The Poynting effect may refer to two unrelated physical phenomena. Neither should be confused with the

Poynting–Robertson effect The Poynting–Robertson effect, also known as Poynting–Robertson drag, named after John Henry Poynting and Howard P. Robertson, is a process by which solar radiation causes a dust grain orbiting a star to lose angular momentum relative to its o ...

. All of these effects are named after

John Henry Poynting John Henry Poynting FRS (9 September 185230 March 1914) was an English physicist. He was the first professor of physics at Mason Science College from 1880 to 1900, and then the successor institution, the University of Birmingham until his deat ...

, an English physicist.

Solid mechanics

In solid mechanics, the Poynting effect is a

Finite strain theory In continuum mechanics, the finite strain theory—also called large strain theory, or large deformation theory—deals with deformations in which strains and/or rotations are large enough to invalidate assumptions inherent in infinitesimal strai ...

effect observed when an elastic cube is sheared between two plates and stress is developed in the direction normal to the sheared faces, or when a cylinder is subjected to torsion and the axial length changes. The Poynting phenomenon in torsion was noticed experimentally by J. H. Poynting.

Chemistry and thermodynamics

In thermodynamics, the Poynting effect generally refers to the change in the

fugacity In chemical thermodynamics, the fugacity of a real gas is an effective partial pressure which replaces the mechanical partial pressure in an accurate computation of the chemical equilibrium constant. It is equal to the pressure of an ideal gas whic ...

of a liquid when a non-condensable gas is mixed with the vapor at saturated conditions. :

\ln \frac  = \frac \int_^ v_\text \, dp

Equivalently in terms of vapor pressure, if one assumes that the vapor and the non-condensable gas behave as ideal gases and an ideal mixture, it can be shown that:Wark, Kenneth ''Advanced Thermodynamics for Engineers''. New York: McGraw-Hill, 1995 :

\ln \frac  = \frac ( P - p_ ) \!

where :

p_v

is the modified vapor pressure :

p_

is the unmodified vapor pressure :

v_

is the liquid molar volume :

R

is the liquid/vapor's gas constant :

T

is the temperature :

P

is the total pressure (vapor pressure + non-condensable gas) A common example is the production of the medicine

Entonox Nitrous oxide, is an inhaled gas used as a pain medication and together with other medications for anesthesia. Common uses include during childbirth, following trauma, and as part of end-of-life care. Onset of effect is typically within half a m ...

, a high-pressure mixture of

nitrous oxide Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

. The ability to combine and at high

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

while remaining in the gaseous form is due to the Poynting effect.

References

* C.O. Horgan and J. G. Murphy, ''Poynting and reverse Poynting effects in soft materials'', Soft Matter, 13, 2017, 4916-4923. Elasticity (physics) Rubber properties Gases {{physics-stub