Kinematics and dynamics
"In physics, kinematics is the branch of mechanics concerned with the motions
of objects without being concerned with the forces that cause the motion. In this
latter respect it differs from dynamics, which is concerned with the forces
that affect motion." (from
Wikipedia: 'kinematics')
3D motion analysis needs information from both, kinematics and dynamics, depending
on the type of analysis.
Kinematics
Kinematics can be measured with optical devices like cameras which determine the
position of body landmarks over time. Cameras capture their field of view in discrete
time intervals: Normal video cameras have 25 frames per second (PAL) or 30 frames
per second (NTSC).
Kinematic stick diagram as used in motion analysis of running
High-speed cameras
often capture 100, 200, 1000 or even 20,000 frames per second but are much more
expensive than standard video equipment.
Alternatively analog sensors like goniometers (to measure angles) or accelerometers
(to measure acceleration) can be used to get kinematic information.
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Dynamics
Dynamics can be measured with analog devices like force platforms, insole measurements
or other force or pressure sensors.
Force platforms typically measure three components, i.e. forces in all spatial directions.
Pressure sensors measure forces per area and are limited to forces in perpendicular
direction.
Dynamic measurement: vertical ground reaction forces in gait
Analog-digital
converters are used to digitize the analog output voltage in order to visualize
the measured values. A/D converters also digitize the measured voltage in discrete
time intervals but with a much higher frequency than standard optical devices. Often
300 to 1000 samples per second are used but measurements with 2000 or even 10,000
Hertz (Hz) can be done with the same standard equipment. A/D converters usually
can digitize 16 or 32 channels at the same time.
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[Kinematics]
[Dynamics]
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