stability and balance “define and apply the principle of balance to a selected sport in relation...
TRANSCRIPT
STABILITY AND BALANCESTABILITY AND BALANCE
• “Define and apply the principle of balance to a selected sport in relation to:– The centre of gravity i.e. Line of gravity, width of base of support, height of
centre of gravity– Static balance– Dynamic balance
• “Define and apply the principle of balance to a selected sport in relation to:– The centre of gravity i.e. Line of gravity, width of base of support, height of
centre of gravity– Static balance– Dynamic balance
www.flickr.com/photos/keithallison/4062226811/
1©PE STUDIES REVISION SEMINARSHome
Curriculum Council of Western Australia. Physical Education Studies Support Document 2009.
BALANCEBALANCE
• BALANCE: The ability to neutralise forces that disturb equilibrium.– Standing on one leg– Scooping a ball up on the run– “Bouncing” off a tackler without falling
2©PE STUDIES REVISION SEMINARSHome
STABILITYSTABILITY
• Object’s resistance to movement, from a balanced position. There are two types of stability:
1. STATIC STABILITY— when an object is at rest and not moving with linear or angular motion.
2. DYNAMIC STABILITY— when an object is in motion and moving with linear or angular motion.
www.flickr.com/photos/lcrward/2662994322/
3©PE STUDIES REVISION SEMINARSHome
CENTRE OF GRAVITYCENTRE OF GRAVITY
•The point around which a body’s weight is equally balanced in all directions• Also referred to as the center of mass (need not be physically located inside of a body)•Standing still – centre of gravity is located in the abdominal cavity, about 6 inches above the pubis symphysis.•As your position changes – so does your centre of gravity.•The position of the centre of gravity will determine whether the body is in balance.
COG
4©PE STUDIES REVISION SEMINARSHome
DETERMINING THE CENTRE OF GRAVITYDETERMINING THE CENTRE OF GRAVITY
• To determine ones COG, simply draw a box around the objects outer extremities
• Then draw diagonal lines through the box, with the point of intersection determining the objects approximate COG.
• To determine ones COG, simply draw a box around the objects outer extremities
• Then draw diagonal lines through the box, with the point of intersection determining the objects approximate COG.
www.flickr.com/photos/dearlydeparted/3834132754/
5©PE STUDIES REVISION SEMINARS
Home
Approximate COG
• In sports like High Jump and Pole Vault, where athletes are trying to attain maximum height, individuals will endeavour to position their COG outside of their body, having it pass beneath the bar whilst their body passes above it, to help achieve maximum height.– They achieve this by arching their back (hyperextension)
• In sports like High Jump and Pole Vault, where athletes are trying to attain maximum height, individuals will endeavour to position their COG outside of their body, having it pass beneath the bar whilst their body passes above it, to help achieve maximum height.– They achieve this by arching their back (hyperextension)
©PE STUDIES REVISION SEMINARS6
CENTRE OF GRAVITY AND SPORTCENTRE OF GRAVITY AND SPORT
www.flickr.com/photos/philmcelhinney/452585754/
Home
COG passes through or beneath the bar whilst the athlete passes over the bar
COG passes through or beneath the bar whilst the athlete passes over the bar
BASE OF SUPPORTBASE OF SUPPORT
What is the base of support?
Area bound by the outermost regions of contact between a body and support surface
7©PE STUDIES REVISION SEMINARS
Home
1. MASS OF THE OBJECT• The greater the mass of an object, the greater its stability will be, given
that all other factors are equal.
1. MASS OF THE OBJECT• The greater the mass of an object, the greater its stability will be, given
that all other factors are equal.
FACTORS AFFECTING BALANCE & STABILITYFACTORS AFFECTING BALANCE & STABILITY
Sumo wrestlers have excellent stability as a
result of their increased mass
Sumo wrestlers have excellent stability as a
result of their increased mass
www.flickr.com/photos/wilhelmja/378453316/ 8©PE STUDIES REVISION SEMINARS
Home
2. SIZE OF THE OBJECTS BASE OF SUPPORT• The greater the area of support, the greater the degree of stability.
2. SIZE OF THE OBJECTS BASE OF SUPPORT• The greater the area of support, the greater the degree of stability.
FACTORS AFFECTING BALANCE & STABILITYFACTORS AFFECTING BALANCE & STABILITY
9©PE STUDIES REVISION SEMINARSHome
FACTORS AFFECTING BALANCE & STABILITYFACTORS AFFECTING BALANCE & STABILITY
Low COG = ↑ stability
High COG = ↓ stability
10©PE STUDIES REVISION SEMINARS
Home
3. THE HEIGHT OF THE COG ABOVE THE BASE OF SUPPORT• The line of gravity or pull of gravity will always pass vertically through
the centre of an object’s mass. • The higher the centre of gravity above the base of support, the less
stable the object is. Athletes often lower their centre of gravity by bending the knees in order to increase their stability
3. THE HEIGHT OF THE COG ABOVE THE BASE OF SUPPORT• The line of gravity or pull of gravity will always pass vertically through
the centre of an object’s mass. • The higher the centre of gravity above the base of support, the less
stable the object is. Athletes often lower their centre of gravity by bending the knees in order to increase their stability
4. THE POSITION OF THE LINE OF GRAVITY RELATIVE TO THE BASE OF SUPPORT
• The line of gravity is an imaginary vertical line passing downwards through the centre of gravity. The closer the line of gravity is to the limits of the base of support, the less the degree of stability of the object.
• Movement is easier when the line of gravity falls outside the object’s base of support
4. THE POSITION OF THE LINE OF GRAVITY RELATIVE TO THE BASE OF SUPPORT
• The line of gravity is an imaginary vertical line passing downwards through the centre of gravity. The closer the line of gravity is to the limits of the base of support, the less the degree of stability of the object.
• Movement is easier when the line of gravity falls outside the object’s base of support
FACTORS AFFECTING BALANCE & STABILITYFACTORS AFFECTING BALANCE & STABILITY
↑ Stability as line of gravity located well
within base of support
↑ Stability as line of gravity located well
within base of support
11©PE STUDIES REVISION SEMINARSHome
5. INCREASING THE SIZE OF THE BASE OF SUPPORT IN THE DIRECTION OF THE ONCOMING FORCE
5. INCREASING THE SIZE OF THE BASE OF SUPPORT IN THE DIRECTION OF THE ONCOMING FORCE
FACTORS AFFECTING BALANCE & STABILITYFACTORS AFFECTING BALANCE & STABILITY
Oncoming force
12©PE STUDIES REVISION SEMINARS
Home
6. HORIZONTALLY POSITIONING THE COG NEAR THE EDGE OF THE BASE OF SUPPORT ON THE SIDE OF THE EXTERNAL FORCE
6. HORIZONTALLY POSITIONING THE COG NEAR THE EDGE OF THE BASE OF SUPPORT ON THE SIDE OF THE EXTERNAL FORCE
FACTORS AFFECTING BALANCE & STABILITYFACTORS AFFECTING BALANCE & STABILITY
Oncoming force
13©PE STUDIES REVISION SEMINARS
Home
More stable Less stable
Low COG Higher COGWide base of support – 4 point contact Small base of support – 2 point contactLine of gravity in middle of support Similar line of gravity
Low COG Higher COGWide base of support – 4 point contact Small base of support – 2 point contactLine of gravity in middle of support Similar line of gravity
STABILITY VARIES WITH BODY POSITIONSTABILITY VARIES WITH BODY POSITION
14©PE STUDIES REVISION SEMINARS
Home
Centre of Gravity, Stability & BalanceCentre of Gravity, Stability & Balance
• In many sports skills, players are required to unbalance quickly in order to have a fast movement time. This can be done by either;– Decreasing the size of the effective base and/or– Displacing the centre of weight quickly outside the effective base (move the
line of gravity close to the base of support)
Line of gravity passes close to edge of base of support, reducing stability allowing the runner to get out of the blocks faster
Line of gravity passes close to edge of base of support, reducing stability allowing the runner to get out of the blocks faster
15©PE STUDIES REVISION SEMINARS
Home
• E.g. When receiving service a tennis player has to be prepared to move quickly in a sideways direction. In order to respond to a wide serve the player sways form side to side keeping the centre of weight in motion across the base of support. With the centre of weight in motion, less effort is required to unbalance the player when the decision to move in a particular direction is made. At the last moment players will also be seen to bring their feet closer together thereby decreasing the size of the effective base and facilitating an unbalancing effect.
COG, STABILITY AND BALANCECOG, STABILITY AND BALANCE
www.flickr.com/photos/stuseeger/2419626533/www.flickr.com/photos/15740359@N06/2736645585/
16©PE STUDIES REVISION SEMINARS
Home
Sports Requiring Low StabilitySports Requiring Low Stability• Sprint starts – swimming and
athletics• Tennis – service reception• Any aspect of sport requiring
quick lateral movement or change of direction
• Sprint starts – swimming and athletics
• Tennis – service reception• Any aspect of sport requiring
quick lateral movement or change of direction
Sports Requiring High StabilitySports Requiring High Stability• Wrestling• Weight lifting• Collision sports
• Wrestling• Weight lifting• Collision sports
17©PE STUDIES REVISION SEMINARSHome
COG, STABILITY AND BALANCECOG, STABILITY AND BALANCE