Kilocalorie (th) to Inch-Ounce

Most foundational biochemical data — ATP hydrolysis (~7.3 kcal/mol), glucose oxidation (~686 kcal/mol), amino acid combustion values — were measured and published in kcal th before SI adoption. Rewriting decades of literature, lecture notes, and exam banks to kJ would introduce conversion errors and confusion. The field maintains kcal th by convention while acknowledging SI equivalents.

The standard free energy change (ΔG°) for ATP → ADP + Pi is approximately −7.3 kcal th/mol (−30.5 kJ/mol). Under actual cellular conditions, the value is closer to −12 to −14 kcal/mol because reactant and product concentrations differ from standard state. This energy drives muscle contraction, nerve impulses, protein synthesis, and virtually every energy-requiring process in living cells.

The classic Atwater factors (4 kcal/g carb, 4 kcal/g protein, 9 kcal/g fat) are averages from 19th-century bomb calorimetry, adjusted for digestibility. They can be off by 5–25% for specific foods. Almonds deliver ~20% fewer usable calories than labels claim because cell walls trap some fat from digestion. High-fiber foods also overcount. The FDA allows ±20% tolerance on label accuracy, so a "200 kcal" bar could legally contain 160–240 kcal.

Complete aerobic oxidation of one mole of glucose (C₆H₁₂O₆) releases approximately 686 kcal th (2,870 kJ). The human body captures about 38–40% of this in ATP; the rest dissipates as body heat. This is why exercise makes you warm — over half the food energy your muscles consume is released as thermal energy rather than mechanical work.

Fat molecules are highly reduced — their carbon atoms are bonded mostly to hydrogen, with very little oxygen. Oxidising them releases maximum energy because every C-H bond is converted to C=O and O-H bonds. Carbohydrates are already partially oxidised (they contain oxygen in their structure), so less additional oxidation is possible. Gram for gram, fat stores 2.25× more energy, which is why evolution favored fat as the body's long-term energy reserve — it packs the most kcal per gram of tissue weight.

RC servo motors are rated by torque in inch-ounces (or oz·in) because the forces involved are tiny. A standard micro servo produces 40–60 in·oz, which is enough to deflect a model aircraft aileron. High-torque digital servos for 1/10-scale RC cars reach 200–400 in·oz. The inch-ounce scale gives hobbyists whole-number specs that are easy to compare.

Servo motors produce more torque at higher voltage because the motor windings draw more current and generate a stronger magnetic field. A servo rated at 60 in·oz at 4.8 V might deliver 75 in·oz at 6 V — a 25% boost. RC pilots choose voltage based on the tradeoff: 6 V gives snappier response and more holding torque for aerobatics, but draws more current and generates more heat, reducing servo lifespan. Competition flyers often run 7.4 V for maximum performance, accepting shorter gear life.

Inch-ounces give convenient whole numbers for very small torques where newton-meters would be awkward decimals (e.g., 50 in·oz ≈ 0.353 N·m). The RC hobby, miniature clockwork, and precision instrument industries in the US developed around imperial units, and the convention persists even as SI gains ground. Many datasheets now list both units side by side.

A mechanical wristwatch mainspring delivers roughly 2–5 in·oz of torque. Larger mantel clocks may have mainspring torques of 10–30 in·oz. Escapement adjustments are even finer, sometimes below 1 in·oz. Horologists use inch-ounces (or gram-centimeters) because these scales match the delicate forces in timekeeping mechanisms.

A servo's inch-ounce rating tells you the maximum force it can exert at one inch from the output shaft. A 100 in·oz servo can hold 100 ounces (6.25 lb) at 1 inch, or 50 ounces at 2 inches. Robotics designers use this to size servos for joint loads — a small robotic arm lifting 1 lb at 4 inches needs at least 64 in·oz, plus a safety margin of 50% or more.