18.3 - A Lei Zero da Termodinâmica

Understanding Temperature and Thermometers

The Impact of Temperature on Matter

• Bodies undergo significant changes when heated or cooled, such as volume expansion in liquids and length increase in metal bars. Electrical resistance also increases with temperature variations.

• Early instruments for detecting temperature changes were called thermoscopes, developed by Galileo Galilei. These devices qualitatively assessed temperature without a defined scale.

• A thermoscope operates by placing a bulb in contact with a heated material, causing internal molecular motion to increase, which raises pressure and fluid levels within the device.

• When cooling occurs, kinetic energy decreases, leading to lower pressure and higher fluid levels in the bulb. This allows for inferring temperature changes based on fluid height.

• By comparing two fluids at different temperatures using the same bulb height, one can determine relative temperatures; if they are equal, both bodies are at thermal equilibrium.

Establishing Thermal Equilibrium

• The concept of thermal equilibrium states that if two bodies (A and B) are separately in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.

• This principle is crucial for defining what we call "temperature." If two bodies have the same temperature, they are considered to be in thermal equilibrium.

• Understanding this concept is essential as it lays the groundwork for further exploration into thermodynamics beyond just basic definitions.

Development of Thermometers

• The property of temperature becomes significant when discussing how bodies interact thermally; having the same temperature indicates an absence of heat flow between them.