Rubber bounces back after being compressed due to its molecular structure. When compressed, the long molecular chains of rubber deform, storing potential energy. When the pressure is released, this energy is released, causing the rubber to bounce back.
Rubber is a polymer, a kind of long chain made up of thousands of smaller units called monomers. In the specific case of natural rubber, these units are primarily isoprene. These very long chains are arranged in a disordered manner, like tangled spaghetti. But what makes rubber so special is that these chains are linked together by types of chemical bridges called cross-links (cross-linked bonds). These bridges limit the movements while allowing enough freedom for the chains to temporarily deform, which accounts for its incredible ability to stretch or be compressed, and then quickly return to its original shape.
Rubber is elastic due to its long chain-shaped molecules twisted like spaghetti. These chains are mainly composed of polymers, which are giant molecules made up of repeating units. When you pull or compress rubber, you force these tangled and folded chains to unfold and stretch. As soon as you release, they spontaneously return to their original shape because they move freely but naturally prefer to revert to their coiled and disordered state, which requires less energy. This particular property mainly comes from rubber's ability to resist permanent structural changes; it likes to return to its normal state after deformation. It's exactly like when you pull on a rubber band: you stretch it, then whoosh, when you let go, it immediately returns to its original size and shape.
When you compress a piece of rubber, you provide it with mechanical energy. This energy does not disappear: it is temporarily stored as elastic potential energy within the long molecular chains of the material. These chains become compressed and deformed, just like stretched springs ready to release their energy. When you stop pressing, the rubber returns to its original shape and quickly releases this stored energy, resulting in its bounce. However, a small amount of energy is always lost as heat, which explains why the rubber never bounces as high as the height from which you initially dropped it.
The rebound of rubber primarily depends on the composition of the material: the purer and more homogeneous it is, the better it rebounds. The presence of additives or impurities alters the material's ability to return to its original shape after compression. The way the molecules are organized also plays a significant role; a well-bonded and flexible molecular structure facilitates better rebound. Temperature also comes into play: if it's too cold, rubber becomes rigid and rebounds less effectively; if it's too hot, it becomes soft and loses its elasticity. The duration of compression also changes the results; if pressure is maintained for a long time, the material recovers less efficiently. Finally, wear also matters: as rubber ages, it cracks, hardens, and gradually loses its rebound quality.
When rubber becomes colder, its molecules move less easily, making it more rigid and brittle. As a result, it loses a good part of its elasticity and bounces less well: this is typically what happens to a rubber ball left outside in the winter. Conversely, when it's hot, the molecules become more mobile, able to stretch easily and return to their original shape without issue. Rubber is therefore generally more flexible and bounces better at high temperatures. But be careful, as soon as the temperature gets too high, it softens significantly, and its elasticity eventually decreases. There is thus an ideal temperature range where rubber retains its best elastic properties.
The word "rubber" comes from the South American indigenous language "cao" (wood) and "ochu" (tears), literally meaning "tears of wood" in reference to the sap extracted from certain trees.
At low temperatures, rubber loses its flexibility and becomes rigid, which significantly reduces its ability to bounce.
Vulcanization, a process invented by Charles Goodyear in 1839, makes rubber more durable and resistant by creating chemical bonds between the molecular chains.
Natural latex used to produce rubber is primarily harvested from the rubber tree (Hevea brasiliensis), a tree native to South America.
Yes, by modifying the chemical formulation, adjusting the vulcanization process, or incorporating specific additives, it is possible to significantly improve the elasticity, resilience, and thus the rebound capacity of rubber.
Yes, as rubber ages, it can lose some of its elasticity. This phenomenon is related to chemical wear, prolonged exposure to sunlight (UV rays), oxidation, and extreme temperatures, which gradually degrade the molecular structure of the rubber.
At low temperatures, the rubber molecules lose their mobility, resulting in the material becoming stiffer. As a result, the ball absorbs energy less effectively, bounces less high, and is more prone to cracks or breakage in the event of an intense impact.
Natural rubber generally has superior elasticity compared to synthetic rubber due to its long and regular molecular chains. However, certain specific synthetic rubbers can be designed to exhibit equivalent or even superior elasticity characteristics based on industrial needs.
The quality of the rebound primarily depends on the chemical composition of the rubber, the degree of cross-linking between its molecules, and its density. The longer the flexible molecular chains in the structure, the better the object will bounce back after compression.
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