The Kelvin scale is preferred in scientific research because it's an absolute temperature scale. It begins at absolute zero, where particles theoretically have minimum motion and no thermal energy is emitted. This characteristic makes the Kelvin scale pivotal for calculations in thermodynamics and statistical mechanics, ensuring consistency and universality in scientific communication. Unlike the Celsius scale, which is based on the freezing and boiling points of water, the Kelvin scale provides a more fundamental and universal approach to measuring temperature, reducing ambiguities and inconsistencies that can arise from the relative nature of other temperature scales.

While the Kelvin scale is predominantly used in scientific contexts due to its absolute nature and direct relation to particle kinetic energy, it's not exclusively for scientific purposes. It can be used in any scenario where temperature measurement is required, including weather forecasting. However, the Celsius scale is often preferred in everyday contexts, including weather reporting, because it’s more intuitive for the general public, with easily identifiable reference points like the freezing and boiling points of water. The Kelvin scale, with its starting point at absolute zero, is less relatable for non-scientific everyday applications.

Absolute zero is theoretically the temperature at which particles have minimum thermal motion. Practically, it’s nearly impossible to reach due to the third law of thermodynamics, stating that the entropy of a perfect crystal approaches zero as the temperature approaches absolute zero. In the realm of quantum physics, reaching absolute zero would imply a system’s quantum ground state, where particles have the lowest allowed energy. This concept is foundational in quantum mechanics, underpinning phenomena like superconductivity and Bose-Einstein condensation, where particles behave in unusual, quantised ways that defy classical physics.

In principle, the average kinetic energy of particles increases with temperature. However, during phase changes, like melting or boiling, temperature can remain constant while energy is still absorbed or released by the substance. This energy facilitates the phase transition without increasing the kinetic energy of the particles. It's attributed to the potential energy changes as bonds between particles are broken or formed. Therefore, though generally temperature and kinetic energy are directly proportional, exceptions arise during phase changes where temperature remains constant amidst energy transfers.

The Kelvin scale doesn’t use the degree symbol because it’s an absolute scale, measuring the thermodynamic temperature. Each unit on the Kelvin scale is a Kelvin (K), not a degree Kelvin. This distinction underscores the fundamental difference between the Kelvin and Celsius scales. While the Celsius scale is a relative scale based on arbitrary points like the freezing and boiling points of water, the Kelvin scale begins at absolute zero, a fundamental limit of temperature. Dropping the degree symbol underscores the Kelvin scale's role in providing absolute, intrinsic temperature measurements, unanchored from specific material properties or phase transitions.