SummaryStudent teams creatively construct mobiles using hangers and assorted materials and objects while exploring the principles of balance and center of mass. They build complex, free-hanging structures by balancing pieces with different lengths, weights, shapes and sizes.
Exploring the principles of balance and center of mass can be an interesting endeavor. Finding the center of mass is a key factor in many engineering designs. For example, engineers design cars, bicycles, washing machines, CD players and all kinds of vehicles, as well as tools and other devices to make sure that while in motion the objects behave as intended. Achieving balance and equilibrium also applies to the design of structures such as bridges and skyscrapers.
An understanding of the concept of center of mass.
After this activity, students should be able to apply their understanding of center of mass and balance to build complex, free-hanging structures by balancing pieces with different weights at different points on hangers.
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Each TeachEngineering lesson or activity is correlated to one or more K-12 science,
technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN),
a project of D2L (www.achievementstandards.org).
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within type by subtype, then by grade, etc.
Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.
- various pieces of materials and objects with hooks on them
Think of all the times you use your body to try to balance. Maybe on one foot? Maybe upsidedown on your two hands? On a skateboard, bicycle or log across a stream? Or maybe while carrying many items with your arms full? Our sense of balance keeps us from falling and enables us to move skillfully.
For engineers who design design structures, such as bridges and skyscrapers, and products, such as wheels, washing machines and the spinning drives in computers and music players, balance is an important concept. If these items are not in balance, they are unstable and fall over or don't work!
Every object on our planet has what we call a center of mass. The center of mass is the point that you must find to determine if an object is in balance or not. Have you noticed that when you try to walk on a curb you automatically pull your arms in and out, making little adjustments around your body's center of mass so that you stay balanced? Yes? Then you know what I'm talking about!
Today we're going to explore the concept of center of mass by making mobiles.Working in groups, your challenge is to create a complex arrangement of many different objects, combining them into one balanced mobile. Remember that every object has a center of mass that it can balance on. Using this knowledge, you are ready to build complex, free-hanging structures by balancing pieces with different weights, shapes and sizes. Let's get started!
Before the Activity
- Ask students to bring in small objects of different shapes and materials to class.
- Gather materials.
- Prepare enough example display units so that each group gets one. A display unit consists of a hook attached to the top of the display/hanger and various objects with hooks with which children can create their own mobiles. Each piece can have two or more pieces hanging off either end. In this way, the original piece hanging from the hook can hold many more balanced pieces below it.
With the Students
- Divide the class into teams of three students each.
- Hand out a display unit to each group along with at least two extra hangers.
- Ask students to place the objects on the hangers at different points and then add them on to the main unit such that the entire stucture is balanced.
- Discuss the center of mass concept as students experiment to find balance using the various objects.
- Discuss real-life engineerig examples in which the center of mass is important to the correct functioning of products and tools.
Project Evaluation: Grade team mobiles using a rubric with criteria such as the number of objects used, the number of different shapes and sizes of materials used and design complexity.
ContributorsAdebayo Adeyinka; Lee Fisher; Mark Liffiton
Copyright© 2013 by Regents of the University of Colorado; original © 2005 Worcester Polytechnic Institute
Supporting ProgramCenter for Engineering Educational Outreach, Tufts University
Last modified: August 23, 2017