Glossary of Terms Seating Systems as Extrinsic Enablers for Assistive Technologies

Glossary of Terms	Definitions	Examples
Center of Gravity	The point in the body at which the acceleration caused by gravity is localized.	A geometric property of any object.
Center of Pressure	Is the point where the total sum of a pressure field acts on a body, causing a force to act through that point	As an object moves through a fluid, the velocity of the fluid varies around the surface of the object.
Compression	Occurs when forces act toward each other pushing together such as the force of the vertebrate on the disks in the spinal column.	It is contrasted with tension or traction, the application of balanced outward ("pulling") forces; and with shearing forces, directed so as to displace layers of the material parallel to each other
Dampening	The ability of a material to soften on impact.	By dropping a heavy object and watching it sink into the material. If the object bounces off or just sits there...then it’s called poor dampening. Also called the 'shock absorber' feature.
Density	The ratio of the weight of a material to its volume.	Greater density means more desirable material. Low density will fatigue faster under same loading conditions.
Envelopment	The degree to which the person sinks into a seating cushion and the degree to which the cushion surrounds the buttocks.	Good envelopment creates stability and reduces peak pressures.
Equilibrium	The situation in which the force generated by one object is equal in magnitude and opposite in direction to the force generated by another object.	The condition of a system in which all competing influences are balanced.
Fixed Deformity	A permanent change taking place in the bones, muscles, capsular ligaments, or tendons that restricts the normal range of motion of the particular joint and affects the skeletal alignment of the other joint.	The toe joint cannot move normally.
Force	Anything that acts on a body to change its rate of acceleration or alter its momentum.	Is a push or pull upon an object resulting from the object's interaction with another object
Frictional Forces	Resulting forces from movement in opposite directions between two bodies in contract; may be statics or dynamic.	Is the force exerted by a surface as an object moves across it or makes an effort to move across it?
Fulcrum	The axis around which rotational movements occur.	The point on which a lever rests or is supported and on which it pivots.
Gravitational Line	The axis of the body along which the force of gravity acts.	Come from infinity and end at masses.
Linear Scan	An approach in which the selection set is organized in a linear straight line format.	A global register allocation algorithm.
Line of Application	The particular direction along which forces are applied, either pushing or pulling.	Point of application.
Mobility	The quality of being mobile.	The ability to move physically
Pelvic Obliquity	One side of the pelvis is higher than the other when viewed in the frontal plane.	The obliquity left side is lower than the right side,
Pelvic Rotation	One side of the pelvis is forward of the other side.	Forward of the other side.
Planar	Flat seating components that support the body only where it easily comes into contact with the supporting system.	Flat or level.
Pressure	Force per unit area	Compare stress.
Pressure Ulcer	A lesion that develops as a result of unrelieved pressure to an area and results in damage to underlying tissue.	A bedsore.
Recovery	The degree to which a cushion returns to its preloaded state when a load is removed.	Cushion returns.
Resilience	The ability of a material to recover its shape after a load is removed or to adjust to a load ass it is applied.	Short term recovery implies that a weight has been temporarily shifted. Long term recovery implies an overnight recovery after a cushion was loaded then unloaded. (This is a load of crock).
Rotational Movement	When the direction, distance, and time of a movement occur simultaneously, but the movement is through an angel instead of in a straight line.	Occurs around an axis.
Scoliosis	Lateral curvature of the spine.	Spine occurs when there is lateral bending of the trunk.
Shearing	Occurs when forces are parallel sliding across the surfaces such as movement that occurs as the head of the femur moves across the acetabulum during the hip.	Sliding across the surface.
Sliding Resistance	A cushion property related to friction.	Cushions with high resistance limits slides, helps to support upright posture, but makes transfers more difficult.
Stiffness	The amount a material gives under load.	The distance a person sinks into a cushion. Soft materials may bottom out, but too much stiffness may cause tissue breakdown. Sliding laterally on low stiffness is easier but the shearing forces are higher resulting in a cushion with less stability.
Stress	The resulting molecular change inside biological or non-biological materials	Molecular change.
Tension	Forces that act in the same line but away from each other pulling apart such as the force applied on the antagonist muscle during contraction of the agonist muscle.	Pulling apart.
Windswept Hip Deformity	When one hip is adducted and the other hip is abducted.	This deformity has usually been found to be the end stage of a sequence.