W9 Centre of Gravity & Stability

Question 1

What is Newton’s Law of Gravity?

Answer 1

• If two bodies attract one another with a force that is directionally proportionate to the masses of them both as well as the distance between them.
• Meaning if two objects are further away they will have less attraction also if they have greater masses they will be more attracted.
• Normally with humans & sport it is negligible

Question 2

A diver and a sky diver both jump. Who would be subject to more gravitational attraction and why?

Answer 2

• The diver would be subject to more gravitational attraction because they’re closer to the earths core.
• However, the difference between the sky diver & the diver is negligible as the distance to the centre of the earth is ~>6,400,000. So the difference between 3m & 3,000m is negligible

Question 3

Where is earth slightly flatter?
Where does the earth bulge slightly?
Does it make a difference if athletes train at the poles or the equator?

Answer 3

• The earth is slightly flatter at each pole
• The earth bulges slightly at the equator
• Yes, at the equator athletes are ~21km from the earths core which is a lot less negligible
• So events such as shot put & long jump would benefit if they are closer to the equator because there is less gravitational pull

Question 4

What is Resultant force?

Answer 4

• The attraction of all given particles of the object

Question 5

Every particle that makes up the body experiences an attraction towards Earth.
True or False?

Answer 5

True

Question 6

What is the Line of Gravity?

Answer 6

• It is the vertical line through the point at which the object would balance

Question 7

If we rotate an object will the Line of Gravity change on the object or remain the same?

Answer 7

• It will change on the object because it must always be vertical

Question 8

What is the Centre of Gravity?

Answer 8

• The point about which gravitational force is balanced
• The Centre of Gravity is where the horizontal and vertical Lines of Gravity will intersect
• Centre of gravity moves if the orientation of body segments change (so if you bend over your centre of gravity changes)

Question 9

Can you name the three things that change the Centre of Gravity?

Answer 9

1. Shape of Boyd/object
2. Position of limbs
3. Distribution of mass

Question 10

Can you describe how the Centre of Gravity acts during flight?

Answer 10

• The Centre of Gravity acts like a partial during flight

- This means the flight path cannot be changed by body movements during flight

Question 11

What are the three methods used to determine Centre of Gravity?

Answer 11

1. Balance Method (E.g. balancing a ruler on your finger)
2. Suspension (E.g. using a weight on the end of a string)
3. Reaction Board (Layer down on a board)

Question 12

What is stability?

Answer 12

• “resistance to linear and angular acceleration” or resistance to change

Question 13

What are the three factors that influence stability of a body during equilibrium?

Answer 13

1. Position of the line of gravity relative to the limits of the base (having a wide stance), Greater distance = more stable
2. Height of the centre of gravity from the base, Lower centre of gravity = more stable
3. Weight of the body, Greater weight = more stable

Question 14

Stability & Line of Gravity:
In sporting context if the line of gravity moves outside its base the body will tend to rotate. This could be looked at as being unstable.
- Would this create a negative or positive effect on sporting performance?

Answer 14

• It could create both (depending on the sport/situation)
  Positive = A swimmer about to dive into the water. Having the line of gravity close to the edge will allow for a quick equilibrium change at “Go”
  Negative = If you need to keep your balance in surfing, snowboarding and/or gymnastics and loose your balance this would negatively effect your performance.