After this activity, students should be able to:

• Understand that engineers and artists use the same concepts of forces to create a design.
• Identify careers that use concepts of forces and art to design and create things for society.
• Identify that gravity is the primary force acting on a mobile.
• Understand the relationship between forces and mobiles.
• Understand artist sometimes use skills they learned in engineering studies to complete beautiful works of art.
• Use elements of art, principles of design and styles of art to communicate their understanding of forces.
• Experiment with materials, tools, techniques and processes that enhance communication of ideas through art.
• Demonstrate understanding of and proficiency with basic addition, subtraction, multiplication and division facts without the use of a calculator.
• Practice using numbers to describe balanced forces in example math problems.
• Identify works of art designed by engineer Alexander Calder.

What are forces? How do they impact our lives? (Possible answers from students: Gravity, forces acting on bridges, buildings and people.)

The mobile was invented by Alexander Calder, who was born in 1898 in Pennsylvania to a family of artists. As a young child, Alexander created his own toys including small metal animals. Have you ever made your own toy or game? Alexander Calder was educated as a mechanical engineer in college, and later became a painter. He used his knowledge of engineering principles to create beautiful works of kinetic (moving) art (see Figure 2). After graduating, Calder worked in Paris creating sculptures.

While working in Paris, Alexander experimented with structures that could move randomly when propelled by wind or air currents. The movement of air currents is called convection. When these structures are hanging freely in the air, they are called mobiles (see Figure 1). When Calder designed a mobile he started with the smallest sections first and carefully connected each piece, balancing the weights as he went along. What is one force that we consider when balancing two weights? (Answer: Gravity) What happens if two sides on a mobile are not balanced? (Answer: The mobile hangs to one side, the heavier side.) Calder used his knowledge of engineering concepts related to force to help him create level and balanced sculptures.

Figure 2. Aluminum Leaves, Red Post by Alexander Calder, c. 1941. A free-standing mobile made of sheet metal, wire, wood and paint. click for copyright

Figure 3. A wind-driven, kinetic sculpture in Colorado Springs, CO. click for copyright

Figure 4. A wind-driven kinetic sculpture in Vail, CO. click for copyright

Today, many artists create amazing mobiles and kinetic sculptures that are moved by the forces of the wind (see Figures 2-4). Artists also must take other forces, such as gravity, into account as they design their works of art. Both engineers and artists must understand how different forces affect the things they create. Think about the list of forces we discussed earlier.

Before the Activity

With the Students

1. Warm students up with a discussion question and some brainstorming. Ask students: What are forces? (Answer: A force is any push or pull on an object. Examples include gravity, wind, water.) Brainstorm with students on how forces affect our lives.
2. Have the student teams use the paper, markers and scissors to design 6-10 cut-out figures to attach to the mobile. These can be varying shapes and sizes (see Activity Extensions section for an idea).
3. While student teams are finishing, ask them some questions to keep them engaged: What is convection? (Answer: The movement of air currents.) Define a mobile? (Answer: A hanging or suspended structure that moves randomly when propelled by air currents.) What is one force we consider when balancing two weights (Answer: Gravity)
4. Have the students prepare their paper figures by punching a hole into each and attaching a string (or needle and thread). Each figure should have a string for hanging it.
5. Have students hang their figures from the ends of straws by tying the string from the figure to the straw.
6. Have students attach the straws to one another until their mobile is balanced (see Figure 5). They may choose to cut the straws in half or leave as is. They should take into account the center of mass and downward forces while connecting the mobile. The students should feel free to create as many or as few layers as they wish.

Figure 5. Example student activity — a balanced mobile. (The straws are in yellow.) click for copyright

7. Have each student team present their designs to the class.
8. Have students complete the Giant Mobile Math Worksheet.

• Students should be careful handling scissors.
• If needle and thread is used, students should be careful when handling the needles.

Pre-Activity Assessment

Activity Embedded Assessment

Post-Activity Assessment

• For younger students (grades 3-4) who may have trouble balancing the straws, follow the attached Alternative Mobile Design. In this easier construction method, student attach their cut-out shapes to a plate instead of straws.
• For younger students (grades 3-4), simplify the multiplication and division problems on the Mobile Math Worksheet to include lower-level division.