Abrasion
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The process of scuffing, scratching, wearing down, marring, or rubbing away. It can be intentionally imposed in a controlled process using an abrasive.
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By reducing particle size.
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Angular Momentum
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Angular momentum is the rotational counterpart of momentum. A spinning flywheel has angular momentum.
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Auxetic Materials
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Materials which, when stretched, become thicker perpendicularly to the applied force, i.e. they have a negative Poisson's ratio. Such materials have interesting mechanical properties such as high energy absorption and fracture resistance. This may be useful in applications such as body armor, packing material, knee and elbow pads, robust shock absorbing material and sponge mops.
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Centrifugal Force
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An outward force associated with rotation. Centrifugal force is one of several so-called pseudo-forces (or inertial forces), so named because, unlike real forces, they do not originate in interactions with other bodies situated in the environment of the particle upon which they act. Instead, centrifugal force originates in the rotation of the frame of reference within which observations are made.
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Compression
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The result of the subjection of a material to compressive stress, resulting in reduction of volume. The opposite of compression is tension. In simple terms, compression is a pushing force.
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Converse Piezoelectric Effect
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Materials exhibiting the direct piezoelectric effect (the production of electricity when stress is applied) also exhibit the converse piezoelectric effect (the production of stress and/or strain when an electric field is applied). For example, lead zirconate titanate crystals will exhibit a maximum shape change of about 0.1% of the original dimension.
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Decomposition (biological)
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The break down of tissue of a formerly living organism into simpler forms of matter.
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Deformation
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A change in the shape or size of an object due to an applied force. This can be a result of tensile (pulling) forces, compressive (pushing) forces, shear, bending or torsion (twisting). Deformation is often described in terms of strain.
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Detonation
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Detonation involves a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations are observed in both conventional solid and liquid explosives, as well as in reactive gases.
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Displacement
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Displacement occurs when an object is immersed in a fluid, pushing the fluid out of the way and taking its place. The volume of the fluid displaced is equal to the volume of the object imersed. An object that sinks, or is otherwise fully immersed, displaces an amount of fluid equal to its total volume.
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Drag
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A drag (sometimes called fluid resistance) is the force that resists the movement of a solid object through a fluid (a liquid or gas). The most familiar form of drag is made up of friction forces, which act parallel to the object's surface, plus pressure forces, which act in a direction perpendicular to the object's surface.
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Elastic Recovery
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The tendancy of a material that has been stretched to return to its original shape.
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Elasticity
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The physical property of a material when it deforms under stress (e.g. external forces), but returns to its original shape when the stress is removed. The amount of deformation is called the strain. The elastic regime is characterized by a linear relationship between stress and strain, denoted linear elasticity.
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Electret
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An Electret is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet.
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Electric Field
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The space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field (that can also be equated to electric flux density). This electric field exerts a force on other electrically charged objects.
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Electrohydrodynamics
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Includes the following types of particle and fluid transport mechanisms:Electrophoresis, electrokinesis, dielectrophoresis, electro-osmosis, and electrorotation. In general, the phenomena relate to the direct conversion of electrical energy into kinetic energy, and vice versa.
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Electromagnetic Induction
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The generation of electromotive force (EMF) in a current-carrying conductor exposed to a changing magnetic field
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Electrorheological Effect
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Electrorheological (ER) fluids are suspensions of extremely fine non-conducting particles (up to 50 micrometres diameter) in an electrically insulating fluid. The apparent viscosity of ER fluids changes reversibly by an order of up to 100,000 in response to an electric field. A typical ER fluid can go from the consistency of a liquid to that of a gel, and back, with response times of the order of ms. Sometimes called the Winslow Effect.
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Electrostatics
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The phenomena arising from stationary or slowly moving electric charges
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Electrostriction
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A property of all electrical non-conductors, or dielectrics, that causes them to change their shape under the application of an electric field. All dielectrics exhibit some electrostriction, but certain engineered ceramics, known as relaxor ferroelectrics, have extraordinarily high electrostrictive constants,e.g. Lead magnesium niobate (PMN), Lead magnesium niobate-lead titanate (PMN-PT), Lead lanthanum zirconate titanate (PLZT).
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Entropic Explosion
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An explosion in which the reactants undergo a large change in volume without releasing a large amount of heat.
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Explosion
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A sudden increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases.
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Ferromagnetism
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The mechanism by which certain materials (such as iron) form permanent magnets and/or exhibit strong interactions with magnets. Responsible for commonly observed magnetism phenomena, e.g. 'fridge magnets. A material is 'ferromagnetic' only if all its magnetic ions add a positive contribution to the net magnetisation. If some of them subtract from the net magnetisation (i.e. are partially anti-aligned), then the material is 'ferrimagnetic'.
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Fluidisation
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A process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurs when a fluid (liquid or gas) is passed up through the granular material. When fluidized, a bed of solid particles will behave as a fluid, like a liquid or gas.
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Force
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That which can cause an object with mass to accelerate. Force has both magnitude & direction, i.e. it's a vector quantity. An object with constant mass will accelerate in proportion to the net force acting upon it and in inverse proportion to its mass (or the net force on an object is equal to the rate of change of momentum it experiences). Forces acting on objects may cause them to rotate or deform, or result in a change in pressure.
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Forced Convection
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Heat advection by a fluid which is not due to the natural forces of buoyancy induced by heating. In forced heat convection, transfer of heat is due to movement in the fluid which results from many other forces, such as (for example) a fan or pump.
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Gravitation
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A natural phenomenon by which objects with mass attract one another. In everyday life, gravitation is most commonly thought of as the agency which lends weight to objects with mass.
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Helix
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A special kind of space curve, i.e. a smooth curve in three-space. A helix is characterised by the fact that the tangent line at any point makes a constant angle with a fixed line.
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Holes
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A hole is a confined lack of structure in some part of an object.
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Impact Force
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A high force or shock applied over a short time period. Such a force or acceleration can sometimes have a greater effect than a lower force applied over a proportionally longer time period.
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Inertia
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The resistance of any physical object to a change in its state of motion or rest. It is proportional to an object's mass.
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Length Contraction
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The physical phenomenon of a decrease in length detected by an observer of objects that travel at any non-zero velocity relative to that observer. This contraction is usually only noticeable at a substantial fraction of the speed of light; the contraction is only in the direction parallel to the direction in which the observed body is travelling.
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Lever
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A rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force that can be applied to another object.
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Lorentz Force
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The force on a point charge due to electromagnetic fields. When a wire carrying an electrical current is placed in a magnetic field, each of the moving charges, which comprise the current, experiences the Lorentz force, and together they can create a macroscopic force on the wire (sometimes called the Laplace force).
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Magnetic Field
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A vector field which surrounds magnets and electric currents, and is detected by the force it exerts on moving electric charges and on magnetic materials. When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field. Magnetic fields also have their own energy with an energy density proportional to the square of the field intensity.
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Magnetism
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One of the phenomena by which materials exert attractive or repulsive forces on other materials. Some well-known materials that exhibit easily detectable magnetic properties (called magnets) are nickel, iron, cobalt, and their alloys; however, all materials are influenced to greater or lesser degree by the presence of a magnetic field.
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Magnetoelastic Effects
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A group of effects including Magnetostriction (or Joule Magnetostriction), Delta-E Effect, Wiedemann Effect, Magnetovolume Effect, and their Inverses: Villari Effect, Delta-E Effect, Matteucci Effect and the Nagaoka-Honda Effect.
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Magnetostriction
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A property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetisation. The variation of material's magnetisation due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value. This effect can cause losses due to frictional heating in susceptible ferromagnetic cores.
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Magnetovolume Effect
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One of a group of Magnetoelastic Effects. Volume change due to magnetisation (most evident near the Curie temperature)
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Mechanical Force
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A mechanical influence that causes a free body to undergo an acceleration.
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Negative Thermal Expansion
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A physicochemical process in which some materials contract upon heating rather than expanding as most materials do. Materials which undergo this unusual process have a range of potential engineering, photonic, electronic, and structural applications. For example, mixing a negative thermal expansion material with a 'normal' material which expands on heating, could result in a zero expansion composite material.
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Pascal's Law
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(or the Principle of transmission of fluid-pressure) Pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio (initial difference) remains same.
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In the case of a divided solid dispersed within a liquid.
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Physical Containment
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Partial or complete enclosure of an object or substance by some physical medium, typically for the purpose of protection or restriction of movement.
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Piezoelectric Effect
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Generation of electrical charge in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical strain. The piezoelectric effect is a reversible process in that materials also exhibit the reverse piezoelectric effect (the internal generation of a mechanical force resulting from an applied electrical field).
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Piezomagnetism
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A phenomenon observed in some antiferromagnetic crystals. It is characterised by a linear coupling between the system's magnetic polarisation and mechanical strain. In a piezomagnetic, one may induce a spontaneous magnetic moment by applying physical stress, or a physical deformation by applying a magnetic field. Piezomagnetism differs from the related property of magnetostriction.
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Plasticity
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The deformation of a material undergoing non-reversible changes of shape in response to applied forces. For example, a solid piece of metal or plastic being bent or pounded into a new shape displays plasticity as permanent changes occur within the material itself.
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Poisson's Effect
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When a material is compressed in one direction, it usually tends to expand in the other two directions perpendicular to the direction of compression.
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Pressure Increase
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Pressure is an effect which occurs when a force is applied on a surface. Pressure is transmitted to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point.
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Pressurisation
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The application of pressure in a given situation or environment; and more specifically refers to the process by which atmospheric pressure is maintained in an isolated or semi-isolated atmospheric environment (for instance, in an aircraft, or whilst scuba diving).
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Pseudoelasticity
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(or superelasticity) An elastic (impermanent) response to relatively high stress caused by a phase transformation between the austenitic and martensitic phases of a crystal. Exhibited in Shape memory alloys. Superelastic alloys belong to the larger family of shape memory alloys. Unlike shape-memory alloys, no change in temperature is needed for the alloy to recover its initial shape.
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Reaction (physics)
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In classical mechanics, Newton's third law states that forces occur in pairs: the Action and the Reaction. Both forces are equal in magnitude and opposite in direction. The distinction between action and reaction is purely arbitrary: any one of the two forces can be considered an action, in which case the other (corresponding) force automatically becomes its associated reaction.
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Sedimentation
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The motion of molecules in solutions or particles in suspensions in response to an external force such as gravity, centrifugal acceleration or electromagnetism. Sedimentation may pertain to objects of various sizes, ranging from suspensions of dust and pollen particles to cellular suspensions to solutions of single molecules such as proteins and peptides.
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Settling
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The process by which particulates settle to the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force. For gravity settling, this means that the particles will tend to fall to the bottom of the vessel, forming a slurry at the vessel base.
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Shock Wave
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A type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium (solid, liquid, gas or plasma) or through a field such as the electromagnetic field. Characterized by an abrupt, nearly discontinuous change in the characteristics of the medium. Associated with rapid rise in pressure, temperature and density of the flow. A shock wave travels through most media at a higher speed than an ordinary wave.
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Sound
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A mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard.
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Surface of Constant Width
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A convex form whose width, measured by the distance between two opposite parallel planes touching its boundary, is the same regardless of the direction of those two parallel planes. The three-dimensional analogue of a curve of constant width, a two-dimensional shape with a constant distance between pairs of parallel tangent lines. A sphere is obviously a surface of constant width, but there are others, such as Meissner Bodies.
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Thermal Contraction
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The tendency of matter to reduce in volume (contract) in response to a change in temperature or when a substance is cooled.
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Thermal Expansion
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The tendency of matter to change in volume in response to a change in temperature or when a substance is heated.
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Torque
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Torque (also called moment or moment of force) is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist. Torque is the rotational analogue of Force.
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Ultrasonic Vibration
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Vibration at ultrasonic frequencies.
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Through settling.
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Ultrasound
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Cyclic sound pressure with a frequency greater than the upper limit of human hearing. Although this limit varies from person to person, 20 kHz serves as a useful lower limit in describing ultrasound.
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Vibration
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Mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.
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Through settling.
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Viscoelasticity
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The property of exhibiting both viscous and elastic characteristics when undergoing deformation.
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Wear
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The erosion of material from a solid surface by the action of another surface.
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Through closer packing of finder particles.
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