Electron Volt to Foot-pound

Because subatomic energies in joules have absurdly small exponents — a visible-light photon carries about 3 × 10⁻¹⁹ J, but a convenient 1.9 eV. The electron volt is scaled to the quantum world, making numbers human-readable. It also doubles as a mass unit (via E = mc²): a proton is 938.3 MeV/c², far easier to work with than 1.673 × 10⁻²⁷ kg.

Visible light photons range from about 1.65 eV (deep red, 750 nm) to 3.1 eV (violet, 400 nm). Green light, where the human eye is most sensitive, sits around 2.3 eV. Ultraviolet photons start at 3.1 eV and can exceed 100 eV in the extreme UV. These energies are why UV can damage DNA (breaking molecular bonds of 3–5 eV) while visible light cannot.

A semiconductor's bandgap — the minimum energy to free an electron from its bond — is expressed in eV. Silicon has a bandgap of 1.12 eV, gallium arsenide 1.42 eV, and gallium nitride 3.4 eV. The bandgap determines which wavelengths of light a solar cell can absorb and what color an LED emits. Lower bandgap means longer-wavelength (redder) light.

The LHC accelerates protons to 6.5 TeV (6.5 × 10¹² eV) per beam, giving collisions a center-of-mass energy of 13 TeV. That sounds enormous, but 13 TeV is only about 2 microjoules — the kinetic energy of a flying mosquito. The power of the LHC lies in concentrating that energy into a space a million times smaller than an atom.

Multiply by 1.602 176 634 × 10⁻¹⁹. So 1 eV = 1.602 × 10⁻¹⁹ J, 1 keV = 1.602 × 10⁻¹⁶ J, and 1 MeV = 1.602 × 10⁻¹³ J. This conversion factor is exactly the elementary charge in coulombs, because an electron volt is defined as the energy gained by one electron charge crossing one volt of potential.

American automotive engineering adopted foot-pounds because it was the natural imperial torque unit — one pound-force at one foot from the crankshaft center. The convention became entrenched through SAE standards, shop manuals, and dyno testing. Converting to newton-meters (1 ft·lb ≈ 1.3558 N·m) is straightforward, but the entire US aftermarket ecosystem — torque wrenches, spec sheets, and mechanics' training — runs on foot-pounds.

Diesel engines compress air to much higher ratios (15–22:1 vs 8–12:1 for petrol), creating higher cylinder pressures that push harder on the piston — more force per stroke means more torque. But diesels rev lower (typically 4,000–4,500 RPM max vs 6,000–8,000 RPM) because the heavier rotating assembly and slower combustion limit speed. Since horsepower = torque × RPM / 5,252, the lower RPM ceiling caps peak horsepower despite the torque advantage.

Horsepower = torque (ft·lb) × RPM / 5,252. The constant 5,252 comes from unit conversion: 1 HP = 33,000 ft·lb/min, and 33,000 / (2π) ≈ 5,252. This means torque and horsepower curves on a dyno chart always intersect at exactly 5,252 RPM. Below that speed, torque is numerically higher; above it, horsepower is. This is why trucks optimize for low-RPM torque (pulling force) while sportscars chase high-RPM horsepower (speed).

Most passenger cars specify 80–100 ft·lb for wheel lug nuts; light trucks and SUVs call for 100–140 ft·lb; and heavy-duty trucks may require 450–500 ft·lb. Under-torquing risks the wheel coming loose, while over-torquing can warp brake rotors or snap studs. A calibrated torque wrench — not an impact gun alone — is the safe approach.

Muzzle energy in foot-pounds measures the kinetic energy of a bullet leaving the barrel. A 9 mm pistol produces about 350–400 ft·lb, a .45 ACP about 350–500 ft·lb, and a .308 rifle about 2,600–2,800 ft·lb. While muzzle energy is one factor in terminal performance, bullet construction, sectional density, and shot placement matter at least as much in real-world ballistics.