Is Glass a Liquid?

TL;DR

Earth's mantle, pitch, and glass have the appearance of solids but exhibit fluid-like properties due to their high viscosity.

Transcript

In 1994, a massive earthquake shook the Northridge suburb of Los Angeles, killing 57 people and injuring over 5000. The cost of damages was in excess of $20 billion. It's earthquakes like this one that make us question just how solid is the earth beneath our feet, and what does it mean to be solid anyway? At first glance, pitch looks like a solid, ... Read More

Key Insights

• 💐 Pitch, a highly viscous liquid mistaken for a solid, demonstrates the concept of resistance to flow.
• ⏳ Glass does not flow over time, but variations in thickness are due to the challenges of manufacturing uniform glass objects.
• ✋ Earth's mantle, under extreme pressure and high temperatures, remains solid and behaves like a fluid over geological timescales due to crystal imperfections.
• ⏳ Misconceptions about the fluidity of the Earth's core and glass flowing over centuries lead to popular misunderstandings.
• 💦 Viscosity determines the behavior of liquids, with substances like pitch having significantly higher viscosity than water or honey.
• ☠️ The University of Queensland's pitch experiment, ongoing for nearly 90 years, reveals its extremely slow flow rate.
• 👋 Propagation of shear waves through the Earth's mantle demonstrates its solid nature, despite its high temperature and pressure conditions.

Questions & Answers

Q: How does viscosity affect the behavior of liquids like pitch and glass?

Viscosity determines a liquid's resistance to flow, with high viscosity substances like pitch appearing solid but flowing very slowly, while glass is difficult to mold with uniform thickness due to its varying viscosity.

Q: Is the Earth's mantle a solid or a liquid?

Despite being hot and under immense pressure, the Earth's mantle is a solid. This is evidenced by the propagation of shear waves through the mantle and the absence of seismic waves passing through liquids.

Q: Why does glass not flow over time, as previously believed?

Glass does not flow or thicken over time, as evidenced by the survival of ancient glass objects. The misconception arises from the difficulty in creating glass with uniform thickness, leading to thicker sections being positioned at the bottom.

Q: How do crystals in the Earth's mantle allow for rock to behave like a fluid?

Imperfections in crystals allow neighboring atoms to fill gaps, causing the solid rock in the mantle to exhibit fluid-like behavior over geological timescales.

Summary & Key Takeaways

• Pitch, a substance that appears solid, is actually a highly viscous liquid at room temperature and exhibits resistance to flow.

• Glass, despite rumors of flowing over time, is a solid material that is difficult to make with uniform thickness.

• Earth's mantle, although hot and under extreme pressure, remains solid and behaves like a fluid over geological timescales due to the movement of atoms within crystals.