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Why Doesn't the Earth Get Pulled into the Sun by Its Gravity?

Classified by scientists as a yellow dwarf, the Sun is a medium-sized (approx. 870,000 miles in diameter) star composed of mostly hydrogen and helium. Holding nearly 99.9% of all mass in the entire solar system, the Sun is not only responsible for sustaining all life on Earth, but it's also necessary for the formation of the solar system itself. All the planets revolve around the Sun in regular elliptical orbits at various speeds, and each requires a specific length of time to complete one full revolution.

Distance
- The closer you are to a large object, the stronger you feel its gravitation force. For example, on Earth we feel a gravitational pull of 1G, which equals to an accelerative force of 9.8 meters per second, each second. Because of this gravitational attraction, a skydiver jumping out of an airplane is able to quickly reach about 125mph, or what is referred to as "terminal velocity." At this point the air resistance acting on the skydiver's body will not allow him to go any faster. However, in a vacuum, any body subjected to a gravitation force could in theory keep accelerating indefinitely.
Speed
- One way of overcoming the pull of gravity is to build up enough speed. This method is exactly how astronauts aboard the Space Shuttle are able to go on missions to the International Space Station. The large rocket engines develop several million pounds of thrust, which propels the shuttle at high velocity on its way to achieving a stable earth orbit. The shuttle orbits Earth at 18,000 miles per hour, or approximately 6 miles per second -- which is exactly Earth's escape velocity -- or the speed required to break free of the Earth's gravitation pull.
The Sun's Gravity
- Scientists have calculated the Sun's gravity to be 28 times higher than that of Earth. If a 150-lbs. human were able to walk on the surface of the Sun, she would weigh 4,200 lbs., or about as much as a full-size sport utility vehicle. It is this large mass and gravitational force that acts on all of the other planets in the solar system -- and keeps them from flying off into space -- while the Sun remains at the center.
Orbiting a Star
- Even at an average distance of 94 million miles, the Earth must still travel 18.75 miles each second to maintain the delicate balance and stay in orbit. If the Earth were to suddenly speed up, the Sun's gravitation field would no longer be strong enough to keep it in orbit, and the Earth would leave the solar system. Conversely, if Earth were to slow along its orbital path, it would be pulled closer and closer into the Sun. Velocity is key in overcoming the force of gravity and maintaining a stable orbit.

Astronomy