Physics of Fireworks Displays

1. Physics of Fireworks Displays

2. Basic Ingredients of Burning Fireworks • Oxidizing Agent (Nitrates, chlorates, perchlorates) – • provides O2 for burning e.g. potassium nitrate • Reducing Agent – burn the O2 to produce hot gases, • e.g. charcoal, sulfur • 3. Coloring Agent – Salts that give color to the burn • 4. Binder – binds the compound together, e.g. shellac • Desire to slow down the burning of fuel • Use larger grains of chemicals (250 -350 microns diameter)

3. Parts of a Firework Shell • Shell – main housing • Stars – pea or marble-sized units containing salts, powder. • metals, that create colors and patterns • 3. Black powder – provides the ‘crackle’ (75% potassium nitrate, • 15% charcoal, 10% sulfur, - an ancient recipe) • 4. Breaks - cardboard sections separate multiple stages • 5. Fuse – provides time delay

4. How is the firecracker shell fired ? • Shell is set in a steel or plastic mortar embedded in sand • An electronically ignited fuse sets off the charge • The hot gases from exploding powder propels the shell. • Time delay fuse needed to keep shell from exploding on the • ground

5. Mortar Launch System for a Fireworks Display Time for delay fuse to burn determines pattern of explosion: • Spherical – explosion occurs at apex of parabolic trajectory. • Parabolic (or umbrella) -up – explosion occurs on the way up. • Parabolic (or umbrella) -down – explosion occurs on the way • down

6. Where does the whistling come from ? • Black powder produces crackling sound. • Powder is packed into small cylinders open on one end. • Burning salts, chemicals produce enormous amounts of hot • CO2 rushing thru opening, causing a whistling sound.

7. Colorful Photons make colorful explosions Photon (E2-E1) E2 E1 Strontium Salts: 636 – 688 nm Fiery Red Barium Salts: 505 – 535 nm Bright Green Sodium ions: 589 nm Gold/Yellow Copper Salts: 420 – 460 nm Blue/Purple (expensive) Magnesium, Aluminum, Titanium : White

8. Examples of exploding Salts Shell exploding on the way up causes an ‘umbrella’ (really parabolic) pattern of burning salts.

9. A Simple Spherical Pattern Other Patterns: Double – Ring Pattern: Two rows of colorant pellet salts surrounding a central ‘bomb’ Heart Shaped Pattern: Glue Salt Pellets along Rim of a Heart-Shaped paper in the middle of a shell. Explosive charge is on top of it.