Earth is the densest planet in the solar system and weighs roughly 5.972 × 10^24 kg. Like its density, which increases towards the core, Earth's mass is not evenly distributed. Earth is so big that is cannot be measured on a scale. Therefore, scientists use mathematics and the law of gravity to estimate the weight of Earth. This weight fluctuates depending on gases and dust escaping the atmosphere, as well as other activities in the solar system activities, such as meteors and comets hitting Earth.
How Is the Weight of Earth Calculated?
In order to calculate the weight of Earth or any other planet, the gravitational effect has to be considered. It is not possible to measure the weight of Earth on a scale, as you would measure the weight of smaller objects. To determine the weight of Earth, the relative gravitational force acting upon Earth has to be determined. It is also necessary to consider the sun’s gravitational field. Since the radius of Earth is known, it becomes easier to determine its weight. The law of Universal Gravitational Force is used to calculate the mass of Earth, whereas its radius is used to calculate the distance.
History of Studying the Weight of Earth
Efforts to determine the weight of planet Earth began as early as the 18th century. Henry Cavendish was the first scientist to attempt to determine the weight of Earth in 1798. Cavendish invented an apparatus to help him determine the weight of Earth, which was a dumbbell-like instrument that had two-inch spheres made of lead stuck to a six foot rod. A wire was tied around the center of the rod to ensure the rod was suspended and free for movement. A dumbbell larger in size was kept near the first dumbbell.
The second dumbbell was twice as large as the first, and they were placed near each other so that the larger bell would attract the smaller one. This attraction would exert a small torque on the suspended rods, and as the rods oscillated Cavendish would record the movements. He attempted to minimize any possible distracters, such as air movements. Cavendish continued observing the oscillations until he was satisfied that the oscillations could be used to determine the gravitational force of the big and small spheres.
Since the density of the spheres was known, the ratio of the two forces could be used determine Earth’s density, which is equal to its volume divided by its mass. The mass of Earth is roughly 5.972 × 10^24 kg. The results of Cavendish's study were accurate compared to the results of other recent findings.
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