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 in 2 = 100 psi or lbs/in 2 –100 lbs/25 in 2 = 25 psi or lbs/in 2 – What is the difference between stepping on grass on high heels versus tennis shoes?

Volume Volume = length*width*height Units: m 3

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 = P final - P initial ). 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 = (P final - P initial ) / 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 = (V final - V initial ) / time instantaneous A = (V final - V initial ) / time (where time is very short). Units of acceleration - meters per second per second (m/s 2 ), feet per second per second (ft/s 2 )