Forensic Physics
A complete, journal-grade reference for the forensic-physics student and the working trace-evidence + imaging analyst: light and the forensic electromagnetic spectrum (alternate-light sources + light-matter interaction), the full microscopy stack (stereo + comparison + polarising + fluorescence + SEM/TEM + EDS), forensic photography and specialised UV/IR/ALS/digital imaging, density and refractive index and polarimetry, glass + soil + paint trace-evidence physics, building materials and tool marks and impression evidence, restoration of erased serial numbers + vehicle examination + accident-reconstruction physics, and the emerging frontier of forensic acoustics, forensic engineering and terahertz + hyperspectral + quantum + AI-assisted imaging.
- 99hours
- 33topics
- 10modules
Light, photons and the forensic spectrum
The physics of light as it lands in a forensic laboratory: the electromagnetic spectrum from gamma through radio with the photon model, the forensic-laboratory light sources (tungsten-halogen, mercury vapour, xenon arc, monochromatic lasers, Polilight + Crime-lite alternate-light sources), and the light-matter interactions that drive every optical examination (absorption, transmission, reflection, scattering, fluorescence, phosphorescence).
Start module- Light, Photons and the Forensic EM SpectrumThe electromagnetic spectrum from gamma to radio as the forensic analyst meets it: the dual wave + particle nature of light, the Planck-Einstein photon model and E = hν, wavelength + frequency + energy relationships, the spectrum bands that matter on a forensic bench (gamma, X-ray, UV-C/B/A, visible, near-IR + mid-IR + far-IR, microwave, radio) and the canonical applications of each band (X-ray imaging for concealed evidence, UV for biological-fluid screening, visible for documentation, IR for ink and bloodstain).13 min
- Forensic Light Sources and Alternate Light ExaminationThe forensic-laboratory light sources and how the analyst picks one: tungsten-halogen (continuous broadband), mercury vapour and xenon arc (high-intensity UV + visible), monochromatic lasers (argon-ion 488 nm, Nd:YAG 532 nm) and the modern alternate-light source platforms (Foster + Freeman Crime-lite, Rofin Polilight, Spex Mini-Crimescope) with their bandpass filters; the wavelength-selection logic for biological fluids, fingerprint enhancement, fibre + paint examination, document inks and bruise visualisation.13 min
- Light-Matter Interaction: Absorption, Reflection, FluorescenceThe physics that explains why a forensic analyst sees what they see: absorption (Beer-Lambert law, chromophore + auxochrome, why bloodstains appear dark at 415 nm), transmission and reflection (specular vs diffuse, the Kubelka-Munk model on paper), scattering (Rayleigh vs Mie vs Raman, why white powders look white), and fluorescence + phosphorescence (Stokes shift, Jablonski diagram, fluorescence lifetime, the practical separation of fluorescent vs reflective evidence on ALS).13 min
Forensic microscopy
The microscopy stack that anchors trace-evidence and biological-fluid examination: optical fundamentals (magnification, resolution, numerical aperture, Koehler illumination, parfocality), the stereo and comparison microscopes used at every bench, polarising and fluorescence microscopes for anisotropic and labelled samples, and the electron microscopy (SEM, TEM, EDS) that delivers GSR particle confirmation and paint-layer elemental mapping.
Start module- Microscopy Fundamentals: Magnification, Resolution and NAThe optics every microscopist must own: magnification vs resolution (Rayleigh and Abbe criteria), numerical aperture (NA) and immersion-medium choice, depth of field and parfocality, Koehler vs critical illumination, the eyepiece + objective lens chain and infinity-corrected vs finite-tube-length systems; the standard ISO 8576 + ASTM E766 magnification-calibration workflow that supports court-admissible measurement.13 min
- Stereo Microscope and Comparison MicroscopeThe two workhorse forensic microscopes: the stereo (low-magnification, 3D, real-image-pair) for initial sample triage, fibre and hair examination, document inspection and trace-evidence sorting; the comparison microscope (cross-mounted dual stage with optical bridge) for side-by-side tool-mark, bullet, cartridge-case and hair-fibre comparison — the instrument that anchors the AFTE comparison frame and the PCAST 2016 critique of subjective firearm/toolmark identification.13 min
- Polarising and Fluorescence MicroscopesTwo specialised optical platforms: the polarising microscope (polariser + analyser at crossed Nicols, retardation plate, the anisotropic-material identification frame for fibres, minerals, drug crystals, asbestos via the McCrone 1980 protocol) and the fluorescence microscope (epi-illumination, dichroic mirror + excitation + emission filter cube, the standard DAPI + FITC + TRITC + Cy5 channels, applications in biological-fluid identification and sperm-head visualisation under DFSS + SOFT protocols).13 min
- Electron Microscopy: SEM, TEM and EDSElectron microscopy in the forensic laboratory: scanning electron microscope (SEM with secondary and back-scattered electron detectors, the topographic vs Z-contrast contrast frame) for gunshot-residue particle confirmation (the ASTM E1588 Pb-Sb-Ba criterion) and paint cross-section topography; transmission electron microscope (TEM) for ultrastructure of fibres and pigments; energy-dispersive X-ray spectroscopy (EDS) for elemental analysis; SEM-EDS as the gold-standard GSR confirmation reference across FBI, ENFSI and SWGGUN.14 min
Forensic photography and imaging
How a forensic photograph becomes courtroom evidence: photography fundamentals (sensors, lenses, exposure, depth of field, perspective control, ring-flash and oblique lighting), the crime-scene workflow (overall + mid-range + close-up + scale + chain of custody), specialised imaging (UV-reflectance, IR-reflectance + transmittance, ALS-assisted, laser-induced fluorescence, infrared luminescence), and digital evidence integrity (RAW vs JPEG, EXIF metadata, hashing, the Daubert + Frye + BSA 2023 § 65B admissibility frames).
Start module- Forensic Photography: FundamentalsThe camera and the exposure triangle as the forensic photographer manipulates them: image sensor (CCD vs CMOS, full-frame vs APS-C, dynamic range), lens classes (wide-angle vs macro vs tilt-shift, focal length and perspective), aperture (f-stop, depth of field, diffraction limit), shutter speed (motion freeze, long exposure, flash sync), ISO and noise, white balance and colour temperature; the rule-of-thirds + leading-lines composition frame plus the chain-of-custody documentation overlay.13 min
- Crime-Scene Photography WorkflowThe four-tier scene-photography protocol (overall, mid-range, close-up, comparison) practised by every CSI: the establishing wide-angle shots for context, the mid-range relationship shots that bind evidence to a scene reference, the close-ups with scale + colour reference (ABFO No. 2 + Kodak Grey Card + L-scale), the comparison frame with a known-vs-questioned arrangement; bracketing and panorama stitching for low-light or large scenes; the SWGIT + IAI + ENFSI photography standards and the photo log that ties every frame to the chain of custody.13 min
- Specialised Imaging: UV, IR, Laser and ALSThe wavelength-selective imaging classes that pull invisible evidence into the visible: UV-reflectance (gunshot-residue, bite-mark documentation, latent bruising via the Vogeley 2002 protocol), UV-fluorescence (biological-fluid screening), IR-reflectance and IR-transmittance (obliterated ink, layered documents, gunshot soot through bloodstain), laser-induced fluorescence (fingerprints on porous and difficult substrates), and infrared luminescence (sequence-of-ink-strokes in document examination).14 min
- Digital Imaging Evidence and Court AdmissibilityThe integrity chain that keeps a forensic photograph admissible: RAW vs JPEG vs TIFF capture choice, EXIF metadata as provenance, write-once media + hash-based integrity (MD5 + SHA-256 + SHA-3) under the SWGDE digital-evidence standards, image enhancement permitted vs prohibited (the FBI + SWGIT + ENFSI guidelines), and the courtroom admissibility frames — US Daubert v. Merrell Dow 1993 and Federal Rules of Evidence 901 + 1002, UK Police and Criminal Evidence Act 1984 + R v. Tobi, India's BSA 2023 § 63 (electronic record) and § 65B certificate (replacing IEA § 65B).14 min
Density, refractive index and polarimetry
The three physical measurements that drive trace-evidence comparison: density (sink-float, density-gradient column, pycnometry, hydrostatic weighing), refractive index (Becke-line, GRIM-3 hot-stage automated phase-contrast, immersion-oil method, the Locke 1985 forensic protocol), and polarimetry (optical rotation, sucrose and drug analysis, the saccharimeter and Laurent polarimeter).
Start module- Density Measurement: Forensic MethodsDensity as a forensic comparison parameter: physical basis (mass per unit volume, temperature dependence), measurement classes — sink-float (qualitative match-or-mismatch using bromoform + bromobenzene mixtures), density-gradient column (continuous liquid column with neutral-buoyancy zone), pycnometry (precise volumetric flask), hydrostatic weighing and modern oscillating-U-tube digital densitometers; the casework arc for soil, glass and polymer comparison and the role of the Stokes settling formula in density-gradient analysis.13 min
- Refractive Index: Becke Line, GRIM and Mettler Hot StageThe single most discriminating physical property of glass and many minerals: theory of refractive index (Snell's law, Cauchy + Sellmeier dispersion), measurement methods — Becke-line (immersion-oil match-or-mismatch under the polarising microscope), GRIM-3 (Glass Refractive Index Measurement, the Foster + Freeman automated phase-contrast platform), Mettler FP-90 hot-stage temperature-variation method, oil-Becke calibration with the standard Locke 1985 protocol; the ENFSI ENG3-2013 glass-comparison guideline and the ASTM E1967 standard.13 min
- Polarimetry and Optical Rotation in Forensic AnalysisThe physics of optical rotation as a forensic discriminator: chirality and enantiomers, plane-polarised light and the polariser-analyser pair, specific optical rotation [α] and the Biot equation, the half-shade and Laurent polarimeters; forensic applications in sucrose / lactose adulteration (the FSSAI 2011 + Codex CXS 212 standards), illicit-drug enantiomer differentiation (D-vs-L-methamphetamine, the DEA enantiomer-rule frame), essential-oil authenticity and pharmaceutical-counterfeiting casework.13 min
Glass evidence
The forensic physics of glass from cradle to courtroom: glass types and manufacture (soda-lime float, borosilicate, tempered, laminated, bullet-resistant, automotive windshield + side glass), fracture analysis (radial vs concentric cracks, Wallner lines, conchoidal hackle, direction-of-force + sequence-of-impact reconstruction, the R v. Hoey 2007 glass-fragment debate), and comparison casework (RI matching via GRIM, density gradient, LA-ICP-MS elemental fingerprinting via the ASTM E2927 standard).
Start module- Glass: Types, Properties and ManufactureThe glass classes a forensic analyst must distinguish: soda-lime float glass (Pilkington 1959 process, the dominant container + window class), borosilicate (Pyrex, low expansion, laboratory + cookware), tempered safety glass (heat-treated, granular crumble pattern), laminated automotive windshield (PVB interlayer), bullet-resistant multi-layered + polycarbonate composites, optical and lead crystal; the chemical composition (SiO2 + Na2O + CaO + Al2O3 + MgO + B2O3 + K2O + PbO) and the elemental + RI + density signatures each class leaves for forensic discrimination.13 min
- Glass Fragmentation and Direction-of-Force AnalysisHow a forensic analyst reads sequence and direction off a glass fracture: the radial + concentric crack pattern, Wallner lines (the rib markings that record fracture front velocity) and the 3R rule (Radial cracks form Right-angle to the Reverse side under stress), conchoidal hackle marks; direction-of-force reconstruction from cone fractures and shell chips; sequence-of-impact analysis from intersecting fractures; high-velocity impact (bullet) vs low-velocity impact (hammer) differentiation; the R v. Hoey 2007 Northern Ireland glass-fragment evidence debate.14 min
- Glass Comparison: RI, Density and LA-ICP-MSThe casework workflow for source-attribution of glass fragments: physical features (colour, thickness, fluorescence), RI matching via GRIM-3 under the ENFSI ENG3-2013 guideline, density via density-gradient column, elemental fingerprinting via LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) under the ASTM E2927 standard and the multivariate-statistics match criteria (Hotelling's T2, Mahalanobis distance); the casework anchors from FBI + RCMP + ENFSI laboratories and the Bayesian likelihood-ratio reporting frame.14 min
Soil and earth evidence
Soil as a forensic trace-evidence class: composition and classification (mineral fraction, organic fraction, water + air content, USDA texture triangle, the Munsell colour system), examination techniques (density-gradient separation, particle-size distribution, mineralogy via polarising microscopy and XRD, forensic palynology, forensic diatomology), and comparison casework with statistical inference (the Murray-Tedrow framework, the FBI Soil Examination Unit protocols, the ENFSI European geological evidence guideline).
Start module- Soil Composition, Classification and the Munsell SystemSoil as a heterogeneous trace-evidence class: physical composition (mineral fraction, organic fraction, soil water, soil air, soil organisms), the USDA + ISSS particle-size triangle (sand + silt + clay) and the texture classes, soil classification systems (USDA Soil Taxonomy, World Reference Base for Soil Resources WRB, FAO Soil Map of the World, Indian Soil Survey), and colour standardisation via the Munsell Soil Colour Chart (hue + value + chroma) under the ASTM D1535 frame.13 min
- Soil Examination: Density Gradient, Mineralogy and PalynologyThe forensic-soil examination stack: density-gradient column with bromoform + bromobenzene to produce a particle-fraction profile; particle-size distribution by sieving + laser-diffraction; mineralogy via polarising microscopy + powder XRD (X-Ray Diffraction) for the quartz + feldspar + clay-mineral pattern; forensic palynology (the Bryant + Mildenhall pollen + spore casework frame, used in the Mihaela Marincu 2009 Bosnia mass-grave investigations); forensic diatomology for drowning attribution and soil-source linkage.14 min
- Soil Comparison Casework and Statistical InferenceHow a forensic-soil scientist closes the loop: questioned vs known + control-sample design, the Murray + Tedrow 1992 + 2017 forensic-geology comparison frame, the FBI Soil Examination Unit comparison protocols, the ENFSI ENG-FG1 European geological evidence guideline; statistical inference with multivariate methods (PCA, Mahalanobis distance, soil-mineral ratio fingerprinting); courtroom casework anchors — the John Norman Collins 1969 Michigan case, the Lindbergh-baby 1932 soil-evidence template, and the Ujjain 2013 Bharat Bandh casework in Indian jurisprudence.13 min
Paint, pigment and coating evidence
Paint as the highest-volume trace-evidence class after fibres: composition (binder + pigment + extender + additive + solvent), paint types (automotive OEM + refinish, architectural latex + alkyd, industrial epoxy + polyurethane, art-and-restoration pigments), layer examination (microtome cross-section, comparison microscopy, FTIR microspectroscopy, pyrolysis GC-MS), and the comparison databases (RCMP Paint Data Query PDQ, ENFSI European Collection of Automotive Paints EUCAP) that drive automotive hit-and-run casework.
Start module- Paint Composition, Types and Binder ChemistryPaint as a four-component system: binder (alkyd, acrylic, epoxy, polyurethane, nitrocellulose), pigment (TiO2, iron oxide, phthalocyanine, carbon black), extender + filler (CaCO3, kaolin, talc, barium sulphate), solvent + additive (driers, plasticisers, UV stabilisers); paint classes by application — automotive OEM (the basecoat + clearcoat over electrocoat + primer four-layer system) vs automotive refinish, architectural latex + alkyd, industrial epoxy + polyurethane, art-and-restoration pigments; the comparison-relevant layer-by-layer architecture.13 min
- Paint Layer Examination: Cross-Section, FTIR and Py-GC-MSThe forensic-paint examination workflow: microtome cross-section preparation, comparison microscopy under stereo + polarising + fluorescence for layer count + thickness + colour sequence; chemical identification via FTIR microspectroscopy (binder + pigment functional-group assignment via the IRUG + Bell-Labs + Bio-Rad reference libraries), Raman microspectroscopy (pigment + extender identification), pyrolysis GC-MS (Py-GC-MS, polymer-class identification via the ASTM E2937 standard), SEM-EDS for elemental layer mapping.14 min
- Paint Databases (PDQ, EUCAP) and Comparison CaseworkThe comparison-database infrastructure for automotive-paint hit-and-run casework: the RCMP Paint Data Query (PDQ, > 75,000 automotive paint formulations from major OEMs since 1976), the European Collection of Automotive Paints (EUCAP) at the Bundeskriminalamt Wiesbaden; the SWGMAT + ENFSI EPG paint-comparison protocols (microscopical + spectroscopic + Bayesian reporting frame); courtroom casework anchors from the Christopher Coleman 2009 US case, the UK R v. Adams 1996 paint-evidence judgment, and the routine Indian hit-and-run investigations under the Motor Vehicles Act 1988 and BNS 2023 § 106.13 min
Building materials, tool marks and impression evidence
The patterned-evidence and material-class topics that close the trace-physics arc: cement + plaster + brick + mortar examination (composition, comparison via XRD + FTIR), tool-mark fundamentals (the AFTE class + subclass + individual frame, striated vs impressed marks, mechanics of mark formation), tool-mark comparison (comparison microscopy, IBIS-class 3D imaging, the PCAST 2016 challenge to subjective comparison), and impression evidence (footprints, tyre marks, the SWGTREAD standard, casting with Dental Stone + ESLA electrostatic dust-print lift).
Start module- Cement, Plaster and Building-Material EvidenceThe building-material trace class: cement composition (Portland cement, the C3S + C2S + C3A + C4AF clinker phases under the ASTM C150 + IS 269 standards), plaster (gypsum + lime + calcium sulphate hemihydrate), mortar + concrete + brick + glass-wool insulation; comparison methods (XRD for crystalline-phase identification, FTIR for sulphate + carbonate + silicate functional groups, SEM-EDS for elemental fingerprinting); forensic casework — wall-breach reconstruction, hit-and-run with building-material transfer, the 9/11 dust-fingerprint analysis as a casework reference.12 min
- Tool Marks: Fundamentals, Striations and ImpressionsThe tool-mark evidence class: tool taxonomy (cutting, shearing, gripping, prying, drilling), the mechanics of mark formation (force + angle + relative motion), striated marks (parallel scratches from sliding-edge tools — screwdriver, knife, file) vs impressed marks (compressed surface impressions from non-sliding tools — hammer, bolt-cutter); the AFTE class + subclass + individual characteristics frame, mark-vs-tool correspondence, and the PCAST 2016 Report critique of subjective tool-mark identification.13 min
- Tool-Mark Comparison Microscopy and 3D ImagingThe comparison-stage workflow: side-by-side comparison microscopy with the cross-mounted dual stage and optical bridge; modern 3D imaging platforms (Cadre TopMatch, NIST IBIS-class systems, Foster + Freeman Evofinder for toolmark + cartridge-case + bullet acquisition); the Congruent Matching Cells (CMC) and Algorithmic Comparison Score frameworks; the AFTE Theory of Identification 1992 + 2011 standard and the courtroom debate post-PCAST 2016 + 2024 OSAC update.13 min
- Impression Evidence: Footprints, Tyre Marks and CastingThe two-dimensional and three-dimensional impression evidence classes: footwear impressions (the SWGTREAD outsole-comparison frame, the FBI footwear-database, the RCMP Treadmate database) with class + subclass + individual features (wear pattern, randomly-acquired characteristics); tyre impressions (tread design, tyre-print individualisation, the Tracking Evidence database); casting methods — Dental Stone for soil + sand prints, sulphur for snow prints, electrostatic dust-print lifter (ESLA) for indoor dust prints; the Tetreault Hill v. R 2018 Canadian footwear-evidence judgment.13 min
Restoration of erased marks, vehicle and accident physics
Three high-value applied-physics topics: restoration of obliterated serial numbers (chemical etching via Fry's reagent + Davis reagent, magnetic-particle method, electrolytic, ultrasonic cavitation, scanning electron + neutron-induced X-ray fluorescence), vehicle examination (paint cross-section, headlight + side-marker bulb hot-vs-cold filament analysis, tyre-print individualisation, the Daubert-grade vehicle-component database), and accident-reconstruction physics (velocity from skid marks, momentum conservation in two-vehicle collisions, the SAE J1739 + IRTE reconstruction frameworks, biomechanics of pedestrian impact).
Start module- Restoration of Erased Serial NumbersThe applied-physics workflow for recovering obliterated serial numbers on firearms, engine blocks and other metallic objects: the underlying mechanism (cold-working stress field under the stamped digit persists in the metal lattice even after the surface is filed or ground); chemical etching methods — Fry's reagent on steel (HCl + CuCl2 + H2O), Davis reagent on aluminium (HCl + CuCl2), Turner's reagent on copper alloys; physical methods — magnetic-particle inspection (only for ferromagnetic metals), ultrasonic cavitation, electrolytic etching; advanced — scanning electron microscopy and neutron-induced X-ray fluorescence at synchrotron beamlines.13 min
- Vehicle Examination: Paint, Glass, Tyre, Headlight FilamentThe vehicle-component examination stack in hit-and-run + accident casework: paint transfer (cross-section + FTIR + PDQ match), broken-glass + headlight-lens fragment matching (RI + LA-ICP-MS, the ASTM E2927 frame), tyre-impression individualisation, headlight + side-marker bulb hot-vs-cold filament analysis (a hot filament tungsten stretches and oxidises on impact; a cold filament fractures cleanly — the practical test for headlights-on-vs-off at the moment of collision), windshield-fragmentation reconstruction; the Indian Motor Vehicles Act 1988 + BNS § 106 casework frame.13 min
- Accident Reconstruction Physics: Velocity, Momentum and Skid MarksThe physics that supports a courtroom accident-reconstruction opinion: velocity estimation from skid-mark length (the v = sqrt(2 μ g d) friction-coefficient formula), momentum conservation in two-vehicle collisions (elastic vs inelastic, the impulse-momentum theorem and crush-zone energy absorption), centripetal force and yaw-mark analysis, pedestrian-impact biomechanics (the head-throw distance + body-launch model from Searle 1993); the SAE J1739 + IRTE + ENFSI Road Transport reconstruction frameworks and the courtroom Daubert + Frye challenges to reconstruction opinions.14 min
Forensic acoustics, engineering and emerging physics
The frontier of forensic physics: acoustics (gunshot acoustic analysis with muzzle blast + shock-wave separation, environmental-recording authentication, the ENF electrical-network-frequency timestamping), forensic engineering (materials testing, fractography, fatigue + creep failure analysis, the NIST-NCSTAR WTC reports as casework templates), and emerging physics (terahertz imaging for concealed-weapon and ink-layer detection, hyperspectral imaging for documents + bloodstain ageing, quantum sensing pilots, AI-assisted image and pattern analysis with the ENFSI 2023 AI position paper).
Start module- Forensic Acoustics and Gunshot Acoustic AnalysisAcoustic evidence in forensic casework: sound-wave physics (frequency + amplitude + propagation + reflection + Doppler), the forensic-recording examination workflow under the SWGDE + ENFSI Forensic Speech and Audio guidelines; gunshot acoustic analysis — separation of the muzzle blast (subsonic spherical wave) from the supersonic bullet shock wave (Mach cone) for distance-to-shooter localisation, the JFK Warren Commission + HSCA acoustic-evidence debate, modern ShotSpotter + SST gunshot-locator systems; the ENF (Electrical Network Frequency) timestamping for recording-authenticity validation.13 min
- Forensic Engineering: Failure Analysis and FractographyThe engineering-physics overlap with forensic casework: materials testing (tensile + compressive + fatigue + creep + impact + hardness), fractography (the fracture-surface morphology that records loading history — brittle cleavage, ductile dimples, fatigue striations, beach marks, river patterns), failure-mode classification under the ASM Handbook frame; landmark casework — the de Havilland Comet 1954 metal-fatigue investigation, the NIST-NCSTAR World Trade Center reports, the Bhopal 1984 chemical-release engineering analysis, the Boeing 737 MAX 2018 + 2019 MCAS failure analysis.13 min
- Emerging Physics: Terahertz, Hyperspectral, Quantum and AI ImagingThe frontier of forensic physics: terahertz (THz) imaging for concealed-weapon detection, layered-document inspection and pharmaceutical-counterfeit screening (the 0.1 to 10 THz band that penetrates clothing and plastic but is non-ionising); hyperspectral imaging for bloodstain ageing, ink-stroke sequencing and document examination (the Foster + Freeman VSC8000 + FORAY platform); quantum-sensing pilots in NMR + magnetometry; AI-assisted image and pattern analysis (CNN-based footwear and fingerprint matching, the ENFSI 2023 AI position paper and the US OSAC + NIST validation requirements).14 min