chapter 3 concepts. mass mass- the amount of matter in an object units: kg, or slugs
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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)