Ch9: The Science of Biomechanics

biomechanics

study of internal and external forces acting on the human body and effects

quantitative analysis

• research based

• based on quantity

qualitative analysis

information that can be readily obtain to asses performance

kinematics

describes spatial and timing characteristics of motion of the human body without reference to the forces that cause the motion eg time, distance, velocity, acceleration

kinetics

• describes forces leading to motion

• they can be internal or external

internal forces

happens inside the body

external forces

acts outside the body

mass

the amount of matter in an object

inertia

the reluctance to change motion unless by an external force

moment of inertia

• the more the mass the more the inertia

• movement of inertia is rotation

gravity

force of attraction between 2 bodies

difference between mass and weight

• mass is the measure of inertia

• weight is the measure of the force of gravity

types of motion

• linear motion/translation

• angular motion/rotation

• general motions

linear motion/translation

all body parts move in a straight line

angular motion/rotation

moves on circular parts in the same direction

general motions

combination of linear and angular

force

any action that causes an object to change its course of motion

causes of linear motion

forces that act through a bodies force of mass

torque (moment of force)

when a force causes angular motion

components of lever system

• axis of rotation

• fulcrum (pivot)

• lever attached to fulcrum

types of levers

• first class

• second class

• third class

first class levers

applied force and resistance are located on opposite sides eg crowbar, seesaw, neck region

second class lever

force and resistance are on the same side

• force acts far away from axis (fulcrum)

eg wheelbarrow

third class lever

• force and resistance on the same side

• applied force closer to the axis

• human body consists of mainly third class levers, due to this we are at a biological disadvantage

• make humans faster

newtons 1st law

law of inertia: objects will not change state of motion unless acted upon by an external unbalanced force

newtons 2nd law

law of acceleration: objects experience change in velocity proportional to the external unbalanced force

newtons 3rd law

law of action-reaction: for every action there is an equal and opposite reaction

fluid environments

• water

• air

• water + air

drag

type of fluid force that acts opposite to the bodys direction and works to slow you down

profile drag

caused by an objects size and shape

surface drag

caused by an objects roughness

the faster you go-

the more drag you experience

body size and surface roughness

surface drag

boundary layer

a thin layer of fluid that is carried with the body

laminar flow

very little disruption, the air around you moves smoothly

turbulent flow

disruption in the air flow

profile drag

resistive drag against an object and it is characterized by turbulent flow

profile drag reducing strategies

• decrease frontal surface area

• decrease source of turbulence

drafting

taking advantage of the region of air shielded by another athletes body

magnus force

net difference in pressure on opposite sides of a rotating object

topspin

downwards magnus force

• boundary layer flows opposite to relative airflow

• air is slowed by friction

• zone of increased pressure created

backspin

upwards magnus force

• boundary layer flow same as relative airflow

• air is not slowed down

• zone of decreased pressure created

equilibrium

not experiencing change in direction of speed

static equilibrium

no movement

dynamic equilibrium

movement at a constant speed

balance

ability to maintain equilibrium

balance is affected by two factors

1. base of support: larger your base of support the better your balance

2. location of line of gravity: best at the centre of your base of support

stability

measurement of how hard it is to disrupt your equilibrium

increase in stability: static equilibrium

• increase in base size

• increase in body size

• lower centre of gravity

• increase distance between gravity line intersecting base and outside base

increase in stability: dynamic equilibrium

• widen base

• move centre of gravity towards the edge

• shift centre of gravity towards oncoming force

• use reflex to regain loss of balance