20. Demos for special occassions

• 20.1. Spectacular spectrum
• 20.2. Making a slanting tower stacking blocks
• 20.3. Magic with pendulums
• 20.4. Falling candle
• 20.5. Boiling without heating in a vacuum
• 20.6. Stick on wine glass
• 20.7. Cloud formation
• 20.8. Optics with LEDs
• 20.9. Spinning circles in a wine glass
• 20.10. Pulling a spool
• 20.11. Implosion