Introduction to Sports Biomechanics: Analysing Human Movement ...

CAUSES OF MOVEMENT – FORCES AND TORQUES
Buoyancy force The upward force exerted on an immersed body by the fluid it
displaces.
Centre of mass An imaginary balance point of a body; the point about which all of
the mass particles of the body are evenly distributed. In the context of movement
analysis, coincident with the centre of gravity.
Centre of percussion That point in a body moving about a fixed axis of rotation at
which it may strike an obstacle without communicating an acceleration (or shock)
to that axis.
Centre of pressure The effective point of application of a force distributed over a
surface.
Collinear forces Forces whose lines of action are the same.
Damping Any effect that tends to reduce the amplitude of the oscillations of an
oscillatory system.
Drag The mechanical force generated by a solid object travelling through a fluid that
acts in the direction opposite to the movement of the object; any object moving
through a fluid experiences drag. See also lift.
Ecological validity The methods, materials and setting of the experiment must
approximate the real-life circumstances that are under study. See also validity.
Energy The capacity of a system to do work. See also kinetic energy and potential
energy.
Equilibrium The state of a system whose acceleration is unchanged; a state of balance
between various physical forces. See also neutral equilibrium, stable equilibrium and
unstable equilibrium.
Force plate or platform A device that measures the contact force between an object and
its surroundings, usually the ground reaction force.
Free body diagram A diagram in which the object of interest is isolated from its
surroundings and all of the force vectors acting on the body are shown.
Integral The result of the process of integration; the area under a variable–time
curve.
Integration The mathematical process of calculating an integral.
Kinetic energy The ability of a body to do work by virtue of its motion. See also
potential energy.
Laminar flow At slow speeds the flow of a fluid smoothly over the surface of an object.
The fluid flow can be considered as a series of thin plates (or laminae, hence
the name) sliding smoothly past each other. ‘Information’ is passed between the
elements of the fluid on a microscopic scale. See also turbulent flow.
Lift The component of fluid force that acts perpendicular to the direction of movement
of an object through the fluid. Arises when the object deflects the fluid flow
asymmetrically. See also drag.
Magnus effect The curve in the path of a spinning ball caused by a pressure differential
around the ball.
Neutral equilibrium The state of a body in which the body will remain in a location
if displaced from another location. See also stable equilibrium and unstable
equilibrium.
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