Transcript Document
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)