physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which rel ...

, the

elastic potential energy Elastic energy is the mechanical potential energy stored in the configuration of a material or physical system as it is subjected to elastic deformation by work performed upon it. Elastic energy occurs when objects are impermanently compressed, ...

gained by a wire during elongation with a tensile (stretching) force is called strain energy. For linearly elastic materials, strain energy is: :

U = \frac 1 2 V \sigma \epsilon = \frac 1 2 V E \epsilon^2 = \frac 1 2 \frac V E \sigma^2

where is stress, is strain, is volume, and is

Young's modulus Young's modulus E, the Young modulus, or the modulus of elasticity in tension or compression (i.e., negative tension), is a mechanical property that measures the tensile or compressive stiffness of a solid material when the force is applied ...

: :

E = \frac \sigma \epsilon

Molecular strain

In a

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...

, strain energy is released when the constituent

atoms Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas ...

are allowed to rearrange themselves in a chemical reaction.''March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure,'' Michael B. Smith & Jerry March, Wiley-Interscience, 5th edition, 2001, The external work done on an elastic member in causing it to distort from its unstressed state is transformed into strain energy which is a form of potential energy. The strain energy in the form of elastic deformation is mostly recoverable in the form of mechanical work. For example, the

heat of combustion The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The ''calorific value'' is the total energy rele ...

cyclopropane Cyclopropane is the cycloalkane with the molecular formula (CH2)3, consisting of three methylene groups (CH2) linked to each other to form a ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane itself i ...

(696 kJ/mol) is higher than that of

propane Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as ...

(657 kJ/mol) for each additional CH₂ unit. Compounds with unusually large strain energy include tetrahedranes, propellanes,

cubane-type cluster A cubane-type cluster is an arrangement of atoms in a molecular structure that forms a cube. In the idealized case, the eight vertices are symmetry equivalent and the species has Oh symmetry. Such a structure is illustrated by the hydrocarbon ...

fenestrane A fenestrane in organic chemistry is a type of chemical compound with a central quaternary carbon atom which serves as a common vertex for four fused carbocycles. They can be regarded as spiro compounds twice over. Because of their inherent st ...

s and cyclophanes.

References

{{reflist Chemical bonding Structural analysis