Biomedical Engineering Reference
In-Depth Information
Table of Example 3.5
Coordinates of C.G.
Parts of body
x
(cm)
y
(cm)
Mass (kg)
Head
10.0
77.5
4.8
Neck-trunk-crossed arms
10.0
36.0
41.1
Thigh (both)
19.0
10.0
15.0
Leg (both)
60.0
10.0
6.7
Feet (both)
88.0
10.0
2.4
(a) Find the coordinates
x
A
and
y
A
of the C.G. of the set head-neck-trunk-
crossed arms.
(b) Locate the coordinates
x
B
and
y
B
of the C.G. of the set thigh-legs-feet.
(c) Calculate the coordinates
x
C.G.
and
y
C.G.
of C.G. of this person's body and
explain why we do not feel comfortable in this posture.
(a) It is not necessary to find the coordinate
x
A
, since all the segments are aligned at
10.0 cm. Then, we have only to find the coordinate
y
A
:
ð
77
5cm
Þ
ð
4
8kg
Þþ
ð
36
0cm
Þ
ð
41
1kg
Þ
:
:
:
:
y
A
¼
¼
40
:
3cm,
45
:
9kg
x
A
¼
10.0 cm.
(b) In this case, we do not have to calculate the coordinate
y
B
which is equal to
10.0 cm for all segments. Let us find, then, the coordinate
x
B
:
ð
19
0cm
Þ
ð
15
0kg
Þþ
ð
60
0cm
Þ
ð
6
7kg
Þþ
ð
88
0cm
Þ
ð
2
4kg
Þ
:
:
:
:
:
:
x
B
¼
¼
37
3cm,
:
24
1kg
:
10.0 cm.
(c) Now we have to find both coordinates, from the answers obtained in (a) and (b):
y
B
¼
ð
10
0cm
Þ
ð
45
9kg
Þþ
ð
37
3cm
Þ
ð
24
1kg
Þ
:
:
:
:
x
C
:
G
:
¼
¼
19
:
4cm,
70
0kg
:
ð
40
3cm
Þ
ð
45
9kg
Þþ
ð
10
0cm
Þ
ð
24
1kg
Þ
:
:
:
:
y
C
:
G
:
¼
¼
29
:
9cm
:
70
0kg
:
Based on the last results, that is,
x
C.G.
and
y
C.G.
, taking into account the four
factors related with body stability, we can analyze the reason for the discomfort in
this posture:
1. The height of the C.G. of the body in this posture is reasonably low, giving good
equilibrium.
2. The size of the support base is large, providing good equilibrium.
