Page 73 - Mechanical Engineer's Data Handbook

62 MECHANICAL ENGINEER'S DATA HANDBOOK

h2 + kZ
-=L'= the length of the equivalent simple pendulum.
h
(Also equal to the distance to the centre of percussion)
Where: k = radius of gyration about CG, h = distance from pivot to CG.

2. I. 15 Gravitation
This deals with the mutual attraction which exists 6.67 x 5.97
between bodies. The magnitude of the force depends F= 6.37' x 10m2=9.81m2=gm2
on the masses and the distance between them. For two
masses m, and m, a distance d apart, the force is: Thus: g=9.81 ms-'
F=G- m1m2 Variation of g with height and latitude
d2
If
where: G is the 'gravitational constant'
=6.67x 10-'1Nm2kg-2 L = degrees latitude (0' at equator)
h = height above sea level (km)
For a body m, on the earth's surface
m, = 5.97 x loz4 kg (earth's mass), d=6.37 x lo6 m g = 9.806294 - 0.025862 COS 2L + O.ooOO58 COS' 2L - 0.003086h
(earth's radius). Then

2. I. I6 The solar system

The following table gives useful information on the sun, moon and earth.

Earth Sun Moon

Mass (kg) 5.97 x 1024 2 1030 7.34 x 1022
Radius (km) Equatorial 6378 696000 1738
Polar 6357
Average density (kgm-3) 5500 1375 3300
Period of revolution
About axis 23 h 56min 25 days 27.33 days
orbital 365.26 days 27.33 days
Acceleration due to gravity (ms-') 9.81 2.75 x 10" 1.64
Mean orbital radius (km) 149.6 x lo6 - 384 400
Miscellaneous information Tilt of polar Type G star. Period between
axis 23f" Absolute magnitude 5.0. new moons=
Surface temperature 29; days
6ooo"C.
Centre temperature
14 x 106'C