Staging – Why?
•Why do modern rockets have multiple launch stages that separate instead of just one stage?
•Answer: To increase the thrust to weight ratio. Thereby increasing the rate of acceleration, and therefore lowering the overall weight and size of the original rocket.
•If the Apollo-Saturn V rocket did not have all the separate stages, it would have been close to 2 or 3 times as tall and massive and harder to control.
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http://vintagespace.files.wordpress.com/2011/04/saturn-v-cutaway.jpg
Stage Weights (wet):

1st(Bottom): 5,100,000 (wet) or 289,000 (dry)

2nd:  1,060,000 (wet) or 80,000 (dry)

3rd:   262,000 (wet) or 23,000 (dry)