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Powder vs. Gravity: Why do tiny particles fly in the air, but sand and gravel don't?
In nature, powders behave very differently from sand and gravel, especially when faced with the effects of gravity. The phenomenon of small particles of powder floating in the air has triggered a lot of thinking about the structure and physical properties of matter. This article will explore how powder can overcome the constraints of gravity, while sand and gravel cannot fly so freely.
Powders are dry solids composed of very fine particles that flow freely when shaken or tilted.
The characteristic of powders is that their particles are very small, making them more susceptible to external forces during physical movement. Powders are used across many industries, from food processing such as flour, sugar, instant coffee, to pharmaceuticals, cosmetics and even color powders in industrial applications. In contrast, when we talk about sand and gravel, we are often referring to coarser particles whose weight and inertia make it difficult for them to flow under the action of gravity.
Mechanical properties of powders
Typically, powders have a wide range of mass densities, which is closely related to the structure of their particles. When vibrated or compressed, powders can become very dense and even lose their fluidity. In contrast, the mass density of sand and gravel will not change significantly. The different behavior can be traced back to the van der Waals forces between molecules, which enable tiny particles to attract each other. In tiny particles, this attraction becomes significant, causing the powder to form lumps; in sand and gravel, because the particles are large, their weight and inertia cannot be overcome by the weak van der Waals force, so there will be no particle aggregation. phenomenon.
The aggregation behavior of powders originates from weak van der Waals forces, which only play a dominant role when the particles are small and light.
Transport and Suspension
In the atmosphere, powders are transported in a manner that is distinctly different from coarse granular materials. Since tiny particles have less inertia, they tend to move with the airflow rather than in a straight line. This is why powders can be dangerous when it comes to inhalation. Because larger particles cannot easily pass through the body's defense system, powder particles can penetrate deep into the lungs, causing serious conditions such as silicosis.
The upward force provided by the random motion of air molecules and turbulence can counteract the downward effect of gravity, causing the powder particles to suspend in the air.
Coarse particles are too heavy and will fall back to the ground quickly. When the powder is disturbed, it forms large dust storms that span continents and oceans, and then forms sediments after settling. For example, the lunar regolith contains dust but no mudstone because there is a lack of wind and water influence.
The risks of powders
In addition, many industrially produced powders are combustible, especially some metals and organic substances, such as flour. Once ignited, the powder, due to its high surface area, will burn rapidly and produce an explosive reaction, which is quite high risk for factories doing this kind of work. Therefore, appropriate precautions must be taken during the handling of powders.
ConclusionPowders have a very high surface area, so once they burn they are likely to release energy in the form of an explosion.
Whether it is powder or sand, the behavior of these solid substances is deeply influenced by their physical properties. Tiny particles of powder can dance in the air, while sand and gravel are firmly bound by gravity. Wind or mechanical disturbances are key factors affecting the behavior of these particles. For this reason, the properties and applications of powders are still worth our in-depth exploration, and we should think further: In the future technological advances, how will the characteristics of powders and particles redefine our lives?
