surveying iii (topographic and geodetic surveys) - Modern Prepper

of a horizontal rod with a small sphere of equal mass at each end. The dumbbell-shaped rod wassuspended at the center by a sensitive twistable fiber. Large lead spheres of known mass were placed atthe ends of the rod, near the small spheres, in such a way that the gravitational pull between the smalland large masses caused the rod to rotate horizontally. Knowing the weights, the distances of themasses, and the torsion of the twisted fiber, Cavendish computed the value of G to be 6.754 x 10 -8 or,written out, 0.00000006754 centimeter-gram-second (cgs) units. This constant is the force in dynes thatis exerted between two masses of 1 gram each with centers 1 centimeter apart. Cavendish's value is veryclose to the latest accepted value of 6.673 x 10 -8 cgs units determined in 1942 by Dr. Paul R. Heyl at theNational Bureau of Standards. Dr. Heyl used a refined version of Cavendish's device.d. Using the following formula we can determine the acceleration (a) of mass m2 due to theattraction of mass ml by dividing F, the force of attraction, by mass m2. (In Newton's second law ofmotion, force is the product of mass times acceleration). Any force acting on a unit mass createsacceleration, which gives a measure of the gravitational attraction at any point on the earth's surface.e. The pull of gravity is usually expressed in terms of the acceleration of a freely falling body,expressed as the rate of increase of velocity per unit of time. A G-force of one is the force required toaccelerate any freely movable body at the rate of about 32.16 feet per second per second. A G metermeasures the G force in aircraft. A G is equal to approximately one thousand gals, a unit of gravitymeasurement named after Galileo. The gal has an acceleration of one centimeter per second per second(1 cm/sec2). The acceleration of gravity over the earth's surface ranges from approximately 983 cm/sec2or 983 gals at the poles to 978 cm/sec2 or 978 gals at the equator. Theoretically, if you were to jumpfrom an airplane above the equator, you would fall faster and faster, gaining speed at the rate of 978 gals(about 32 feet) every second. At the end of two seconds, you would be falling at the rate ofapproximately 1,956 centimeters (about 65 feet) per second. After each succeeding second, the speedincreases at a rate of 978 gals per second.f. A smaller unit of measurement used in gravity measurements is the milligal, or one-thousandthpart of a gal. It is used when dealing with variations in acceleration equal to one-millionth of one G.Modern instruments go even beyond this, measuring acceleration changes of one-billionth of a G or toone-thousandth part of a milligal.g. Gravity can be defined as the attraction that the earth has for every particle on its surface. Theforce of gravity holds all objects on the earth in place and prevents them from flying off into space as theearth rotates. Gravity is what brings back to the ground a golf ball hit into the air and makes water flowdownhill. It is because of gravity that all things on earth possess weight. An average person will weighabout 1 pound more at the poles where the attraction is greater than he will weigh at the equator wherethe attraction is weaker. The variation of the earth's gravity, with respect to latitude, is caused by twofactors--the rotation of the earth and the earth's ellipsoidal shape. TheEN0593 1-18