centre of mass

Question 1

centre of mass

Answer 1

point at which a body is balanced in all directions and from which weight/ gravity appears to act

Question 2

where is the centre of mass in the human body

Answer 2

about the belly button

Question 3

is the centre of mass always in the same position

Answer 3

• it isn’t a fixed point
• it alters as a person changed their body position

Question 4

what happens when both arms are raised up to COM

Answer 4

it is raised

Question 5

what happens to COM when someone bends forwards

Answer 5

it moves forwards and down

Question 6

what is the location of the centre of mass dependent on

Answer 6

the distribution of body mass

Question 7

why is centre of mass manipulated

Answer 7

to improve technique by altering body position

Question 8

what is the COM of a symmetrical object e.g football

Answer 8

it’s actual centre

Question 9

where can the centre of mass move to

Answer 9

the outside of a body

Question 10

where is the centre of mass of any object

Answer 10

where the mass of the object is concentrated

Question 11

is the centre of mass a fixed point

Answer 11

• no, it is moveable

Question 12

as the body moves what happens to COM

Answer 12

it moves

Question 13

stability

Answer 13

• the ability to resist motion and remain at rest
• to withstand force and return to its original position

Question 14

which 2 ways is centre of mass position important

Answer 14

• balance
• rotation

Question 15

what is COM dependent on

Answer 15

• COM: height of the centre of mass
• Base of support: number of bases of support
• Line of gravity: position of the line of gravity
• Mass : mass of the body

Question 16

how stable is a sumo squat wrestler ?

Answer 16

• COM: height has decreased, increasing stability
• BOS: 2 bases, increasing stability and a wider stance
• LOG: is further within the BOS increasing stability and shorter to ground
• Mass: increased stability as sumo wrestler has greater body mass

Question 17

the lower the centre of mass the what

Answer 17

more stable the performer

Question 18

why does a gymnast flex the hip and knee after a vault landing

Answer 18

• COM: lower
• LOG: shorter - widening base of support
• LOG further within BOS
• providing a more stable landing

Question 19

why do judo performers have a wide stance

Answer 19

• COM: lower / shortened LOG
• BOS wider so LOG further within BOS so position is more stable
• increasing the difficulty to be thrown

Question 20

the greater the size of base of support the greater the what

Answer 20

stability

Question 21

why is the bridge a stable balance

Answer 21

• BOS is increased in size by having 4 contact points
• COM is lower to the ground and BOS is further within BOS / LOG is shorter
• increasing stability of the balance

Question 22

line of gravity

Answer 22

an imaginary line extending from the COM to the ground

Question 23

an object will stay stable as long as the line of gravity from the COM stays within what

Answer 23

base of support

Question 24

the more central the line of gravity is to the base of support the what

Answer 24

greater the stability

Question 25

mass of the body

Answer 25

greater the mass of a body the greater it’s inertia and greater it’s stability

Question 26

why does the rugby prop have good stability

Answer 26

- increased body mass increased stability due to an increased equal and opposite reaction force - enables them to withstand a force - decreased height: lower COM and shorter LOG

Question 27

if the Log is outside the BOS the body will be what

Answer 27

unstable

Question 28

eccentric force

Answer 28

- the line of gravity moves outside of the base of support - the force of gravity and mass of the body act upon the COM - causing the body to become unstable and topple over

Question 29

how do we make COM more stable

Answer 29

- make it low / short log

Question 30

how can we make BOS more stable

Answer 30

increase contact points of bases of support

Question 31

how can we make line of gravity more stable

Answer 31

- is further within the base of support = more stable

Question 32

how does mass increase stability

Answer 32

bigger mass = more stable

Question 33

how is a sprinter stable in the crouched position in the blocks

Answer 33

- low COM as she’s in a crouch - more points of base of support x5 = more stable - line of gravity is further within base of support - sprinter has a higher muscle mass = greater reaction force

Question 34

how does the sprinter minimize stability when the gun is fired

Answer 34

- chest is lifted raising COM - hands leave the track reducing the points of contact and bases of support - line of gravity moves forwards outside the base of support resulting in body falling forwards

Question 35

as the LOG has moved outside the base of support what does the sprinter need to do

Answer 35

- drive one leg forward with great speed - movement time is minimized giving a perfect start to the race

Question 36

how can a high jumper manipulate the body shape and location of COM to maximize performance

Answer 36

- uses ‘J curve’ to allow a greater velocity in this approach - plants the outside foot allowing the inside leg to lift with the arms at take off raising the COM as high as possible - back is in hyper extension - weight of legs and head are below the hips - this makes the COM move below the body - Fosbury flop is in a more efficient position as COM travels under the bar while the jumper clears the bar - only 1 part of the body has to be above the bar at any one time