Balancing Acts
By John Cowens

Creating, building and assembling objects that balance is a lot of fun and easy to do. The following activities will help stimulate students to be creative in designing, building and assembling simple artistic sculptures requiring balance (by locating the center of gravity) and varying amounts of mass.

Act I: A popsicle stick
Materials (for the teacher):

• 20-22 gauge uninsulated wire


• wire cutters

Materials (for each student):

• one popsicle or craft stick


• 8" length of 20-22 gauge soft wire


• two standard-size hex nuts

Please note that the stiff wire used in this activity can have sharp points. To prevent injuries from occurring, be sure that your students are not crowded together. You can bend a 1/2" hook on each end of your students' wires ahead of time to avoid this concern.

Procedures:

1. Using the wire cutters, cut the wire to 8" lengths for each student.
2. Optional: bend each wire 1/2" from each end to form two hooks.
3. Mark each popsicle stick about 1.5" (3.5 cm) from one end.
4. Bend the wire approximately in two equal halves.
5. Wrap the wire around the stick about two times at the pencil mark so that the two ends of the wire are the same length.
6. Curve the wire ends down and away from the long end of the stick.
7. Add a hex nut to the end of each wire and bend the hook shut so the weight will not easily fall off.



8. Try balancing the stick on a fingertip. If it tips over and falls, bend one or both wires slightly in or out, and observe how it balances. Keep moving the wires to counter the way the popsicle stick tips and falls off until the center of gravity is on the fingertip.
9. Instead of holding the balanced object on your fingertip, tape a pencil flat on a tabletop so that the the eraser sticks out from the table. Now balance your stick on the eraser. Make minor adjustments by slightly bending the wires until perfectly balanced.

Centers of gravity
Trying to balance a stick on one end with no other mass is difficult because the stick's center of gravity is well above the resting point at its lower end. When wire and hex nuts are added properly, the center of gravity is relocated to a point below the lower end of the stick.

If the wire arms are bent farther down, nearly together, and below the lower end of the stick, the center of gravity is lowered even more. The stick still balances but is not very stable. If you bend one wire upward and outward, the center of gravity of the whole system is redistributed and causes a tilt or rotation of the whole system. If the center of gravity moves to a point above the lower end of the stick, the whole system may rotate off its resting place. Adding more mass to the arms in the lower position brings the center of gravity down and makes the stick easier to balance. Reducing the amount of mass from the lowered arms raises the center of gravity, making the stick difficult to balance.

Act II: A STYROFOAM™ ball
Materials:

• a 1" or 2" STYROFOAM ball (2.5 cm or 5 cm)


• one drinking straw cut into two equal lengths


• a toothpick


• clay


• a pencil with a good eraser

Procedures:

1. Push the toothpick halfway into the STYROFOAM ball. Try to balance the ball in a vertical position with the end of the toothpick on your fingertip.
2. Insert the two short straws into the ball at 45-degree angles to the straw. The straws and toothpick should be in a straight line.
3. Add a small clay ball approximately 1 cm in diameter to the ends of the straws.



4. Now try to balance the STYROFOAM ball on the pencil's eraser as described in Step #1.

You can also have your students make a mobile using dowel rods, wire hangers, tree branches, plastic straws, fishing line or kite string. Cut the sticks (or wire) in various lengths and have each student collect or create items to place as weights on their mobile.

John Cowens teaches sixth grade at Fleming Middle School in Grants Pass, OR.

March 2007, Vol.37, No.6