aerofoil an object with a shape that generates lift in a moving fluid
angle of attack angle between the longitudinal axis of an object and the relative direction of fluid flow
angle of incidence angle between the path of an object and a line drawn perpendicular from the surface with which it is presently in contact (i.e. the normal line)
angle of reflection angle between the path of an object and a line drawn perpendicular from the surface from which it has rebounded (i.e. the normal line)
angular concerned with rotation about a line or point
angular acceleration rate of change of angular velocity; equal to angular velocity per unit time
angular displacement change in angular position or the orientation of a straight segment
angular impulse product of torque and time (torque produced over a period of time); equal to the change in angular momentum of an object
angular momentum product of the moment of inertia and angular velocity; angular analogue of linear momentum
angular velocity rate of change in angular displacement; equal to angular displacement per unit time
anteroposterior axis imaginary line projecting from the front to the back of an object, about which frontal plane motion occurs
axis of rotation imaginary line passing through the centre of rotation; perpendicular to the plane of rotation
base of support area under a person or object that includes all points of contact between the person/object (e.g. hands, feet, or other) and the surface/ground
biomechanics field of science devoted to understanding mechanical principles in relation to biological organisms
boundary layer layer of fluid immediately surrounding an object
braking impulse product of the applied force and the time over which it is applied acting to slow an object (often occurs at foot-strike in running)
buoyancy the tendency for an object to float in a fluid, caused by the buoyancy force which is directly proportional to the submerged volume of the object; flotation occurs when the buoyancy force equals or exceeds the weight force of the object
centre of buoyancy point about which the sum of buoyancy forces acts (equivalent to the centre of volume)
centre of gravity point about which the sum of torques of all point weights (that is, mass × gravity) of a body equals zero; the body can balance at this point
centre of mass point about which the sum of torques of all point weights of a body would be zero if oriented perpendicular to the line of gravity
centre of pressure point of application of a force vector, e.g. the point of ground reaction force measured at the feet during standing or locomotion
coefficient of drag numerical index of the resistance generated when a body moves through a fluid (values greater than 0)
coefficient of friction numerical index of the likelihood that two surfaces in contact will not slide past each other (values greater than 0)
coefficient of restitution numerical index of elasticity (energy retained) after a collision of two bodies (values 0–1)
coefficient of variation standard deviation (variability) of a series of measurements relative to the mean of the measurements
curvilinear curved path
displacement quantity describing the change in position of an object from a beginning to end point, without concern for the total length of the path travelled
distance sum total of all displacements of an object without reference to resultant direction
dynamics area of mechanics associated with systems subject to acceleration
efficiency ratio of the input to output of a system; often refers to ratio of energy in to energy out
external work a force is applied by a source external to a body (or system) causing a displacement of the body
field of view total area seen by a camera with a given zoom specification
fluid substance that flows when a force is applied; molecules can move past each other
force product of mass and acceleration; induces a change in the mobile state of an object
form drag (profile/pressure drag) regarding resistance caused by a difference in pressure between the front and back of an object; proportional to the frontal surface area and shape (coefficient of drag) of an object and to the square of the velocity difference between the object and fluid
friction force opposing motion at the interface of two surfaces
frontal plane imaginary plane in which lateral movement of parts of a body, or the body itself, occurs
gait an animal’s manner of locomotion, commonly referring to walking in humans, but also referring to running, skipping and others
general motion motion where translation and rotation occur simultaneously
gravitational force force exerted by one object on another that accelerates the mass at a rate proportional to the combined masses but is inversely proportional to the distance between them
heart rate reserve (HRR) difference between resting and maximum heart rates
impulse product of applied force and the time over which it is applied
impulse–momentum relationship relationship between impulse and momentum; the momentum of an object will change in proportion to the sum of applied impulses
inertia tendency for a body to remain in its present state of motion
initial velocity a description of the speed and direction of an object at a pre-defined starting point
instantaneous occurring immediately, at a single, discrete point in time
internal work one part of a body or system applies a force on another part of the body, causing a displacement
kinematics describing how an object moves with respect to time; its pattern or sequencing of movement
kinetic chain linked segments of a body that move together
kinetic energy the energy associated with motion; equal to the product of half an object’s mass and the square of its velocity
laminar flow fluid flow characterised by parallel layers of fluid
lift a force acting on a body perpendicular to its movement through a fluid; created by a ‘turning’ of fluid flow
linear straight or curved but not circular (rotational) path
linear acceleration rate of change of linear velocity; equal to angular velocity per unit time
linear displacement change in linear position or the orientation of a straight segment
linear momentum product of the mass and linear velocity of an object; proportional to the impulse applied to an object
linear velocity rate of change in linear displacement; equal to linear displacement per unit time
longitudinal axis imaginary line projecting from the top to the bottom of an object about which transverse plane motion occurs
Magnus effect changing of trajectory of an object towards the direction of spin; results from the Magnus force
Magnus force lift force acting on a spinning object
mass quantity of matter in an object
mechanics area of physics exploring the effects of forces on particles and systems
mechanical energy sum of an object’s kinetic and potential energies
mediolateral axis imaginary line projecting sideways across (or through) an object about which sagittal plane motion occurs
metabolic energy energy liberated through cellular processes; can be used to do mechanical work
moment pertaining to an action at a distance, for example moment of inertia, moment of force
moment arm perpendicular distance between a centre of rotation of an object and the line of action of a force acting on the object
moment of inertia tendency for a rotating body to remain in its present state of motion; equal to the product of the mass of an object and its radius of gyration
moment of force (torque) the result of a force acting at a distance from a centre of rotation; rotational action of a force
normal reaction force force acting perpendicular to a surface
parabolic flight curved flight path of a projectile occurring in zero-drag conditions; upward and downward paths are of identical shape
parallax error error of size or distance (and its time derivatives) associated with an object’s movement across the field of view or that of a camera
parallel axes theorem theorem allowing the calculation of the total moment of inertia of a rotating object, incorporating inertia about its remote (that is, about an end point) and local (that is, about its own rotational centre) axes
perspective error error of size or distance (and its time derivatives) associated with an object’s distance from the eyes or a camera
potential energy energy associated with an object’s position in a gravitational field; it is often defined as the product of an object’s mass, the gravitational force and its height above a defined surface, but other forms of potential energy exist (e.g. elastic, magnetic)
power rate of doing work; work per unit time or the product of force and velocity
pressure force per unit area
principal axes three imaginary perpendicular axes passing through a body’s centre of mass
projectile (motion) object in free motion subjected only to the forces of gravity and air resistance
projection angle angle relative to a defined surface (usually the ground) at which an object is projected
projection height vertical difference between the projection and landing heights
projection speed initial speed of a projectile
projection velocity initial speed and direction of a projectile
propulsive efficiency ratio of the amount of force (power) that results in overcoming drag relative to the total force (power) production of a body moving in a fluid environment; the remaining force (power) accelerates the fluid
propulsive impulse product of the applied force and the time over which it is applied acting to accelerate an object
push-like movement pattern pattern of movement whereby the joints of linked segments extend (or flex) simultaneously; optimum pattern for high forces and accuracy
qualitative non-numeric description
quantitative numeric description
radian unit of angular displacement equal to the angle covered when a line joining the centre of a circle to the perimeter is rotated by the length of one radius; equal to 57.3°
radius of gyration distance from the axis of rotation to a point where the centre of mass of the object could be located without altering its rotational characteristics
range horizontal displacement of an object from projection to landing
rectilinear straight path
recovery phase period during which an appendage is repositioned from the back to the front of the body in preparation for the swing phase
relative velocity difference in velocities of two objects or media (for example, object and fluid)
rotation circular (non-linear) motion or motion about an axis of rotation
sagittal plane imaginary plane in which anteroposterior (front-to-back) movement of parts of a body, or the body itself, occurs
scaling factor relationship between arbitrary units and real-world units; arbitrary per real-world unit
shear force force directed parallel to a surface
sliding friction (kinetic friction) force opposing motion between two surfaces that are in contact and in motion relative to each other
speed rate of change of distance, without reference to direction
static friction force opposing motion between two surfaces that are in contact but are not moving relative to each other
statics branch of mechanics examining systems, either at rest or in motion, in which balanced forces are acting
surface drag (skin friction, viscous drag) retarding resistance caused by a friction between an object’s surface and a fluid moving relative to it
swing phase period during which an appendage is repositioned from the front to the back of the body; usually associated with the application of propulsive force
throw-like movement pattern pattern of movement whereby the joints of linked segments extend (or flex) in a sequential order, usually proximo-distally; optimum pattern for the attainment of high movement speeds
trajectory flight path of a projectile
translation linear motion
transverse plane imaginary plane in which horizontal rotational movement of parts of a body, or the body itself, occurs
vector physical quantity described by both magnitude and direction
wave drag retarding resistance caused by pressure differences around an object moving at the interface of two fluids (for example, air and water) that results in wave formation in the more dense fluid
work product of force and displacement; force provided over a range of object movement. Can be ‘internal’, produced by our own muscles, or ‘external’, the product of an external force
work–energy relationship the change in energy of a body or system is directly proportional to the work done on the object or system; both work and energy have the same unit of measurement (joule).