Basic Dimensions
Linear Kinetics
„
„
CHAPTER 3
Need common units of measure for
quantitative analysis
Qualitative variables have quantitative
counterparts
„
„
„
„
LENGTH
TIME
SPACE
OTHERS
LENGTH
„
„
Describes position in
space
Critical component of
sport
1)
2)
3)
4)
5)
„
„
„
„
Mass
Inertia
Weight
Force
Length, Time, & Mass are the BASIC
dimensions used in mechanics
„
„
„
Everything else is derived from these 3
Important dimension in
sport
Performance measure
„
Anthropometrics
Equipment
Dimension of sport
International system
used
METER (m)
Other Descriptors
„
TIME
„
„
Initial or start time
Final or end time
SECONDS (s)
MASS (m)- quantity of matter
composing a body
„ WEIGHT (N or lb)- gravitational force
acting on a body; proportional to m …
wt = mag
„ INERTIA - resistance to action, change,
to move; directly proportional to mass
„ FORCE - push or pull acting on a body;
magnitude direction & point of
application
„
1
FORCE
„
any interaction (push or
pull) between two objects
that can cause an object to
accelerate either + or „ magnitude (vector)
„ direction (angle)
„ pt. of application
„ line of action
Law of Inertia
„
A body will maintain a state of rest or
constant velocity unless acted on by an
external force that changes the state
„
Principle of Conservation of Momentum
Mechanical Behavior of Bodies in
Contact
Newton:
When two bodies undergo a direct collision, the
difference in their velocities immediately after
impact is proportional to the difference in their
velocities immediately before impact
-e = relative velocity after impact = v1 - v2
relative velocity before impact
u1 - u2
NEWTON’S LAWS
„
Sir Isaac Newton
„
„
„
„
Born the year
Galileo died
Cambridge
educated
The Black Plague
1686 ~ Principia
Mechanical Behavior of Bodies in
Contact
Linear Momentum: Quantity of Motion
„ M = mv
„ Units - kg • m/s
Principle of conservation of momentum:
In the absence of external forces, the
total momentum of a given system
remains constant
Mechanical Behavior of Bodies in
Contact
Impact:
Perfectly elastic impact: -e ≈ 1
Perfectly plastic impact: -e ≈ 0
Coefficient of restitution:
Absolute value of the ratio of the v of
separation to the v of approach
2
Law of Acceleration
„
A force applied to a body causes an
acceleration of that body of a magnitude
proportional to the force, in the direction of
the force, and inversely proportional to the
body’s mass
„
F = ma
~or~
a= F/m
Mechanical Behavior of Bodies in
Contact
Impulse:
„ Impulse = Ft
Derived from Newton’s Second law:
„ F = ma
„ F = m ([v2 - v1] / t)
„ Ft = (mv2) - (mv1)
„ Ft = ∆M
Law of Reaction
„
For every action, there is an equal and
opposite reaction
„
When one body exerts a force on a second,
the second body exerts a reaction for that
is equal in magnitude and opposite in
direction of the first body
Law of Gravitation
„
All bodies are attracted to one
another with a force proportional
to the product of the masses and
inversely proportional to the
square of the distance between
them
„
Fg = G(m1m2 / d2)
3