January 12, 2006 Net Report

A total of 20 Amateur Radio Operators checked in to tonight's net. Thanks to all!

Trivia Question:

How much would you weigh at the center of the earth?

A) Nothing
B) The same as you do at the surface of the earth
C) An infinate number of pounds

Trivia Answer:

A) Nothing!

A good way to see this is to imagine yourself falling through Earth. Suppose there is a perfectly smooth well that goes straight through Earth and out the other side. It's airless so there's no air friction to hold you back — and forget about the huge temperatures and pressures down deep. This is a thought experiment. You take an impossibly deep breath, step over the edge, and fall into the well.

As you step off, all of Earth is below you and that entire mass pulls your mass and you start to fall. As you fall, though, now some of Earth is above you and there is, consequently, less Earth below you. The farther you fall, the less of Earth there is below pulling you down and the more Earth mass there is above pulling up. So you get lighter as you fall.

Finally, (about 21 minutes later) when you reach the center of Earth, you weigh nothing at all because half of Earth is above you and half below. The two pulls cancel.

By the way, you're going your fastest now as you whiz towards the opposite end of Earth at a blazing 17,700 mph (28440 km/h). In another 21 minutes you'll pop out of the well somewhere in the middle of the Indian Ocean. Then — back you go towards Kansas or wherever you started from.

"You'll continue to bob back and forth through the center of the Earth with your head popping out at your starting point every 84.5 minutes," says Rod Nave, physics professor at Georgia State University. "It's amusing that this is about the same time it takes a satellite to orbit Earth (right above the surface)."

Further Reading:

HyperPhysics by Rod Nave: Hole through Earth

HyperPhysics by Rod Nave: Earth's gravity

From USA Today “Wonderquest” By April Holliday

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Here's the stations that checked in to the net tonight. A * indicates that they got the trivia question answer correct. Thanks to all.

• WB6ATV Ron *
• KE6CZH Robert *
• KG6DBL Bill
• K6FCC Khalil *
• KE6IYC Brian *
• KD6JEV John
• N6KAS Andy
  
• KG6KTC Leon
• K6LMN Roger *
• W6NVY Gary
• K6MSU Ron
• K6QVZ Joe *
• KG6RDA Sidney *
• KF6RMC Michael
• KG6TRR Bob
• KF6ZQM Harry
• N6ZZK Ted
• K6LCS Clint *
• KC2CYL Anthony *