Notes on Thermodynamics Basics: Properties, Working Substances, and Units

Thermodynamics is the study of heat and work and those properties of substances that bear a relation to heat and work.

Surroundings: all matter and space outside a system.
Isolated system: a physical system that does not interact or exchange energy with its surroundings.
Control volume: the focused volume in space from which the substance flows.
Control surface: the surface that surrounds the control volume.
Phase: a quantity of matter having the same chemical composition or homogeneous.
Property: a quantity which serves to describe a substance.

Intensive Property: a property which does not depend on the mass of the substance, e.g. temperature, pressure, density, stress, velocity.
Extensive Property: a property which depends on the mass of the substance, e.g. volume, momentum, energy.

Working substance: a substance to which heat can be stored and from which heat can be extracted.

Pure Substance: a working substance whose chemical composition remains the same even if there is a change in phase (examples: Water, ammonia, Freon-12).
Ideal Gas: a working substance which remains in gaseous state during its operating cycle and whose equation of state is PV = mRT (examples: air, O2, CO2).

Newton's law (second law of motion): acceleration of a body is directly proportional to the resultant force acting on it and inversely proportional to its mass. The general form is F = ma where k is a proportionality constant.
In some unit systems, the equation is written as F = kma with k depending on the system of units.

CGS (centimeter-gram-second) system: 1 dyne force accelerates 1 gram mass at 1 cm/s^2.
MKS (meter-kilogram-second) system: 1 newton force accelerates 1 kilogram mass at 1 m/s^2.
FPS (foot-pound-second) system: 1 lbf accelerates 1 slug mass at 1 ft/s^2.

CGS system: 1 gforce accelerates a 1 gmass at 980.66 cm/s^2 (text shows this relation; note the numeric 980.66 comes from gravity in cm/s^2).
CGS system: 19 force accelerates a 19 mass at 980.66 cm/s^2 (text shows a second example with a scaling factor; k = 98066 & m·cm in the garbled slide).
MKS system: 1 kg force accelerates a 1 kg mass at 9.8066 m/s^2; this illustrates that in some presentations k ≈ 9.8066 for converting kgf to N.
MKS system: k = 9.8066 (illustrative value shown in slides).
FPS system: 1 lb force accelerates a 1 lb mass at 32.174 ft/s^2; in this system k = 32.174 (illustrative value shown in slides).
FPS system: k = 32.174 (another line showing the same value).

In a system where a unit force produces unit acceleration on a body with unit mass:
F is force in pounds, m is mass in pounds, a is acceleration in ft/s^2.
1 poundal = 1 lbm ft/s^2
In another statement:
1 pound = 1 slug ft/s^2 (the slide uses this to relate pounds-force to slug-based dynamics).

Mass: a property of matter that constitutes one of the fundamental physical measurements or the amount of matter a body contains.
Units: lbm, slugs, kgm, or kg.
Weight: the force acting on a body in a gravitational field, equal to the product of its mass and the gravitational acceleration of the field.
Units: lbf, kgf, N, or kN.

Example 1: What is the weight of a 66-kgm man at standard condition?
Example 2: The weight of an object is 50 lb. What is its mass at standard condition?
Example 3: What is the mass in grams and the weight in dynes and in gram-force of 12 oz of salt? Local g is 9.65 m/s^2; (1 lbm = 16 oz).
Assignment #1:
Five masses in a region where the acceleration due to gravity is 30.5 ft/s^2 are as follows:
m1 is 500 g of mass;
m2 weighs 800 gf;
m3 weighs 15 poundals;
m4 weighs 3 lbf;
m5 is 0.10 slug of mass.
What is the total mass expressed (a) in grams (b) in pounds (c) in slugs.

The slides introduce a variety of unit systems and show how Newton's law is expressed differently depending on whether k = 1 and whether the units are taken in CGS, MKS, or FPS.
The concept of mass vs. weight is emphasized, along with the idea that weight is not intrinsic to an object but depends on the local gravitational field.
The material includes a practical exercise set (Assignment #1) to convert and relate mass and weight across unit systems given a local gravitational acceleration.
The notational differences (lbm vs slug vs kgm, lbf vs kgf vs N) are highlighted, underscoring the importance of unit consistency in thermodynamics calculations.