MadSci Network: Astronomy

Re: Earth's and Moon's Gravity

Area: Astronomy
Posted By: Mark Friedman, Undergrad, Biology
Date: Thu Dec 12 12:23:20 1996

That is a very interesting question that you asked. The moon is 238,857 miles from the Earth. Its diameter 2,160 miles. Both the rotation of the Moon and its revolution around Earth takes 27 days, 7 hours, and 43 minutes. This unique synchronous rotation is caused by an unsymmetrical distribution of mass in the Moon, which has allowed Earth's gravity to keep one lunar hemisphere permanently turned toward Earth.

As the Apollo 11 astronauts found out on June 20, 1969 the moon's gravity is one-sixth that of the Earth's. Therefore, a person who weighs 180 pounds on Earth weighs only 30 pounds on the Moon. However, as you could imagine, their muscle strength remains the same. This is why films of the Apollo lunar missions reveal the astronauts jumping high into the air (really vacuum).

Because the Moon has neither an atmosphere nor any water, the components in the soils do not weather chemically as they would on Earth. Simply put, erosion does not occur, so that rocks more than 4 billion years old still exist, yielding information about the early history of the solar system that is unavailable on Earth

Now to your question about escape velocity. The surface gravity on the earth if 9.78 m/sec^2. With this in mind, the equatorial escape velocity in 11.18 km/sec. This means that in order to escape the earth's gravitational field, a spacecraft must be moving at that speed.

I hope this helps.

Check out this site for some great information on our solar system.

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