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Correlations in quantum fluids such as liquid ³He continue to be of high interest to scientists. Based on this prospect, the present work is devoted to study the effects of spin–spin correlation function on the thermodynamic properties of polarized liquid ³He such as pressure, velocity of sound, adiabatic index and adiabatic compressibility along different isentropic paths, using the Lennard–Jones potential and employing the variational approach based on cluster expansion of the energy functional. The inclusion of this correlation improves our previous calculations and leads to good agreements with experimental results.

In the present work, we have designed an electronic setup to experimentally verify that gravity does not directly affect the velocity of sound as stated by Lord Rayleigh. For this purpose, we have designed a setup comprising of two sensors namely ultrasonic sensor and accelerometer and a microcontroller Raspberry Pi to determine the values of sound velocity and acceleration due to gravity. The setup was then carefully enclosed in a box with bubble pack and dropped from a height of $\approx 12\mathrm{\text{meters}}$. At this height, there is no variation in air pressure and density, thus, the only parameter which is being varied is acceleration due to gravity. Under the free fall condition, the Raspberry Pi was programmed to control the working of both the sensors and store their responses in the memory card. The results show that the acceleration due to gravity acting upon the setup becomes negligible soon after it is dropped but the velocity of sound remains unaffected.