Rheology of glass and slow fluids · 1927–2026
Nine Drops in a Century
Strike a piece of pitch with a hammer at room temperature and it shatters into glossy shards like glass. Leave it in a glass funnel under gravity and it flows as a Newtonian liquid 230 billion times more viscous than water. Since 1927, the University of Queensland funnel has produced exactly nine drops.
The Queensland Rheometer
In 1927, Professor Thomas Parnell heated coal tar pitch and poured it into a sealed glass funnel, letting it settle for three years to release trapped air bubbles. In October 1930, he cut the stem, allowing gravity to begin its slow pull.
Adjust the time slider to track the mathematical evolution of the pitch meniscus through the 9.4 mm stem, from early bulging to critical capillary necking.
Deformation stage
Stage 3: Capillary Necking (Years 9–13)
Rayleigh-Plateau instability narrows the upper neck into a razor-thin filament of pitch, while the bottom bulb hangs suspended.
Chronology of Nine Falls
Until 1988, the physics lab in Brisbane operated without air conditioning. Scorching Queensland summers exceeded 30°C, lowering the pitch's viscosity and maintaining an average interval of eight years and two months per drop. When climate control was introduced at 21–22°C, formation times extended past twelve years.
Click any entry below to inspect details for each fall:
The Deborah Number and the Scale of Matter
The mechanical nature of pitch depends on the observation timescale. In rheology, this is quantified by the Deborah number (\(De = \tau / T_{\text{obs}}\)), the ratio between internal molecular relaxation time (\(\tau \approx 10^5\) seconds, roughly one day) and the observation window (\(T_{\text{obs}}\)).
Under a rapid hammer blow (\(T_{\text{obs}} \approx 1\text{ ms}\)), the Deborah number exceeds \(10^8\), causing rigid glassy fracture. Under gravitational drain across a decade (\(T_{\text{obs}} \approx 3 \times 10^8\text{ s}\)), the Deborah number drops to \(0.0003\), allowing the molecular network to flow as a true fluid.
| Substance | Dynamic Viscosity (\(\text{Pa}\cdot\text{s}\)) | Drain Time for 100 ml (5 mm nozzle) | Mechanical Behavior |
|---|---|---|---|
| Liquid Helium (He II, 2 K) | 1.0 × 10⁻⁵ | 0.001 seconds | Superfluidity with near-zero internal shear resistance |
| Pure Water (20°C) | 1.0 × 10⁻³ | 0.1 seconds | Universal baseline for everyday fluidity |
| Olive Oil (20°C) | 8.4 × 10⁻² | 8.4 seconds | 84 times more viscous than water |
| Pure Honey (20°C) | 1.0 × 10¹ | 16 minutes, 40 seconds | 10,000 times more viscous than water |
| Toothpaste (at rest) | 1.0 × 10² | 2 hours, 46 minutes | Bingham plastic: flows only under applied mechanical stress |
| Coal Tar Pitch (Parnell, 20°C) | 2.3 × 10⁸ | 729 years | 230 billion times more viscous than water; shatters on shock |
| Glacier Ice (-5°C) | 1.0 × 10¹³ | 31.7 million years | Slow plastic creep carving mountain valleys |
| Earth's Upper Mantle | 1.0 × 10²¹ | 3,170 billion years | Solid-state thermal convection driving continental drift |
The Pitch Clock of Your Lifetime
How much has the Queensland funnel moved since the year you were born? Enter your birth year to calculate how many drops have fallen in your lifetime.
2 drops
In your 31 years of life, the University of Queensland pitch funnel has dropped exactly 2 times. Since the last drop in April 2014, Drop 10 has been stretching continuously for the past 12 years.
Method Note & Sources
Viscosity measurements and funnel geometry are documented in R. Edgeworth, B. J. Dalton, and T. Parnell, “The pitch drop experiment”, European Journal of Physics 5 (1984): 198–200, and verified against University of Queensland laboratory logs maintained by John Mainstone and Andrew White (2014–2026). Volumetric discharge is calculated via the Hagen-Poiseuille equation for laminar flow: \(Q = \frac{\pi \rho g h r^4}{8 \eta L}\), with stem radius \(r = 4.7\text{ mm}\), stem length \(L = 30\text{ mm}\), and pitch density \(\rho = 1,100\text{ kg/m}^3\).