Happy/Sad Balls

Introduction

Happy and Sad balls appear the same, but do they have the same properties? Bounce the balls, put them in the freezer, heat them in boiling water, compare their densities—observe the very interesting results.

Concepts

• Polymers
• Density

Materials

Safety Precautions

The materials used in this activity are considered nonhazardous. Wear protective eyewear. A Happy Ball can rebound in unexpected directions. Take care in bouncing the ball so that it does not hit anyone or anything with sufficient force to cause injury or damage. When dropping a Sad Ball from a high location, take care that it does not hit anything that can be damaged.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The glycerin and water solution may be rinsed down the drain with excess water according to Flinn Suggested Disposal Method #26b. 

Procedure

Bouncing Ball Activities

1. Drop a Happy Ball onto a hard surface (tile or cement floor preferred). Describe its behavior.
2. Repeat this procedure with a Sad Ball. Describe its behavior.
3. Repeat this procedure with both balls simultaneously, dropping them from a measured height. Measure how high they bounce.
4. Find a volunteer. Ask the subject if he/she can drop a ball and spin around and catch it before it bounces a second time. Demonstrate this using the Happy Ball. Switch the balls and hand the subject the Sad Ball.
5. Different formulations of Super Balls producing bright colors or translucent balls have different resiliencies. Obtain a number of different colored Super Balls and have a ball bouncing contest. Line up students and have them drop the balls at the same time to see which bounces higher.

1. Put both balls in a freezer or beaker of ice water. Drop both balls. Does their behavior change when they are cold? The Sad ball becomes even less elastic when frozen and will not bounce at all.
2. Boil both balls in a beaker of water. At about 85 °C, the Happy ball will float to the surface. When the water starts boiling, carefully remove the balls from the beaker and drop them onto the floor. The Sad ball will now bounce better than it did at room temperature.

1. Place the Happy and Sad balls in a tall beaker half full of water. Do the balls float or sink? (Note: Save the water for step 3). What does this tell about the density of the balls?
2. Place the Happy and Sad balls in a tall beaker half full of glycerin (glycerol). Observe. Glycerin has a specific gravity of approximately 1.3 g/mL.
3. Pour the water from step 1 into the beaker of glycerin containing the balls. Observe and compare the specific gravities before mixing the glycerin and water.
4. Mix the glycerin and water. Observe.

Discussion

The Happy Ball is a sphere having an extremely high resiliency factor, in excess of 90%, and a high coefficient of friction. These two qualities cause the ball to react in an extraordinary and unpredictable manner when bounced or struck. Thus, any spin applied to the ball will be accentuated when it rebounds from a hard surface. The Happy Ball is composed of about 100 parts polybutadiene, 0.5 to 15 parts sulfur vulcanizing agent, and 5 to 15 parts of filler such as hydrated silica, carbon black or lithium oxide. The sulfur vulcanizing agent is added in excess to products such as automobile tires (which contain about 3 parts sulfur) to produce cross-linking between the polybutadiene chains. Cross-linking gives the rubber its high resiliency. The ball is molded at a pressure of between 500 and 3,000 psi for 10 to 30 minutes at a temperature of 285–340 °F (140–171 °C). This produces the Happy Ball with the properties described above. In addition, it has been found that these balls also exhibit an ability to conserve energy. That is, when bounced, the ball will dissipate very little of its initial energy in the form of heat.

The Sad Ball may be composed of several different materials. Common materials used are poly(norbornene) and a poly(styrene–butadiene) block copolymer. These materials have a higher specific gravity than the Happy Ball, about 1.17 g/mL, and have low elasticity, and an ability to absorb energy. Thus, when the ball is dropped, it does not bounce. These properties also make the Sad Ball material useful for a number of applications. The poly(styrene–butadiene) co-polymer is used in automobile tires where it helps to absorb some of the bumps encountered on the highway. Polynorbornene is used in lining ballistic containers used by bomb squads (these look like big trash cans). Should a bomb explode, the rubber material will absorb a significant amount of energy.

References

Special thanks to David A. Katz, retired, Wilmington, DE, who provided Flinn Scientific with the instructions for this activity.