the answer files

Why is the sky blue?

What is lightning?

What are the states of matter?

Does hot water freeze faster than cold?

Why does a can of Coke sink while a can of Diet Coke floats?

Why do you close your eyes when you sneeze?

Why do mosquitoes bite me more than my friends?

Why do your feet stink?

How does gravity work?

How fast does the space shuttle move in orbit?

What is escape velocity?

What would happen if you turned on your headlights while moving at the speed of light?

How fast does the space shuttle move in orbit?
shuttle Answer: faster than a speeding bullet -- 7,757 meters per second, or 17,532 miles per hour.

Space shuttle courtesy of NASA.

Objects must obey Isaac Newton's first law: Objects in motion tend to remain in motion unless they're acted upon by a force. For orbiting objects, that force is gravity.

In other words, satellites "want" to continue moving in a straight line, and if gravity suddenly disappeared, they would move away at a tangent to the circular orbit. Similarly, if you swing a rock on a sling and release it, the stone will not move directly away from you. Rather, it departs tangentially.

Enough David and Goliath stories. The Why Files asked Tom Intrator, who teaches dynamics and orbital mechanics at the University of Wisconsin-Madison, to tell us how fast the shuttle moves. We started with the simplifying assumption that the shuttle follows a circular path (it doesn't, but lies can be helpful).

Intrator told us that the shuttle's speed reflects only these factors:

gravitational constantEarth's mass ("M")

The shuttle's radius ("r") from the Earth's center of mass and

The gravitational constant ("G"),

Kg = kilograms

M = meters

S = second

orbital velocityHere's how they are related:

The equation shows that orbital velocity varies with the distance between the shuttle and Earth's center, and that a satellite further from Earth has a slower orbital velocity than one close in. That makes sense, since gravity decreases with distance, so less velocity is needed to overcome gravity in a larger orbit.

G may look ugly, but it's handy, since it works everywhere. Thus Luke Skywalker could have used G to calculate orbital velocity around the Death Star (assuming he could find the mass of the star).

If the shuttle accelerated much faster, it would be traveling at escape velocity.

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The Why Files
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