> "Why is everything 17,500, how do they get this speed"
This is the orbital speed for orbits near the surface of the earth ("near" = 200 to 300 miles altitude, more or less). This speed is based on (1) the strength of gravity near the earth's surface (it's roughly the same at the surface as it is at 300 miles altitude), and (2) the curvature of the earth's surface. No matter what horizontal speed you have, gravity will curve your path toward the earth. But the amount of curvature depends on how fast you're going. If you go slower than 17,500 mph, the curvature of your path is sharper than the the curvature of the earth's surface, which means you will draw closer to the earth. If you go faster than 17,500 mph, the curvature of your path is shallower than the earth's curvature, and you will pull away from the earh's surface. If you go at just the right speed (around 17,500 mph), the curvature of your path will just match the curvature of the earh's surface, and you will maintain a constant distance from it.
At higher altitudes, the "perfect speed" is smaller, because the strength of gravity is less out there. For example, GPS satellites orbit at an altitude of absolute 12,000 miles; and at that altitude, the "perfect" speed is about 8,700 mph, so that's the speed at which they go.
> "how do they stay at this speed?"
Rockets insert the satellites at just the right speed for their particular altitude. Once they're in motion, their momentum keeps them moving (see Newton's First Law of Motion). In the absence of any retarding force (such as air resistance), an object will maintain its speed indefinitely.
> "Why [do] an astronaut and his spacecraft stay close together at such high speeds?"
The astronaut maintains his sideways momentum as he steps outside for EVA. Since their is no resisting force to slow him down, he continues along at his initial speed, namely the same speed as the spacecraft.
This is the orbital speed for orbits near the surface of the earth ("near" = 200 to 300 miles altitude, more or less). This speed is based on (1) the strength of gravity near the earth's surface (it's roughly the same at the surface as it is at 300 miles altitude), and (2) the curvature of the earth's surface. No matter what horizontal speed you have, gravity will curve your path toward the earth. But the amount of curvature depends on how fast you're going. If you go slower than 17,500 mph, the curvature of your path is sharper than the the curvature of the earth's surface, which means you will draw closer to the earth. If you go faster than 17,500 mph, the curvature of your path is shallower than the earth's curvature, and you will pull away from the earh's surface. If you go at just the right speed (around 17,500 mph), the curvature of your path will just match the curvature of the earh's surface, and you will maintain a constant distance from it.
At higher altitudes, the "perfect speed" is smaller, because the strength of gravity is less out there. For example, GPS satellites orbit at an altitude of absolute 12,000 miles; and at that altitude, the "perfect" speed is about 8,700 mph, so that's the speed at which they go.
> "how do they stay at this speed?"
Rockets insert the satellites at just the right speed for their particular altitude. Once they're in motion, their momentum keeps them moving (see Newton's First Law of Motion). In the absence of any retarding force (such as air resistance), an object will maintain its speed indefinitely.
> "Why [do] an astronaut and his spacecraft stay close together at such high speeds?"
The astronaut maintains his sideways momentum as he steps outside for EVA. Since their is no resisting force to slow him down, he continues along at his initial speed, namely the same speed as the spacecraft.
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