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Abduction Movement of a segment in the frontal plane away from the midline of the body.
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Acceleration The rate at which velocity changes.
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Adduction Movement of a segment in the frontal plane toward the midline of the body.
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Afferent neuron Neuron that carries impulse toward the central nervous system; sensory neuron.
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Agonist Muscle primarily responsible for motion; prime mover.
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Angle of attack The angle between the long axis of a projected object and the direction of airflow.
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Angle of incidence The angle at which an object strikes a hard surface.
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Angle of projection The angle between the horizontal and the initial velocity vector of a projectile.
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Angle of pull The angle between the mechanical axis of bone and the line of pull of a muscle.
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Angle of reflection The angle at which an object will leave a hard surface after striking it.
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Angular acceleration The rate at which angular velocity changes.
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Angular displacement Any change in angle.
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Angular impulse A torque applied over some period of time.
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Angular momentum The quantity of angular motion a lever possesses, equal to the product of the moment of inertia and the angular velocity.
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Angular velocity The rate at which angular displacement takes place.
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Anteroposterior (AP) axis The axis that passes horizontally from front to back, perpendicular to the frontal plane.
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Archimedesâ principle Law governing buoyancy, which states that a body immersed in water is buoyed up by a force equal to the weight of the fluid displaced by the body.
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Backward tilt Pelvic motion in which the posterior surface moves somewhat backward and downward.
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Base of support Any part of the body in contact with the supporting surface and the intervening area.
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Bernoulliâs principle Law governing fluid forces, which states that when flow velocity is high, fluid pressure is low, and when flow velocity is low, fluid pressure is high.
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Bilateral axis The axis that passes horizontally from side to side, perpendicular to the sagittal plane.
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Biomechanics The study of the mechanics of biological systems.
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Boundary layer A layer of fluid that is immediately adjacent to the surface of an object.
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Buoyancy An upward force that acts to support a body immersed in water.
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Cardinal plane A primary plane, one that passes through the center of gravity.
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Center of buoyancy That point in the body at which the upward force of buoyancy acts.
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Center of gravity The âbalance pointâ of the body; the center of mass; the intersection of the three cardinal planes.
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Centrifugal force The âcenter-fleeingâ force acting on an object undergoing circular motion; a reaction force to centripetal force.
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Centripetal force The âcenter-seekingâ force constraining an object to a circular path.
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