Understanding Heat, Temperature, and Thermodynamics

Venturi Tube and Thermodynamics

A Venturi tube is used to measure the velocity of liquids circulating inside a pressure pipe. It is also based on Bernoulli’s principle: when a liquid passes through this section, its pressure decreases, and its speed increases.

Thermodynamics is the part of physics that studies heat, and the difference between heat and temperature. Benjamin Thompson discovered that friction produces heat. Heat is the sum of all kinetic energy of the molecules. Temperature is a measure of the average kinetic energy of a body’s heated molecules. If a hot object and a cold object are in contact, over time, the hot object will cool and the cold object will heat up until they reach thermal equilibrium.

Temperature Scales

• Mercury Thermometers: A capillary tube with a bulb containing mercury. The mercury expands when heated and contracts when cooled. The temperature scale can range from -39°C to 357°C.
• Alcohol Thermometers: Can record temperatures lower than mercury thermometers, typically down to -130°C. Also uses Toluene.
• Fahrenheit Scale: Developed in 1714. The first thermometer used a scale where the lowest temperature achievable with a mixture of ice and ammonium chloride was 32°F, and the boiling point of water was 212°F.
• Celsius Scale: Created in 1742. This scale is based on the melting point of ice (0°C) and the boiling point of water (100°C) at a pressure of 760mm (1 atmosphere).
• Kelvin Scale: Based on absolute zero, the temperature at which the kinetic energy of molecules is zero. 0 K is equal to -273.15°C. There is no upper limit on the Kelvin scale.

Heat Capacity and Thermal Expansion

Heat capacity is defined as the ratio between the amount of heat supplied and the resulting temperature variation. Evidently, the higher the heat capacity of a substance, the more heat is required to raise its temperature.

Specific heat is defined as the heat capacity per unit mass. Changes in temperature affect body size; most materials expand when heated and contract when cooled. Gases expand more than solids.

• Linear Expansion: When a metal bar is heated, it undergoes growth in three dimensions. Linear expansion refers to the increase in length. The coefficient of linear expansion is the increase in length of a rod with an initial length of 1 meter when its temperature rises by 1°C.
• Area (Superficial) Expansion: When a surface expands, it increases its area. Area expansion is proportional to the initial area and the change in temperature.
• Cubical Expansion: Involves an increase in the dimensions of a body (length, width, and height), resulting in an increase in volume. The cubic expansion coefficient is the increase in volume experienced by an object with an initial volume of unity when its temperature increases by 1°C.
• Irregular Expansion of Water: While most substances expand when heated, some contract. Water exhibits irregular expansion.
• Expansion of Gases: Any gas subjected to a constant pressure will change its volume by approximately 1/273 of its volume at 0°C for every 1°C change in temperature.

Latent Heat

• Latent Heat of Fusion: When a substance melts or evaporates, it absorbs a certain amount of “latent” heat (meaning “hidden”).
• Sensible Heat: Sensible heat is the heat that, when supplied to a substance, raises its temperature.
• Latent Heat of Fusion (Detailed): The heat required for a change of physical state *without* a change in temperature. It is the amount of heat required to change 1 gram of a solid to 1 gram of liquid.
• Latent Heat of Vaporization/Condensation: When a liquid at a certain pressure is heated, it eventually boils. The heat of vaporization of a substance is the amount of heat required to change 1 gram of boiling liquid to 1 gram of steam, keeping the temperature constant.