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For use with Chapter 8
Universal Gravitation

Earth on a Diet?
Posted May 15, 2000

New evidence has come to light that Earth has lost weight - or, to be more accurate, it has "lost" mass. However, Earth didn't actually lose any mass. Using new measurement techniques, scientists have determined that the mass of our planet is actually less than originally thought.

On Saturday, April 29, 2000, at a meeting of the American Physical Society, the revised mass was announced. Previously, it was calculated that Earth had a mass of 5.978 x 10e21 metric tons. Now, by using a more precise method of measuring, scientists have determined that Earth has a mass of 5.972 x 10e21 metric tons. While this is only a difference of about one-tenth of one percent, it means that the calculation was off by about 6 sextillion metric tons.

This recalculation was sparked by a recalculation of the gravitational constant G. A physicist at the University of Washington did this by making improvements to Cavendish’s experiment that was used to calculate G in the 18th century.

If this new value is universally accepted by the scientific community, it would have an impact on the accuracy of current calculations of the magnitude of the force of gravity. Still, the data is preliminary and subject to change upon further experimentation. It will help reduce the uncertainty by a factor of 100. But before this value is accepted by the International Committee for Data for Science and Technology, the research must be reviewed and duplicated.

Activity
Use the Internet sites given here to learn how the gravitational constant is determined. Write an article in your Science Journal explaining why it is inaccurate to say that the weight of the Earth has changed.

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