KHS 301 Exam 2

Energy

The ability to perform work

Mechanical Energy

kinetic and potential energy

Conservation of Energy

energy cannot be created or destroyed; but can be transferred from one form to another

Mechanical Work

Product of force exerted on object x displacement of object at the point of force application along line of action of force

- Transfer of energy

- Scalar quantity - Joules

average force x displacement and delta energy

Work equations

work = force x displacement x cosθ

If force applied is not along the same axis as the displacement then: (equation)

Positive Work

Done by a force acting on an object if the object is displaced in same direction as force

- person transfers energy into a system

Negative Work

Done by a force acting on an object if the object is displaced in opposite direction as force

- system transfers energy into a person

0 J

Net Work of positive and negative work = ?

Physiological Work

Energy is used to move, maintain body temp, digest, etc.

increases

Dynamic muscle actions - CON & ECC phases = BLANK PW

increases

Isometric muscle actions - no mechanical work - BLANK PW

energy expenditure

Skeletal Muscle Contractility increase BLANK BLANK

Linear Kinetic Energy

Energy due to motion of an object

• Work needed to accelerate a given mass from rest to its stated velocity

• Object in motion has ability to perform work on another object

Δ KE

Work Done =

1/2mv^2

KE (mass and velocity) =

(Momentum)^2 / 2m

KE (momentum) =

KEL + KEA

Total KE =

Elastic Collision

conservation of KE

Inelastic Collision

some KE lost as sound & heat energy

Potential Energy

Energy stored within an object due to its vertical position or deformation

- Scalar Quantity - J

- 2 Types

-- Gravitational PE

-- Strain Energy

Gravitational Potential Energy

Potential energy due to an object's position relative to earth

• Related to object's weight & height above ground

- PE = W x h or PE = mg x h

w x h, mg x h

Potential Energy Equations (2) =

Strain/Elastic Energy

Energy due to deformation of an object

- "spring" like property

- Related to object's stiffness, material properties, & deformation

- SE = ½ kΔx2

1/2 kΔx2

SE equation

arrow

Archer deforms bow by pulling string - bow possesses potential to perform work on BLANK

Pole Vault

Maximize transfer KE to PE

Phase 1: pole bends = increase storage of SE

Phase 2: pole bends = release of strain energy

pole composition and length, pole stiffness, athlete strength and power

Key elements of pole vault

Prosthetics

Transtibial amputations with passive-elastic carbon-fiber running-specific prostheses with custom sockets

Spring-like: store & return ME during 1st & 2nd half of ground contact

Advantages of Prosthetics

1. Weigh Less (abt 1.8 kg per leg) = decrease moment of inertia

2. Don't fatigue or require mechanical energy

3. Act as viscoelastic spring but running economy is same

4. Similar ground contact time/speed

5. increase stride frequency, decrease swing time

6. Bilateral greater economy than unilateral (one fake leg)

7. Stiffness of prosthetics affects speed: increase stiffness = increase speed

Disadvantages of Prosthetics

1. Can't fully replicate leg function - i.e. muscle contraction, neural stimulation

2. Alters running biomechanics (stride kinematics/kinetics) dependent on fit

3. May force knee/hip muscles to provide increase GRF to maintain gait (12% decrease GRF at 4.5 m/s)

Young's Modulus

measure of CT stiffness

- Linear region

- MPa, N/mm^2

E= FLo/ AoΔL

FLo/ AoΔL

Young's Modulus (CT Stiffness) Equation

stiffness, CSA

Training can increase BLANK and BLANK

Elastic Bands

Ascending Strength Curves

- ForceE = kx

k - stiffness constant; x - length change

kx

Elastic force equation:

Conservation of Mechanical Energy

• The total ME of an object is constant if no external forces other than gravity act on the object

• Total ME = KE (linear & angular) + PE (g or strain)

KE + PE

Mechanical Energy equation

Potential Energy and Kinetic Energy Relationship

potential energy transforms into kinetic energy, and kinetic energy converts into potential energy, and then back again

- When they level out it creates a constant

Potential Energy

Strain energy is equal to BLANK BLANK

Kinematics

the branch of dynamics concerned with the description of motion

Motion

the process of changing position

Motion Analysis

• Science of comparing sequential skill images captured from photo graphing a body in motion

• Calculate angular & linear displacement, distance, joint position & ROM, velocity, speed, acceleration, 2D/3D

Two-Dimensional Motion Analysis

• X & Y axes

• Frames = 50-60 Hz

• Qualitative analyses, limited quantitative analyses

• Calibration - reference object (1m) captured in view & converted to pixels

Calibration in 2D

reference object (1m) captured in view & converted to pixels

Three-Dimensional Motion Analysis

• Multiple cameras - x, y, & z axes

• High-speed cinematography- 100 to > 500 Hz

• Calibration: reference static or dynamic objects of known dimension with multiple markers

Calibration in 3D

reference static or dynamic objects of known dimension with multiple markers

Preferred for Motion Analysis

3D Motion Analysis

Digitization

Conversion of parts of image to numerical position data (frame-by-frame)

- Manual - cursor is moved, "clicked", & marked

- Automatic - reflective markers are automatically defined

Manual Digitization

cursor is moved, "clicked", & marked

Automatic Digitization

reflective markers are automatically defined

How many Data points/sec would be generated at 50 Hz with using 15 markers?

750 data pts/sec

Linear Motion (Translation)

all points on body or object move same distance, in the same direction, at the same time

- Rectilinear

- Curvilinear

Rectilinear

linear motion

Curvilinear

curved pathway

Example of a Curvilinear Motion?

Long Jump

Angular Motion (Rotational, Rotary)

all points on a body or object move in circles about same axis

Examples of Angular Motion

- Isolated limb movements

- Somersault

- Ball rotation

- Golf drive

- Baseball/softball swing

General Motion

Combining Angular and Linear Motion

Examples of General Motion

extension of knee (angular) & flexion of hip (angular) produces linear motion of body

Linear Kinematics

- Position

- Displacement and Distance

- Speed and Velocity

- Acceleration and Deceleration

Position

• "Location in space"

• Describes object location in athletics

- Position of players, position during running, jumping, throwing, lifting, joint or body segment position (ROM)

• Coordinate system (reference system)

Cartesian plane (coordinate plane)

Consists of origin, x & y axis, & a coordinate point (X,Y) in 2-D plane, + axis (Z) in 3-D

- Rene Descartes

- Used to coordinate position

Distance

measure of total length of path followed

Displacement

straight-line length in a specific direction from initial to final position

- Vector quantity

Speed

rate of motion in relation to distance"

Speed Equation

Δ distance / time (m/sec)

Velocity

"rate of motion in a specific direction in relation to displacement"

Velocity Equation

Δ displacement / time (m/sec)

- Vector quantity

instantaneous speed

The rate at which an object is moving at a given moment in time

Phases of Sprinting

Acceleration, Maximum Speed, Deceleration

Velocity

• Average velocity = displacement / time (m/sec)

- Vector quantity

Baseball, reaction time of a hitter needed to hit a pitch of 90 mph from 60.5 feet (the ball is released 2.5 feet in front of mound)

- Calculate time

0.44 seconds

Application: GPS/LPS - Player Load Monitoring

Uses combo of inertial measurement units (accelerometers, magnetometer, gyroscopes) & satellites to triangulate athlete's position - 10 Hz

• Running/cycling distance, velocity/speed, acceleration, deceleration, jumps, COD, impact

Load Monitoring

Internal (RPE, HR, BP, HRV, biochem markers)

Vs.

External (key performance indicators [KPI])

- Tracking software daily, weekly, monthly, yearly

Internal Load Monitoring

RPE, HR, BP, HRV, biochem markers

External Load Monitoring

key performance indicators (KPI)

Acceleration

rate of change of velocity

- Object accelerates when it speeds up, slows down, starts, stops, & changes direction

- Instantaneous versus average acceleration

Acceleration equation

a=vf-vi/t

Vf

final velocity

Vi

initial velocity

t

time

Is Acceleration directional?

No, only + or -

- Instantaneous versus average acceleration

Explain Pelvic Acceleration with a progression that increases with difficulty

The more difficult the progression, the greater the pelvic ACC

Projectile Examples

Human body and objects

Uniform Acceleration: Projectiles

- constant net external force acting on an object with vertical motion being constant

- an object that has no external forces acting on it other than gravity

- Vertical motion is a constant: g = -9.81 m/s^2

Law of Inertia

horizontal velocity component is constant

Vertical Velocity

will change from + at release, to 0 peak, and - upon return

Vpeak

0 m/s

Horizontal Acceleration

0 m/s^2

Vertical Acceleration

-9.81 m/s^2

Projectile Calculations

Vertical position

Vertical velocity

Horizontal velocity

Horizontal position

Vertical & horizontal displacement

Flight time

Vf = Vi + gΔt

Solve for projectile’s final velocity

- a = Vf – Vi / Δt will also be = g

- Vf – Vi = g Δt

1st Law of Uniformly Accelerated Motion

A projectile's final velocity is related to its Initial velocity & constant acceleration

Vf^2 = Vi^2 + 2gΔy

If vertical displacement is known

3rd Law of Uniformly Accelerated Motion

A projectile's final velocity is related to its acceleration & displacement

Vf = (g)(Δt)

or

Vf^2 = 2g(Δy)

If an object is free falling (Vi = 0m/s)

Vi^2 = 2g(Δy)

if an object is thrown up (Vf = 0 m/s)

2nd Law of Uniformly Accelerated Motion

A projectile's final position is related to its initial velocity & acceleration

yf = yi + (vi)iΔt - (1/2)g(Δt^2)

solving for vertical position