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Abduction Movement of a segment in the frontal plane away from the midline of the body.

Acceleration The rate at which velocity changes.

Adduction Movement of a segment in the frontal plane toward the midline of the body.

Afferent neuron Neuron that carries impulse toward the central nervous system; sensory neuron.

Agonist Muscle primarily responsible for motion; prime mover.

Angle of attack The angle between the long axis of a projected object and the direction of airflow.

Angle of incidence The angle at which an object strikes a hard surface.

Angle of projection The angle between the horizontal and the initial velocity vector of a projectile.

Angle of pull The angle between the mechanical axis of bone and the line of pull of a muscle.

Angle of reflection The angle at which an object will leave a hard surface after striking it.

Angular acceleration The rate at which angular velocity changes.

Angular displacement Any change in angle.

Angular impulse A torque applied over some period of time.

Angular momentum The quantity of angular motion a lever possesses, equal to the product of the moment of inertia and the angular velocity.

Angular velocity The rate at which angular displacement takes place.

Anteroposterior (AP) axis The axis that passes horizontally from front to back, perpendicular to the frontal plane.

Archimedes’ 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.

Backward tilt Pelvic motion in which the posterior surface moves somewhat backward and downward.

Base of support Any part of the body in contact with the supporting surface and the intervening area.

Bernoulli’s 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.

Bilateral axis The axis that passes horizontally from side to side, perpendicular to the sagittal plane.

Biomechanics The study of the mechanics of biological systems.

Boundary layer A layer of fluid that is immediately adjacent to the surface of an object.

Buoyancy An upward force that acts to support a body immersed in water.

Cardinal plane A primary plane, one that passes through the center of gravity.

Center of buoyancy That point in the body at which the upward force of buoyancy acts.

Center of gravity The “balance point” of the body; the center of mass; the intersection of the three cardinal planes.

Centrifugal force The “center-fleeing” force acting on an object undergoing circular motion; a reaction force to centripetal force.

Centripetal force The “center-seeking” force constraining an object to a circular path.


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