Rubber-like elasticity

Japanese: ゴム状弾性 - ゴムじょうだんせい

Also known as rubber elasticity. A unique elasticity exhibited by rubber and similar substances (elastic sulfur, various synthetic rubbers, etc.). These substances are extremely stretchable (Young's modulus is about 1/100,000th of that of normal solids) and can stretch to several times their original length, but when the temperature is raised under a constant load, their length shrinks, and adiabatic stretching generates heat (normal solids endure heat). This is because the causes of elasticity are fundamentally different; in normal solids, stretching changes the atomic spacing and increases potential energy (internal energy), generating tension as they try to return to their original low-energy state, whereas in rubber-like substances, the entropy associated with the thermal motion of the chain polymers that make up the substance decreases as they are stretched, generating tension as they try to return to their original high-entropy state. The former is also called energy elasticity, and the latter entropy elasticity. → Joule-Thomson effect

Source : Heibonsha Encyclopedia About MyPedia Information

Japanese:

ゴム弾性とも。ゴムおよび類似の物質（弾性硫黄，各種合成ゴム等）が示す特異な弾性。これらの物質はきわめて伸びやすく（ヤング率が普通の固体の約10万分の１）またもとの長さの数倍も伸びるが，特に一定荷重のもとで温度を上げると長さが縮み，断熱的伸びでは発熱する（普通の固体では吸熱）。これは弾性の原因が本質的に異なるためで，普通の固体では伸長により原子間隔が変化し位置エネルギー（内部エネルギー）が増加するため，エネルギーの低いもとの状態にもどろうとして張力を生じるのに対し，ゴム状物質ではそれを構成する鎖状高分子の熱運動に関連するエントロピーが伸長により減少するため，エントロピーの大きいもとの状態にもどろうとして張力を生じる。前者をエネルギー弾性，後者をエントロピー弾性ともいう。→ジュール=トムソン効果

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