# Hands-on ActivityBuild Your Own Mobile

### Quick Look

Grade Level: 3 (3-5)

Time Required: 45 minutes

Expendable Cost/Group: US \$0.00

Group Size: 3

Activity Dependency: None

Subject Areas: Geometry

NGSS Performance Expectations:

### Summary

Student 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.
This engineering curriculum aligns to Next Generation Science Standards (NGSS).

### Engineering Connection

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.

### Learning Objectives

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.

### Educational Standards 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.

###### NGSS: Next Generation Science Standards - Science
NGSS Performance Expectation

3-PS2-1. Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object. (Grade 3)

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This activity focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts
Plan and conduct an investigation collaboratively to produce data to serve as the basis for evidence, using fair tests in which variables are controlled and the number of trials considered.

Alignment agreement:

Science investigations use a variety of methods, tools, and techniques.

Alignment agreement:

Each force acts on one particular object and has both strength and a direction. An object at rest typically has multiple forces acting on it, but they add to give zero net force on the object. Forces that do not sum to zero can cause changes in the object's speed or direction of motion. (Boundary: Qualitative and conceptual, but not quantitative addition of forces are used at this level.)

Alignment agreement:

Objects in contact exert forces on each other.

Alignment agreement:

Cause and effect relationships are routinely identified.

Alignment agreement:

###### International Technology and Engineering Educators Association - Technology
• Illustrate that there are multiple approaches to design. (Grades 3 - 5) More Details

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###### Massachusetts - Math
• Describe the two-dimensional figures that result from slicing three-dimensional figures, as in plane sections of right rectangular prisms and right rectangular pyramids. (Grade 7) More Details

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### Materials List

• hangers
• materials to attach objects to hangers that are either pliable, such as pipe cleaners, or that can tie, such as string, etc.

### Pre-Req Knowledge

An understanding of the concept of center of mass.

### Introduction/Motivation

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 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!

### Procedure

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

1. Divide the class into teams of three students each.
2. Hand out a display unit to each group along with at least two extra hangers.
3. 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.
4. Discuss the center of mass concept as students experiment to find balance using the various objects.
5. Discuss real-life engineerig examples in which the center of mass is important to the correct functioning of products and tools.

### Assessment

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.

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© 2013 by Regents of the University of Colorado; original © 2005 Worcester Polytechnic Institute