Happy and Sad Balls

Title: Happy and Sad Balls

Author(s): Patricia Gonzalez

Principles Illustrated:

macromolecules

polymers

conservation of energy

transfer of energy

Standards:

Questioning Script

Prior knowledge & experience:

Root questions:

1. What is the difference in behavior of the two balls when dropped?

2. Before the balls were dropped, how did their energies compare?

3. How did the energy compare after they hit the floor?

4. Which ball lost more energy?

5. Where did the energy go?

6. Explain how this effect would be different on the moon.

Target response:

Neoprene( the Happy ball ) is the trade name for polychloroprene. It is the softer of the two balls and bounces well like a superball. It has high resilience and dissipates little of its kinetic energy as heat or sound when bounced. In Physics terms, we say it has a high coefficient of restitution or a good bounce. An important use for this product is that it is used for swimwear. If you are a swimmer, scuba diver, or water skier, it is used for wet suits because it tends to hold heat.

Norsorex ( the Sad ball ) is the trade name for polynorbornene. It also is known as Noene, Sorbothene, and Astrasorb. It has low resilience and tends to absorb or dampen the kinetic energy of the bounce. In Physics terms we call this a very low coefficient of restitution or no bounce. It produces a small increase in its temperature and the characteristic "thud" sound upon impact. It too is used as clothing in the form of artificial leather as well as sound insulation, damping, and seals and gaskets. Elastomeric and viscoelastic solid polymers are soft rubbery solids which maintain their shock absorbing properties at higher impact speeds than foam. Because they are 100% solid, they are far stiffer than foams and a large fraction of the peak impact force is still transmitted through the material. The only material suitable for making body armor is polynorbornene more commonly called by its trade name Norsorex. This is a dense, closed cell foam that has the ability to spread impact forces over a wide area. The most common "Happy / Sad" balls currently being marketed are: ( the Happy ball ) is the trade name for polychloroprene. It is the softer of the two balls and bounces well like a superball. It has high resilience and dissipates little of its kinetic energy as heat or sound when bounced. In Physics terms, we say it has a high coefficient of restitution or a good bounce. An important use for this product is that it is used for swimwear. If you are a swimmer, scuba diver, or water skier, it is used for wet suits because it tends to hold heat.

The Happy ball is common neoprene and rebounds very well. The Unhappy ball is norborene polymer rubber and possesses excellent impact absorption properties which allow it to hit the floor like a rock. Although both balls are identical in shape, the Unhappy ball has a bounce of almost zero while the Happy ball rebounds very well under standard 10-30°C conditions.°C conditions.

Polymers such as elastomers have a rather unique property referred to as the glass transition temperature or Tg. This property is the temperature in which the material changes from a hard, glassy crystalline material to a soft, rubbery, amorphous material. The two balls have different glass transition temperatures and that partially accounts for the reason they bounce at different levels. With the so-called Happy ball, its glass transition temperature of -42°C makes it highly elastic at temperatures above its glass transition temperature and therefore has a higher level of rebound vs bounce rate. (The glass transition temperature for the Sad ball is 35°C.) Upon cooling the Happy ball below its glass transition temperature with liquid Nitrogen (LN2 ), the ball becomes less elastic and the bounce rate is also less. Heating this ball in boiling water has no appreciable effect as it basically bounces the same as it did at room temperature.

The so-called Sad ball has a glass transition temperature of 35°C and this makes it very non-elastic and therefore does not bounce very high. It actually is sometimes characterized as falling "like a rock" or making a thud-like sound. Upon cooling it with either ice cubes in a Styrofoam chest, dry ice,or LN2, the ball bounces even less than at room temperature. Heating the ball in boiling water makes the ball considerably more elastic and will bounce to perhaps one-third that of the Happy ball bounce.

Common Misconceptions:

Photographs and Movies

References

http://www.polymerambassadors.org/happyandsad.pdf

http://www.evilmadscientist.com/article.php/HappySad