To find out more about the podcast go to The surprising enigma of slippery ice.
Below is a short summary and detailed review of this podcast written by FutureFactual:
Why Is Ice Slippery? Unraveling the Theories Behind Ice Friction
Introduction: The Ice Slippery Mystery in the Real World
In this Scientific American Science Quickly episode, the host takes listeners from a crowded lower Manhattan ice rink to the Cortina Curling Olympic Stadium to explore a deceptively simple question: why is ice slippery? The conversation frames ice slipperiness as a scientific riddle with broad implications, from Olympic performance to global energy efficiency. The piece emphasizes that the traditional schoolbook answer is incomplete and that multiple physical processes may contribute to slipperiness.
Three Leading Theories of Ice Slipperiness
The episode reviews three long-standing ideas. The Thompson pressure-melting hypothesis posits that load on ice lowers its melting point, creating a thin lubricating layer. The Bowden frictional-heating theory suggests that frictional heat at the contact surface melts the ice, reducing friction and enabling slip. A third hypothesis proposes a pre-melted boundary layer, a structural, boundary region where ice and water meet, producing a liquid-like layer even without bulk melting. The hosts emphasize that each theory has limitations and that computer simulations hint at a combined effect rather than a single mechanism at work.
"as we walk or skate on ice, the friction we create heats and melts the surface." - Frank Bowden
Experiments and Findings: Temperature Matters
The discussion turns to experimental work led by Daniel Bond, a physicist at the University of Amsterdam. By measuring friction across a wide temperature range, the team found that friction decreases from very cold temperatures to about -7 °C, then increases as ice nears the melting point. This reveals an optimum temperature for skating and shows that slipperiness precedes friction, challenging purely friction-based explanations.
"You would need 10 elephants resting on a single skate. In order to get a decent amount of melting due to the pressure." - Daniel Bond
The Amorphous Layer Theory: A New Boundary Layer
Beyond the three classics, the episode introduces a newer idea: an amorphous layer at the surface, a liquid-like boundary that is not quite water and not quite ice. Paulina Ruinska explains that this layer forms due to structural differences at the boundary, creating a disordered surface that could facilitate slipping. The concept is tied to recent discussions in Physical Review Letters by Martin Meiser and colleagues, who study how misaligned ice crystals can amorphize at very low temperatures and how the surface water can become more liquid-like under certain conditions.
"they call it like an amorphous layer. So it's a layer that's liquid-like, but it's not really liquid because it's very thin." - Paulina Ruinska
Implications and Broader Significance
Understanding why ice is slippery has practical consequences beyond ice rinks. If friction is not the sole culprit, researchers may uncover principles applicable to reducing energy loss due to friction in trains, tracks, and other moving parts, potentially contributing to significant energy savings. The discussion also notes a national pride angle for Dutch speed skaters, but emphasizes that the quest for the underlying physics could drive advances in materials science and engineering across many systems.
"There is an optimum temperature for ice skating, which is -7 °C." - Daniel Bond
