Monday, May 7, 2018

WATER ON THE EARTH - How much water is there on Earth? - There's a whole lot of water on Earth! Something like 326,000,000,000,000,000,000 gallons (326 million trillion gallons) of the stuff (roughly 1,260,000,000,000,000,000,000 liters) can be found on our planet. This water is in a constant cycle -- it evaporates from the ocean, travels through the air, rains down on the land and then flows back to the ocean. The oceans are huge. About 70 percent of the planet is covered in ocean, and the average depth of the ocean is several thousand feet (about 1,000 meters).

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Water On The Earth
How much water is there on Earth?
There's a whole lot of water on Earth!
Something like 326,000,000,000,000,000,000 gallons (326 million trillion gallons) of the stuff (roughly 1,260,000,000,000,000,000,000 liters) can be found on our planet.
This water is in a constant cycle -- it evaporates from the ocean, travels through the air, rains down on the land and then flows back to the ocean.
The oceans are huge. About 70 percent of the planet is covered in ocean, and the average depth of the ocean is several thousand feet (about 1,000 meters).
Ninety-eight percent of the water on the planet is in the oceans, and therefore is unusable for drinking because of the salt.
About 2 percent of the planet's water is fresh, but 1.6 percent of the planet's water is locked up in the polar ice caps and glaciers.
Another 0.36 percent is found underground in aquifers and wells.
Only about 0.036 percent of the planet's total water supply is found in lakes and rivers.
That's still thousands of trillions of gallons, but it's a very small amount compared to all the water available.
The rest of the water on the planet is either floating in the air as clouds and water vapor, or is locked up in plants and animals (your body is 65 percent water, so if you weigh 100 pounds, 65 pounds of you is water!).
There's also all the soda pop, milk and orange juice you see at the store and in your refrigerator …
There's probably several billion gallons of water sitting on a shelf at any one time!
It would be more proper to ask, "What is the mass of planet Earth?" 
The quick answer to that is approximately 6,000,000, 000,000,000,000,000,000 (6 x 1024) kilograms.
The interesting sub-question is, "How did anyone figure that out?"
It's not like the planet steps onto the scale each morning before it takes a shower.
The measurement of the planet's weight is derived from the gravitational attraction that the Earth has for objects near it.
It turns out that any two masses have a gravitational attraction for one another.
If you put two bowling balls near each other, they will attract one another gravitationally.
The attraction is extremely slight, but if your instruments are sensitive enough you can measure the gravitational attraction that two bowling balls have on one another.
From that measurement, you could determine the mass of the two objects.
The same is true for two golf balls, but the attraction is even slighter because the amount of gravitational force depends on mass of the objects.
Newton showed that, for spherical objects, you can make the simplifying assumption that all of the object's mass is concentrated at the center of the sphere.
The following equation expresses the gravitational attraction that two spherical objects have on one another:
F = G(M1*M2/R2)
  • F is the force of attraction between them.
  • G is a constant that is 6.67259 x 10-11 m3/kg s2.
  • M1 and M2 are the two masses that are attracting each other.
  • R is the distance separating the two objects.
Assume that Earth is one of the masses (M1) and a 1-kg sphere is the other (M2).
The force between them is 9.8 kg*m/s2 -- we can calculate this force by dropping the 1-kg sphere and measuring the acceleration that the Earth's gravitational field applies to it (9.8 m/s2).
The radius of the Earth is 6,400,000 meters (6,999,125 yards).
If you plug all of these values in and solve for M1, you find that the mass of the Earth is 6,000,000,000, 000,000,000,000,000 kilograms (6 x 1024kilograms, or 1.3 x 1025 pounds).
It is "more proper" to ask about mass rather than weight because weight is a force that requires a gravitational field to determine.
You can take a bowling ball and weigh it on the Earth and on the moon.
The weight on the moon will be one-sixth that on the Earth, but the amount of mass is the same in both places.
To weigh the Earth, we would need to know in which object's gravitational field we want to calculate the weight.
The mass of the Earth, on the other hand, is a constant.
 
 

 

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