Page 253 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

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Measurement of absolute initial velocity of V, distance method free makes measure- essentially suspended station spring

235 velocity of V, at (z). acceleration (T). fall.

Gravity Weight drop. The object an 0), to a falls a Pendulum. Gravitational function of the pendulum’s Jength of oscillation drop in to: that one the on

of 8.14 accelerates from = (T 1), as it = (L) and period weight object an according observations gravity object an from exerts
Measurement FIGURE gravily.a) time at (T time b) is a the In gravity. for measured ms oscillates gravity Relative ( gravimeter) of mass taken is gravimeter mass (m)

Perndulum absolute are accordiag to: dot? + Vot g=2(z—v,t)/? perzdulum a VL/g 2a pendulum according to: L(4zx°/T’) absolute reliable, consuming. time instrument an The 8.15a). the the that (F) (g): acceleration F= mg

b) measure displacement = 2 falls z distance object the 8.14b), = T the pendulum. = g obtain and easily, with (L::Fig. When force the

to and computed object the of gravity. thus: (Fig. of computed to expensive done spring constant. gravitational
ways is the fall velocity is method of swing of the is be a of remains however,

= V; basic velocity the gravity distance to time initial absolute gravity period length gravity necessary length another, local
Drop V saee Gravity two are 8.14a), absolute = z t = Vo = = g absolute second the = T _L = absolute Gravity precision measurements however, can the spring the to with the

Weight frnenemreld.. Absolute There (Fig. The where: The Using where: “ The Relative The those ments, measures from location varies

T=0 Te
a)

rela- object gravita- (g). acceleration to
and an in a) Absolute gravity is acceleration (g,) compared
absolute of Relative gravity reflects the gravitational station
+2.67) —1.64) in acceleration difference 8.13 truc gravitational in one

= = the FIGURE difference another (g,).
p (for (7Ga/) p (for (77Gal) (m). (17Gal) measured is the b) (Ag) at

(m). BC 0.0419ph anomaly (m). datum h, | sea al point TC + anomaly cas be can the actual] gravity another.
datum — Ag, — Ag, (mGal) (g/cm?) mGal/m)h | mGal/m) anomaly observation Agy = gravity (71Gal). surface reflects relative to

(Gal) (Gal) Jevel = (0.112 gravity sea-level below Agne Earth’s gravity while compared
Isostasy gravity sea Ag, correction density — Bouguer above (0.0687 gravity depth Bouguer correction GRAVITY on surface, station

and gravity above Gravity Anomaly Bouguer reduction Ag, elevation Ag, + Bouguer Terrain: complete Absolute Earth’s one
Gravity observed theoretical elevation = = Land = Ag, simple = = Sea = I = water h,, = Rugged = = terrain OF acceleration 8.13). at

= = = BC p On Ag, h b) At Ag,, Ag,, In Ags, TC (Fig. toward acceleration Gravity Gravity
g g, h Bouguer a) c)
Chapter 8 MEASUREMENT Gravitational senses tive falls it as tional G9

234 Absolute Relative
a) b) g