Centre of mass

Question 1

What is the definition of centre of mass?

Answer 1

The point about which the mass of the body is equally distributed

Question 2

What is the definition of the balance point?

Answer 2

If a body is suspended at this point it has no tendency to rotate

Question 3

What is another name for the balance point?

Answer 3

Centre of gravity

Question 4

When using BSIP tables, what point of trunk and head are treated as proximal ends?

Answer 4

Shoulder

Top of head

Question 5

What theory does the direct method of locating COM use?

How is this applied

Answer 5

Principle of moments

Moments about fulcrum sum to zero

Question 6

What is the formula used to calculate location of COM in the direct method?

Answer 6

F(r).L=w.x

Where

F(r) = reaction force measured by scales

L = distance of scales from fulcrum

w = weight of individual/body

x = distance of COM from fulcrum

Question 7

Explain in words the principle which is used to determine the COM in the indirect (segmentation) method

Answer 7

Sum of moments of individual segments about x and y axes is equal to the whole body moment

Question 8

What formula is used to determine the whole body COM in the indirect (segmentation method)?

Answer 8

Whole body COM (x-axis).Whole body mass

Sum(segment COM (x-axis).segment mass)

Question 9

What are the 3 methods which have been used for deriving (BSUP) body segment standard parameters?

Answer 9

1. Cadaver studies
2. Mathematical geometric models - representing body segments as regular geometric solids
3. Medical imaging techniques
   i. computer tomography (CT scan)
   ii. Magnetic resonance imaging (MRI)

Question 10

What are the limitations of deriving BSIPs from cadaver studies?

Answer 10

1. Density differs from living tissue
2. Very small sample sizes
3. Samples not representative of average adult population (for race, age, height, weight, sex , body composition etc)

Question 11

What are the key aspects re how the Dempster study was carried out?

What year was this?

Answer 11

• 1955
• 8 Caucasian males (52-83 years old, 49-72kg)
• segmental COM found with balance plate method
• segmental volumes found with immersion method
• moments of intertia fond with free swinging pendulum

Question 12

What are the key aspects re how the Clauser study was carried out?

What year was this?

Answer 12

• 1969
• 13 Caucasian males
• 49 +/- 14 years old
  67+/-9kg
• regression equations used to estimate segmental mass, centre of mass, volume

Question 13

What are the key aspects of the Chandler study?

Wat year was this carried out?

Answer 13

(1975) studied six male cadavers (54±7 yrs; mass 65±13 kg). Segmental mass, volume, COM location and the principal mass moments of inertia of each segment were determined