In 1994, a powerful earthquake hit the Northridge area of Los Angeles. It was a tragic event, causing 57 deaths and injuring over 5,000 people. The damage was so extensive that it cost more than $20$ billion to repair. Events like this make us wonder about the ground we walk on and what it really means for something to be solid.
Pitch might look like a solid, but it’s actually a very thick liquid at room temperature. Viscosity is a measure of how much a liquid resists flowing. For example, olive oil is about 100 times thicker than water, and honey is 100 times thicker than olive oil. Pitch, however, is incredibly thick, with a viscosity of $2.3 times 10^{11}$ times that of water!
At the University of Queensland in Australia, there’s a famous experiment with pitch that started in 1927. A blob of pitch was placed in a funnel, and in nearly 90 years, only nine drops have fallen—about one drop every ten years. Interestingly, no one has ever seen a drop fall. In 1988, someone almost witnessed it, but they stepped out for a cup of tea at the crucial moment!
Some people mistakenly think glass is a liquid because old stained glass windows in churches are thicker at the bottom. This led to the belief that glass flows over time. However, studies of ancient telescopes and windows show no evidence of this happening. The thickness difference is due to the difficulty in making glass evenly thick, so the thicker part was placed at the bottom.
Glass is actually an amorphous solid. This means its molecules are not arranged in a neat, regular pattern like in crystals. When glass cools quickly from a liquid to a solid, its molecules don’t have time to form a structured lattice. Unlike liquids, the atoms in glass are tightly bonded and can’t move past each other at room temperature.
Below the Earth’s crust is the mantle, which is important for plate tectonics and earthquakes. Many people think the mantle is made of molten rock, like lava, but it’s actually solid. We know this because shear waves from earthquakes can travel through the mantle, and these waves can’t move through liquids.
The mantle stays solid due to the immense pressure it is under. However, over long periods, it behaves like a fluid because of tiny imperfections in its crystal structure. Its viscosity is similar to that of glass, making it seem rigid in the short term.
The way pitch and the Earth’s mantle behave challenges our strict definitions of solids and liquids. As geologist Grove Karl Gilbert said, “Rigidity and plasticity are not absolute terms, but relative.” This means we should be open to rethinking how we understand materials and their states.
In conclusion, the lines between solids and liquids aren’t always clear. By being flexible in our understanding, we can better appreciate the complex nature of the materials that make up our world.
Imagine you are a scientist studying earthquakes. Create a simple model using a tray filled with sand and small blocks to represent buildings. Shake the tray gently to simulate an earthquake. Observe how the “buildings” react. Discuss with your classmates how the ground’s solidity affects the stability of structures during an earthquake.
Gather different liquids such as water, olive oil, and honey. Pour each liquid down a sloped surface and time how long it takes for each to reach the bottom. Compare your results and calculate the relative viscosity of each liquid. Discuss why pitch, with its extremely high viscosity, behaves like a solid over short periods.
Use a magnifying glass to examine different types of glass objects, such as a windowpane and a glass bottle. Discuss the concept of amorphous solids and how the molecular structure of glass differs from that of crystalline solids. Consider why glass is often mistaken for a liquid and how its structure supports its solid state.
Create a model of the Earth’s layers using clay or playdough. Use different colors to represent the crust, mantle, and core. Discuss how the mantle, though solid, can flow over long periods due to its viscosity. Relate this to the movement of tectonic plates and the occurrence of earthquakes.
Organize a debate in class about whether certain materials, like pitch and glass, should be classified as solids or liquids. Use evidence from experiments and research to support your arguments. Reflect on how this debate helps us understand the complexity of material states and the importance of flexibility in scientific definitions.
Earthquake – A sudden shaking of the ground caused by the movement of the Earth’s tectonic plates. – During the earthquake, the ground shook so violently that it caused buildings to sway.
Pitch – The perceived frequency of a sound, which determines how high or low it sounds. – The pitch of the sound increased as the frequency of the waves became higher.
Viscosity – A measure of a fluid’s resistance to flow. – Honey has a higher viscosity than water, which is why it flows more slowly.
Liquid – A state of matter that has a definite volume but no fixed shape, allowing it to flow. – Water is a liquid that takes the shape of its container.
Solid – A state of matter characterized by particles arranged in a fixed structure, giving it a definite shape and volume. – Ice is a solid form of water, with molecules arranged in a rigid structure.
Mantle – The layer of the Earth located between the crust and the core, composed of silicate rocks rich in magnesium and iron. – The mantle is responsible for the movement of tectonic plates due to convection currents.
Glass – A hard, brittle substance typically made from silica, used in windows and bottles. – When cooled rapidly, molten glass forms a solid without a crystalline structure.
Atoms – The basic units of matter, consisting of a nucleus surrounded by electrons. – Atoms combine to form molecules, which make up the substances we see around us.
Crust – The outermost layer of the Earth, composed of rock, that forms the continents and ocean floors. – The Earth’s crust is divided into several large and small tectonic plates.
Tectonics – The study of the movement and interaction of the Earth’s plates, which causes earthquakes, volcanic activity, and mountain building. – Plate tectonics explains how continents drift and why earthquakes occur along fault lines.
