chapter 3 concepts. mass mass- the amount of matter in an object units: kg, or slugs
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Chapter 3 Concepts
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Mass
Mass- the amount of matter in an object Units: Kg, or Slugs
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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
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Kinematics
Measure of movement using:– Displacement– Velocity– Acceleration– Angles
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Kinetics
Measure of the outcomes of movement using forces
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Static
Non-moving situations– Forces are balanced– Example:
• Friction pushing force and resistance force are equal
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Dynamic
Moving situation– Forces are unbalanced so movement results
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Qualitative
Analysis of movement using observation and words to describe the movement
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Quantitative
Analysis of movement using discreet analysis and numbers to describe the moment.
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Units of Measure-
See Table 3.1 pg 70
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Planes of motions
Transverse plane Longitudinal axis
Example twisting motion
Sagittal plane Mediolateral axis
Walking, somersaulting
Frontal plane Antero-posterior axis
Cartwheel, jumping jacks
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Definition of contractions
Concentric Isometric Eccentric
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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.
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FORCE
Force-– = mass * acceleration– = mass * gravity
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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?
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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?
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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?
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Volume
Volume = length*width*height Units: m3
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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?
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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?
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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
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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).
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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).
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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)