Objective:
– To illustrate how the coefficient of restitution of a ball effects height of bounce.
Apparatus:
- “unhappy” ball made of norsolex (Norbornene polymer)
- “happy” ball made of neoprene
- meterstick (optional)
Method:
The two balls look alike but when dropped onto a hard surface the neoprene ball rebounds to almost 70 % of its initial height whereas the norsolex ball hardly bounces at all. The properties of the two materials (as stated on the manufacturer’s specification sheet) are as follows:
|
Property
|
Neoprene
|
Norsolex
|
| Tensile strength (kg f/cm2) |
205
|
124
|
| Stretch (%) |
370
|
550
|
| Hardness (JIS A) |
63
|
32
|
| Restitution elasticity (%) |
53
|
3
|
| Specific gravity |
1.39
|
1.25
|
– If one wishes they can use a meterstick to measure the drop and rebound height of the neoprene ball.
Comments:
The manufacturer’s information sheet states the following:
“The “Unhappy ball” is made of rubber called Norbornene polymer (brand name: Norsolex) which possesses excellent impact absorption properties. The rubber has great internal absorption of inputted energy and is able to dampen impact from a colliding object without giving the object a reaction force. It has the advantage whereby little resonance can be caused to occur by external vibrations. It can be processed in a similar manner to that of ordinary rubber, and sheets made of the material are utilized in a lot of applications…..
Range of Uses:
- As damping material for protection of conveyor mechanisms, stoppers for precision location of articles conveyed, and shock absorbers (in place of pneumatic and hydraulic types).
- Padding materials for prevention of things dropped from being scattered and for the reduction of fatigue on legs and loins.
- Material for minimizing resonance on audio equipment prevention of speaker howl. Insulation of external vibration to player units.
- Low hardness rubber roll material rolls for printing.
- Footwear sole material for the reduction of heel strike.
- Industrial use gaskets and packing.
- Sporting goods gloves, mitts, and supporters.”
Collisions Demo: Happy and Sad Balls
– Video Created at Utah State University by Professor Boyd F. Edwards and assistants.