======Happy and Sad Balls======


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**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
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**Categories:** {{$demo.categories}}
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**Alternative titles:** Elastic and Inelastic Collisions
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====Summary====                   
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====Procedure====  
  - Obtain a "happy" ball (neoprene rubber) and a "sad" ball (norbornene polymer).  
  - Hold both balls at the same height.  
  - Drop them simultaneously onto a hard surface.  
  - Observe that the happy ball bounces high while the sad ball barely bounces.



====Links==== 
Collisions Demo: Happy and Sad Balls - Physics Demos: 
{{youtube>lubaukB6B34?}}\\

Happy & Sad Balls - SMU Physics: 
{{youtube>v1k0lWOYOnw?}}\\

📄 Happy & Sad Balls - SMU Physics: [[https://demos.smu.ca/demos/mechanics/139-happy-sad-balls]]\\

====Variations====
  * Try dropping the balls from different heights to compare rebound behavior.  
  * Use additional balls made from other materials (e.g., steel, glass, plastic) to compare energy transfer.  
  * Roll the balls into a wall to observe horizontal collisions.



====Safety Precautions====  
  * If using heavy or very hard balls for comparison, caution is needed to prevent injury or damage.




====Questions to Consider====
  * Why does the happy ball bounce higher than the sad ball? (Because less energy is lost to deformation and heat, making the collision more elastic.)  
  * What happens to the energy that doesn’t go into bouncing the sad ball? (It dissipates as heat, sound, and internal deformation of the material.)  
  * How does the coefficient of restitution describe these collisions? (It quantifies how much kinetic energy is conserved; a higher value means a more elastic collision.)  
  * Can a ball ever bounce higher than the height it was dropped from? (No, because that would require energy gain, which violates conservation of energy.)