UNITS AND DEFINITIONS RELATED TO BIOMECHANICAL AND ELECTROMYOGRAPHICAL MEASUREMENTS - Biomechanics and Motor Control of Human Movement - page 362

TABLE B.2 (Continued)

Name of

Physical Quantity Symbol SI Unit Definition

s − 2

Acceleration g m · Acceleration of a freely falling

body in a vacuum because of
gravity. At sea level g =

9.80665 m · s − 2 .

s − 1

Angular velocity ω rad · Time rate of change of orientation

of a line segment in a plane.

rad · s − 2 Angular acceleration α Time rate of change of angular

velocity.

Angular displacement θ radian (rad) Change in orientation of a line

segment, which is given by the
plane angle between initial and
final orientations.

Period T second (s) Time to complete one cycle of a

periodic event or, more
generally, time duration of any
event or phase of an event.

Frequency f hertz (Hz) Number of repetitions of a

periodic event that occurs in a
given time interval. 1 Hz
equals 1 repetition or cycle per
second. (1 Hz

1s − 1 )

=

m − 3 Density ρ kg · Mass per unit volume of an

object or substance.

Specific gravity d Ratio of the density of a

substance to the density of
water at 4 ◦ C.

Force F newton (N) Effect of one body on another

that causes the bodies to
accelerate relative to an inertial
reference frame. 1 N is that
force that, when applied to 1 kg
of mass, causes it to accelerate
at 1 m

s − 2 in the direction of
the force application relative to
the inertial reference frame.
(1 N = 1kg · m · s − 2 .)

·

Weight G N Force exerted on a mass because

of gravitational attraction;
equal to the product of the
mass of the body and the
acceleration from gravity. ( G
= m · g .)