No one really knows what creates the force of gravity. These effects are of minor importance when measuring mass. If your object is located in a valley, there will be an attraction upward toward the peak of nearby mountains, and in fact there will also be a gravitational attraction sideways toward the mountain. The acceleration of gravity has been measured with an accuracy of better than 1 part in 10 million at many locations on earth. There is a special science known as gravimetry which investigates variations in local gravity. Although the average of the vector forces to each particle is approximately equal to a vector to the mass center of the earth, there will be some variation due to the concentration of dense materials in the earth’s crust at certain locations. Those particles that are close to the object exert the strongest influence, since the force is inversely proportional to the square of the distance. An object on the surface is attracted to every small particle in the earth. The earth is not a perfect sphere, nor is its density uniform, so that there is a variation in attraction due to the irregularities of the surface and the non-uniform density.

Therefore, it is necessary to correct for the change in the acceleration of gravity between the site where the scale was calibrated, and the site where the object is being measured.īrowse Center of Gravity Measurement Tools 1.2 Gravity Discussionįor two spheres of uniform density, the force of attraction is proportional to the square of the distance between the center of the spheres, as shown in figure 1. For large scale capacities, it is often not possible to bring a calibration weight to the new site, either because this weight is not available, or because of the problems of shipping a calibration mass weighing many thousands of pounds. The standard weight is the weight the mass would have at standard gravity of 32.17405 ft/sec2 (9.80665 m/sec2).Ī problem occurs when a load cell type scale is calibrated at one location and then moved to another location to weigh an object. The scale is then adjusted until it reads the appropriate standard weight. To calibrate a scale, a standard calibration mass is placed on the scale. This process is often called “calibrating the scale”. In order to measure mass, some method must be used to compensate for the acceleration of gravity at the particular location in which a spring or load cell scale is used. If scales are used in commerce, an inspector will test them not for their accuracy in measuring force, but rather for their accuracy in measuring mass. Otherwise, you could buy the ounce of gold in Miami and sell it in Boston at a profit. An ounce of gold must “weigh”one ounce in Miami or Boston. An object should “weigh” the same, no matter what scale it is weighed on, or where the scale is located. In fact, most accurate scales measure mass. There is a common misconception that scales measure weight. 1.0 Variations in the acceleration of gravity Standard acceleration of gravity

Since then there has been a lot more work on the subject to define the gravitational acceleration. He is supposed to have dropped a large and a small object from the leaning tower of Pisa and found that they both hit the ground at the same time. This is the method made famous by Galileo. Gravitational acceleration can be measured by dropping an object in a vacuum chamber and measuring speed as a function of time as the object accelerates.

Gravity acceleration