Physics of Fireworks Displays

Basic Ingredients of Burning Fireworks 1.Oxidizing Agent (Nitrates, chlorates, perchlorates) – provides O 2 for burning e.g. potassium nitrate 2.Reducing Agent – burn the O 2 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 ( microns diameter)

Parts of a Firework Shell 1.Shell – main housing 2.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

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

Mortar Launch System for a Fireworks Display Time for delay fuse to burn determines pattern of explosion: 1. Spherical – explosion occurs at apex of parabolic trajectory. 2. Parabolic (or umbrella) -up – explosion occurs on the way up. 3. Parabolic (or umbrella) -down – explosion occurs on the way down

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 CO 2 rushing thru opening, causing a whistling sound.

Colorful Photons make colorful explosions Strontium Salts:636 – 688 nmFiery Red Barium Salts:505 – 535 nmBright Green Sodium ions:589 nmGold/Yellow Copper Salts:420 – 460 nmBlue/Purple (expensive) Magnesium, Aluminum, Titanium : White Photon (E2-E1) E1E1 E2E2

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

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. A Simple Spherical Pattern