detail on pendulum bob
Product Video
Dimensions:
Also See Dimension Drawing
- Height – 1217mm
- Width – 566mm
- Depth – 181mm
Materials:
- Main Material Finish – Black American Walnut
- Gear Material Finish – Black American Walnut
- Marquetry Material – Oak
- Clock Bearings – High Quality Deep Groove Sealed Ball Bearings, Maintenance Free
- Shaft Material – Stainless Steel
- Weight Cord – Wear Resistant Kevlar
Design:
- Drive Power – Gravity Powered By a Weight (batteries not needed)
- Winding – Pull Cord Winding For Speed & Ease
- Run Time – 50 Hours
- Pendulum Period – 2 Seconds
- Escapement Design – Grahams Deadbeat (zero recoil)
Where Is Your Clock Going To Be Installed?
It’s worth considering where your clock is going to be installed, please check my “Where To Install Your Clock” page for full details click here.
What Happens Once My Order is Placed?
All of my clocks are made to order. Once you place an order I will contact you regarding the estimated delivery. I aim to have your clock with you within 8 weeks of order but this can be longer or shorter depending on my current workload.
Other Important Information
Material Variations – Please note that the clock is made using real wood veneers, a naturally occurring material which will vary in tone and grain pattern from piece to piece, therefore, although the same species is used, your clock will not exactly match those displayed in the images and product videos. Its also worth mentioning that the type of lighting can change the tone of the material, some lighting will make the wood appear darker whilst warm lighting as used in the videos can give a considerably different feel.
KEY QUESTION:
What variables affect the period of a pendulum?
Before the activity students should know
- The definitions of both amplitude and period.
- Gravity from the Earth makes things fall.
- The force of gravity is always pulling straight down towards the floor
- Force is mass times acceleration.
AFTER the activity students should know
- What variables affect the period of a pendulum and what variables have no effect.
- How to see a system with many variables and design an experiment that gives results that help explain one aspect of the system.
The Science Behind a Pendulum’s Swing
If you look around, there are pendulums everywhere. For example, the swings on the playgrounds or old clocks. Pendulums can be completely mesmerizing, just think of a hypnotist with a swinging watch. What makes them both so useful and so hypnotic is the extreme regularity of their swing. But what causes that? What does the pendulum’s swing depend on? How can the swing of a pendulum be changed? The simplest pendulum has a string with a mass at the end. In this experiment, you will make your own pendulum with a string and other materials to test what variables affect the pendulum’s swing. To start a pendulum swinging, the first thing to do is pull the mass back a little bit, keeping the string straight. When it is pulled back and held, gravity is pulling directly toward the ground and the string is pulling up toward the pivot point, which is your fingers holding the string in the case of the yo-yo. No matter what happens to the mass of the pendulum throughout the swing, gravity will always be pulling straight toward the ground and the string will keep pulling toward the pivot point.
When you let the mass go, gravity pulls it down and the pendulum starts to swing. As it swings, it speeds up as gravity makes it accelerate. Because the string is holding it up, it swings in an arc. When it is at the bottom of its swing the mass is moving as fast as it can and gravity is pulling straight down and the string is pulling straight up. As it swings through the lowest point it starts to swing up the other way, and gravity is now working to slow it down. When the pendulum gets to the top of its swing, it has been slowed down to a stop and the whole process repeats in the other direction.
So what affects how fast a pendulum swings? Gravity is one variable. A pendulum on the moon or Mars would swing at a different speed than one on Earth because the force of gravity would be different. What about a pendulum is space? But, considering you are not taking your class to the moon any time soon, let’s concentrate on some other variables: What would happen if you changed the mass at the end of the string? In Activity One, we learned that different masses always fall at the same rate. Because of this,, changing the pendulum’s mass will not change how fast it swings.
What happens if you start the pendulum’s swing from a greater height, giving it a greater amplitude? It will still take the same time to get through one swing, it will just be going faster at the bottom of the swing. The pendulum has more time to speed up as it is swinging, so it is going faster, but because it is going faster, it covers the larger distance in the same amount of time as a pendulum with a shorter amplitude.
The variable to change is the length of the string. This is the only variable (that we can easily change) that affects the period of a pendulum. The longer the string, the more time it takes for the pendulum to go through one swing. So if you want to design a swing for the playground to go back and forth faster or slower, then you need to change the length of the chains from the pivot point to the swing’s seat. If you’ve ever used a metronome while practicing music, you will remember that the metrinome’s speed is set by sliding the mass.
Pendulum motion is a neat thing to have your students explore in a freeform way. There are only really three variables they can change – mass, length and starting amplitude – and one variable they can measure, the period. In addition to teaching students about pendulums, this activity has them design their own experiment and learn that it’s only useful to change one variable at a time, that they should do repeated trials, and that there are many different ways to represent results, some more useful than others. If you have limited class time, have different groups of students test different variables.
Safety
Students should be supervised when using yo-yo strings and nuts as they can cause injury if used incorrectly.
Getting Started
In the student’s guide, we have asked the students to design their own experiment to test what variables affect a pendulum’s swing. The idea is to encourage them to be creative, to understand how to design experiments, and to think like scientists and engineers. They are given a set of materials that they can use to do their experiments. This is to prompt them, but they should be allowed to use other materials in their design. As the teacher, you can ask prompting questions to get them to think about the different aspects of the experiments. We have included instructions for how to set up the experiment with the just materials included in the kit.
The goal of the experiment is that students understand that mass is not a factor that affects the pendulum’s period. Using the nuts which are of equal mass, they can test if by adding more mass changes the pendulum’s swing. Students should decide which variables they should control for, such as the number of nuts, the length of the string, the angle at which the nut is released , if there is a strong air current that could affect the swing, and consistency of the repeated experiments.
We ask the students to follow the scientific method to design the experiment.
The scientific method has five basic steps, plus one feedback step:
- Make an observation.
- Ask a question.
- Form a hypothesis, or testable explanation.
- Make a prediction based on the hypothesis.
- Test the prediction.
- Iterate: use the results to make new hypotheses or predictions.
Materials
- 2 yo-yo strings
- 4 hex nuts
- A ruler or measuring tape (optional)
- A timer (optional)
- Sheets of graph paper (optional)
If you are working at home and do not have the exact materials, you can always substitute the nuts from some clay or playdough (see other resources for a recipe of homemade playdough). If you do not have either clay or playdough, then find two objects around the house that you can easily tie a string to. The idea is to build your own pendulum and test whether different masses (but same string length) change the pendulum’s period.
In a classroom set up, the students should work in groups. Give them some time to think about the different variables that they could test. Have a class discussion about the variables the different teams came up with, and as a class decide which ones will be tested. Make sure that each group is testing different variables so that they can share their results – science happens in community!
Before starting the experiment, have the students consider the following questions:
- Apart from a swing, which other examples of pendulums can you think of?
- You just learned the definition of a period, what do you think you can use to measure the period of a pendulum?
- What do you think affects how a pendulum’s swing? What are the variables?
- Of the variables you could think of, which ones you would classify as independent variables (variables you change) and which ones you would classify as dependent variables (variables you measure after changing an independent variable)?
Ask students to list some independent variables., and to list ways to change these variables with the materials they have. As a class. discuss the different possibilities and how to test them, then assign a variable to test per group. After each group has completed their tests, then they can share their results and have a class discussion. Before starting the experiment, ask the students to write their hypothesis and record their experimental designs. As they conduct their experiments, students should record their observations for each test. Here are some suggestions to give students if they need prompting for their experiment design and data analysis:
- Make a table where you have the values for your independent variable in one column and the corresponding values for the dependent variable in the other. For example, if you want to see how the pendulum movement changes when you change the length of the string, then the period (the time that takes the pendulum swing one way and back) should be on the dependent variable column, while the length of the string should be on the next column, as the independent variable. Take several measurements with the same length before you test a new length. Do you notice any patterns?
- Try graphing your data. Remember, the independent variable always goes on the “x” axis and the dependent variable goes on the “y” axis. Do you see any patterns now?
- Can you draw any conclusions about what affects the period of the pendulum?
Next Generation of Science Standards:
4-PS4-1. Develop a model of waves to describe patterns in terms of amplitude and wavelength and that waves can cause objects to move.
MS-PS4-1.Use mathematical representations to describe a simple model for waves that includes how the amplitude of a wave is related to the energy in a wave.
