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)