Many people are not even aware that there are many objects and things around us that have amazing properties. In this article, let’s discuss the hardness of some materials and the interesting results that are derived from these properties.
In 1994, a big earthquake hit near Los Angeles, killing 57 people and injuring more than 5,000. The property damage reached an incredible $20 billion. Earthquakes like these make us wonder. How solid is the ground beneath our feet? What does the concept of hardness even mean?
Coal tar appears to be hard, but it is not. In fact, it is a very viscous liquid, i.e., it is liquid. Viscosity is a measure of resistance to flow. Olive oil is about 100 times more viscous than water, and honey is 100 times more viscous than oil. The viscosity of pitch is 230 billion times that of water. The University of Cleveland is conducting the world’s longest experiment on peck. In 1927, pitch was placed in a funnel. Over 90 years, only nine drops fell from it. No one was present when the droplet fell. In 1988, the keeper of the experiment, John Mainston, was close to seeing the drop fall. He left the room to pour himself some tea and missed the cherished moment. You can watch this experiment online, but since the last drop fell in 2014, it’s unlikely you’ll get to see the coveted drop in the coming years.
Another substance that is a viscous liquid is glass. Glass is unusual in that it is an amorphous body. Silicon dioxide molecules do not form an ordered structure. Glass cools so rapidly that in the transition from liquid to “solid” state, the molecules do not have time to line up in an ordered crystalline structure. Visually, what makes glass solid is the atoms or molecules that are so strongly chemically bonded to each other that they cannot slip next to each other.
However, the absence of an ordered crystal structure makes glass still liquid, even when it is in a visually solid state. It is because glass is actually liquid that you can clearly see in the window frames in old houses, where the windows have been standing for decades, that the glass is thinner at the top than at the bottom. This is due to the fact that some of the glass over the long years is already glass from the top down. Therefore, in such houses, the windows rattle in their frames, because at the top they are already thinner than the gap prepared for them. Sometimes this effect is so noticeable that there is even a gap at the top.
Let’s move on. What do we know about the interior of the Earth? Under the Earth’s crust is the mantle, which is responsible for tectonic plate movements and earthquakes. Is it solid or liquid? We can never see the mantle directly, but we can observe lava, which is a red-hot rock. We can imagine that the mantle is very similar to it. The mantle must be liquid because it needs to flow, right? Actually, no, because the mantle is a solid body. Earthquake-moving waves can propagate through the mantle, but those waves can’t move through liquids, which is proof of its solidity. So how does solid rock flow? The answer lies in the non-ideality of crystals, which may be missing a few atoms. The viscosity of the mantle is similar to that of glass, only a few orders of magnitude higher. The mantle becomes like a liquid, but only during geological time intervals. Peck is a liquid that can flow so slowly that it appears to be a solid. And the earth’s mantle is a solid that behaves like a liquid if you wait long enough.
Hardness and plasticity are not absolute, but only relative. And all bodies are actually both liquid and solid at the same time. When there is tremendous mass and force in a case, the difference loses meaning. The solid definitions we create for ourselves lead to misconceptions and viscous rumors.