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Facts about Temperature for Kids

  • Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot.
  • When a heat transfer path between them is open, heat spontaneously flows from bodies of a higher temperature to bodies of lower temperature.
  • The flow rate increases with the temperature difference, while no heat will be exchanged between bodies of the same temperature, which are then said to be in “thermal equilibrium”.
  • In thermodynamics, in a system of which the entropy is considered as an independent externally controlled variable, absolute, or thermodynamic, temperature is defined as the derivative of the internal energy with respect to the entropy.
  • They move according to Newton’s first law of motion, freely and independently of one another, except during collisions that last for negligibly short times.
  • The temperature of an ideal gas is proportional to the mean translational kinetic energy of its molecules.
  • Much of the world uses the Celsius scale (°C) for most temperature measurements.
  • If classical thermodynamic equilibrium conditions for matter are fulfilled to good approximation in each ‘cell’, then it is homogeneous and a temperature exists for it, and local thermodynamic equilibrium is said to prevail throughout the body.
  • Statistical mechanics provides a microscopic explanation of temperature, based on macroscopic systems’ being composed of many particles, such as molecules and ions of various species, the particles of a species being all alike.
  • Although very specialized laboratory equipment is required to directly detect the translational thermal motions, thermal collisions by atoms or molecules with small particles suspended in a fluid produces Brownian motion that can be seen with an ordinary microscope.
  • The thermal motions of atoms are very fast and temperatures close to absolute zero are required to directly observe them.
  • Molecules, such as oxygen (O2), have more degrees of freedom than single spherical atoms: they undergo rotational and vibrational motions as well as translations.
  • For experimental physics, hotness means that, when comparing any two given bodies in their respective separate thermodynamic equilibria, any two suitably given empirical thermometers with numerical scale readings will agree as to which is the hotter of the two given bodies, or that they have the same temperature.
  • While the zeroth law permits the definitions of many different empirical scales of temperature, the second law of thermodynamics selects the definition of a single preferred, absolute temperature, unique up to an arbitrary scale factor, whence called the thermodynamic temperature.
  • In most of the world (except for Belize, Myanmar, Liberia and the United States), the Celsius scale is used for most temperature measuring purposes.
  • On the empirical temperature scales, which are not referenced to absolute zero, a negative temperature is one below the zero-point of the scale used.
  • In the quantum mechanical description of electron and nuclear spin systems that have a limited number of possible states, and therefore a discrete upper limit of energy they can attain, it is possible to obtain a negative temperature, which is numerically indeed less than absolute zero.