This section focuses on the nature of heat, measuring temperature, the consequences of changes in temperature and the methods of transfer of heat energy.
What is heat energy?
Heat energy is energy which is transferred because of temperature differences between objects. As with any other form of energy, the SI unit is the Joule(J).
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There have been two noteworthy theories on the nature of heat.
Caloric Theory of Heat
This is the theory in thermodynamics which dictates that objects with different temperatures have differing densities of an invisible, weightless fluid called ‘caloric’. This theory was replaced by the kinetic theory of heat.
Kinetic Theory of Heat
This posits that matter is made up of tiny particles which are constantly in motion. The heat a body possesses is due to the kinetic energy that the body’s particles have. The following assumptions are made:
- A macroscopic volume consists of a large number of small particles
- No intermolecular forces are present between particles except for when there are collisions
- There is large separation between particles
- Particles have random velocities
- Collisions between particles are elastic (total kinetic energy is always conserved)
Contribution of James Prescott Joule
Joule conducted a paddle-wheel experiment which supported the principle of conservation of energy and showed an approximation for the mechanical equivalent of heat (how much motion produces a certain amount of heat).
Simulation on the mechanical equivalent of heat: Physics Aviary Mechanical Equivalent of Heat Lab