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Chapter 3 Concepts
Mass
 Mass-
the amount of matter in an
object

Units: Kg, or Slugs
Inertia

Inertia- the resistance to a change in motion.
• The tendency to remain still if already still
• The tendency to remain in motion if already in
motion
Kinematics

Measure of movement using:
–
–
–
–
Displacement
Velocity
Acceleration
Angles
Kinetics

Measure of the outcomes of movement
using forces
Static

Non-moving situations
– Forces are balanced
– Example:
• Friction pushing force and resistance force are equal
Dynamic

Moving situation
– Forces are unbalanced so movement results
Qualitative

Analysis of movement using observation
and words to describe the movement
Quantitative

Analysis of movement using discreet
analysis and numbers to describe the
moment.
Units of Measure
See Table 3.1 pg 70
Planes of motions

Transverse plane
 Longitudinal axis
 Example twisting motion

Sagittal plane
 Mediolateral axis
 Walking, somersaulting

Frontal plane
 Antero-posterior axis
 Cartwheel, jumping jacks
Definition of contractions



Concentric
Isometric
Eccentric
Types of contractions





Concentric - muscle is shortening as it contracts.
External force is less than muscle contraction
force.
Isometric- muscle stays the same length as it
contracts. External force is equal to muscle
force.
Eccentric- muscle stretches as it contracts.
External force is greater than muscle force.
FORCE

Force– = mass * acceleration
– = mass * gravity
WEIGHT
• Weight= mass * gravity
• Units: Newtons (N), Lbs
• Weight is a Vector because gravity has a direction
towards the center of the earth.
• What is the difference between mass and weight?
Center of Gravity

Center of Gravity– The point about which an object’s mass is
distributed.
• Can an object have a center of gravity that is outside
of itself?
Pressure

Pressure = weight/ area
 The
greater the area the less force is applied
over any particular portion of the area.
– 100 lbs/ 1 in2 = 100 psi or lbs/in2
– 100 lbs/25 in2 = 25 psi or lbs/in2
–
What is the difference between stepping on grass on high heels
versus tennis shoes?
Volume

Volume = length*width*height

Units: m3
Density

Density = weight/volume
– Flotation=
– Whether something floats or sinks depends on whether
the object trying to float is more or less dense than the
substance it is floating in.
• Question: Why might the same person float in salt water ( the
ocean) but not in fresh water?
TORQUE

Torque = Force * moment arm
– Moment arm = the perpendicular distance from
the axis of rotation to the point of force
application.
– Units: ft-lbs, N-m
– What two methods can be used to increase
Torque?
Impulse

Impulse = Force * time

Units: N-s, Lb-s

Impulse= change in momentum
 Force = (mv2-mv1)/t
• If the time of impact increases then the force of impact
decreases
• Implications for sports equipment
– Safety nets
– Padding
– Landing pits
Position / Displacement

Position (P) - the location of particle (body
landmark, body c.g.) in space, measured with
respect to a fixed reference system. (Position is a
vector).
 Displacement (D) - the change in position of a
particle (over a specified time interval).
 D = Pfinal - Pinitial).
 Distance - the linear length covered over a
specified time period. (Distance is a scalar).
Velocity





Velocity (V) - the rate of change of position of a
particle.
average V = (Pfinal - Pinitial) / time
average V = D / time
instantaneous V = D / time (where time is
extremely short).
Units of velocity - feet per second (ft/sec), meters
per second (m/sec), miles per hour (mi/hr).
Acceleration

Acceleration (A) - the rate of change of velocity of
a particle.
 average A = (Vfinal - Vinitial) / time
 instantaneous A = (Vfinal - Vinitial) / time (where
time is very short).
 Units of acceleration - meters per second per
second (m/s2), feet per second per second (ft/s2)