Glossary of Key Terms¶
Definitions of the recurring physical concepts used across the 18 experiments and 6 workshops in this guide, in alphabetical order. Each entry links back to the experiment(s) where the term is most central.
A¶
Adiabatic compressibility (β) — The fractional decrease in volume per unit increase in pressure of a medium under conditions of no heat exchange; related to the velocity of sound by β = 1/(ρv²). See Ultrasonic Interferometer.
Angle of twist (θ) — The angle through which one end of a wire rotates relative to the other under an applied torque; proportional to the applied couple for an elastic wire. See Static Torsion.
B¶
Ballistic pendulum — A device that determines a projectile's speed by catching it in a swinging pendulum block, combining momentum conservation (during the catch) with energy conservation (during the swing). See Ballistic Pendulum.
Beat period (T_beat) — The period over which oscillatory energy visibly transfers back and forth between two weakly coupled oscillators with slightly different normal-mode frequencies. See Coupled Pendulums.
Bulk modulus (K) — A measure of a substance's resistance to uniform compression, K = ρv² for a fluid, where v is the speed of sound in it. See Ultrasonic Interferometer.
C¶
Conjugate points — A pair of pivot points on either side of the centre of gravity of a compound pendulum that give the same period of oscillation; the basis of Kater's reversible pendulum. See Compound (Bar) Pendulum.
D¶
Damping ratio (ζ) — A dimensionless measure of how strongly oscillations in a system are damped, relative to the critical damping value that just prevents oscillation altogether. See Damped Oscillations, Automotive Shock-Absorber Damping Design.
E¶
Elastic limit — The maximum stress a material can withstand while still returning completely to its original shape once the load is removed; beyond it, permanent (plastic) deformation occurs. See Non-Uniform (Cantilever) Bending, Structural Beam Load Testing.
F¶
Frictional couple (τ_f) — The torque exerted by friction at a rotating axle's bearings, opposing its rotation and dissipating its kinetic energy over time. See Flywheel.
L¶
Logarithmic decrement (δ) — The natural logarithm of the ratio of two successive peak amplitudes in a damped oscillation, δ = ln(A_n/A_{n+1}); a direct, dimensionless measure of the damping strength. See Damped Oscillations.
M¶
Maximum permissible error — The upper bound on the uncertainty in a calculated result, obtained by propagating the least-count (instrument resolution) errors of the individually measured quantities through the governing formula.
Moment of inertia (I) — The rotational analogue of mass: a measure of a body's resistance to angular acceleration about a given axis, depending on both its mass and how that mass is distributed relative to the axis. See Bifilar Suspension, Torsional Pendulum, Flywheel.
N¶
Normal mode — A pattern of motion in a coupled oscillating system in which every part of the system oscillates at the same single frequency; any general motion of the system can be written as a superposition of its normal modes. See Coupled Pendulums.
P¶
Poiseuille's law — The relation giving the volume flow rate of a liquid through a narrow tube under laminar flow, proportional to the fourth power of the tube's radius. See Poiseuille's Method.
Precession — The slow, steady sweeping motion of a spinning body's rotation axis around another axis, caused by an applied torque that is perpendicular to its spin angular momentum. See Gyroscopic Precession.
Q¶
Quality factor (Q) — A dimensionless measure of how lightly damped an oscillator is; equivalently, the sharpness of its resonance peak, Q = f₀/Δf, or approximately π/δ from the decay of a free oscillation. See Damped Oscillations, Forced Oscillations & Resonance.
R¶
Radius of gyration (k) — The distance from an axis at which the entire mass of a body could be concentrated to give the same moment of inertia about that axis. See Compound (Bar) Pendulum.
Resonance — The dramatic increase in the steady-state amplitude of a driven oscillator when the driving frequency approaches its natural frequency. See Forced Oscillations & Resonance.
Reynolds number — A dimensionless quantity that predicts whether flow will be laminar (low value) or turbulent (high value); Stokes' law and Poiseuille's law are both valid only at sufficiently low Reynolds number. See Stokes' Method, Poiseuille's Method.
Rigidity (shear) modulus (η) — The ratio of shear stress to shear strain for an elastic solid, characterising its resistance to twisting or shape-changing deformation at constant volume. See Torsional Pendulum, Static Torsion.
Rolling without slipping — Rolling motion in which the contact point of a body has zero instantaneous velocity relative to the surface, so its linear speed and angular speed are locked together by v = rω. See Rolling Race on an Incline.
S¶
Stokes' law — The formula for the viscous drag force on a small sphere moving slowly through a fluid, proportional to the sphere's radius, its speed, and the fluid's viscosity. See Stokes' Method.
Surface tension (T) — The tendency of a liquid surface to behave like a stretched elastic membrane, arising from unbalanced intermolecular attraction at the surface. See Capillary Rise Method.
T¶
Terminal velocity — The constant speed reached by an object falling through a fluid once the net force on it (weight, buoyancy and drag combined) becomes zero. See Stokes' Method.
Transmissibility — The ratio of the force (or motion) transmitted through a vibration isolator to the force (or motion) generated by the source; the central design quantity in vibration isolation. See Vibration Isolation & Machine Mounting.
V¶
Viscosity (η) — A fluid's internal resistance to relative motion between its layers (internal friction), governing how readily it flows under an applied pressure or shear. See Poiseuille's Method, Stokes' Method.
Y¶
Young's modulus (Y) — The ratio of longitudinal (tensile or compressive) stress to strain for an elastic solid, characterising its stiffness along the direction of an applied load. See Non-Uniform Bending, Uniform Bending, Searle's Apparatus.