Physics Dept. Demonstration Manual

DMP06 - Coefficient of Restitution - "Happy and Unhappy Balls"

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 ball 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

  1. 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).

  2. Padding materials ... for prevention of things dropped from being scattered and for the reduction of fatigue on legs and loins.

  3. Material for minimizing resonance on audio equipment ... prevention of speaker howl. Insulation of external vibration to player units.

  4. Low hardness rubber roll material ... rolls for printing.

  5. Footwear sole material ... for the reduction of heelstrike.

  6. Industrial use ... gaskets and packing.

  7. Sporting goods ... gloves, mits, and supporters."