Replies to This Discussion

Permalink Reply by George on July 10, 2011 at 8:39am

"but this might be a good place to explain how the universe is expanding and even our milky way galaxy is not fixed in the universe."

Also note that galaxies occur in clusters, which don't necessarily expand. Instead they tend to orbit each other, collide, etc.

Permalink Reply by ROMAN ROMACH on July 9, 2011 at 12:38pm

There is no up and down in space.  The people on the opposite side of the earth see up and down differently from you.  So up and down depends on where a person is on the earth. Imagine that everything in space is like dust floating in air -but there is no up or down, so there is nowhere to fall.

 

The earth spins very fast, but we don't fall off because the earth's gravity pulls on us and keeps us in place.  When something falls, it is just gravity pulling it.  The earth revolves around the sun - like a stone on a string - because the gravity of the sun keeps it from shooting off into space.  If the string breaks, the stone will fly away.

 

The sun cannot fall, unless a larger sun comes close to it and pulls it with its own, greater gravity.  The earth cannot fall toward the sun because we are moving too fast - like the rock on a string.

 

Hope this helps.

 

 

 

    

Permalink Reply by George on July 24, 2011 at 8:53am

Another useful image:

 

 

From the wiki page "Orbit". This demonstrates the two primary forces at work in maintaining a stable orbital motion.

Attachments:

• Orbital_motion.gif, 135 KB

Permalink Reply by Bwambale Robert on July 24, 2011 at 11:56am

George,

Thanks for that informative illustrative answer.

Permalink Reply by Bwambale Robert on August 11, 2011 at 1:35pm

Thanks Caroline for the elaboration.

Permalink Reply by George on August 11, 2011 at 2:20pm

Caroline, Robert:  A nebula is a cloud of dust and gas in interstellar space; galaxies aren't part of nebulas.  Often are created by exploding stars.  

 

Example: This is the Crab nebula, which is the remains of a star that exploded several thousand years ago.

Permalink Reply by Chris Thompson on August 16, 2011 at 6:55pm

All the bodies in the solar system are actually moving around their center of mass, which is quite close to the sun (sun is so heavy.) Here's sun's orbit: http://www.orbitsimulator.com/BA/sbc4.GIF

Permalink Reply by Ava Wilson on August 22, 2011 at 7:36pm

It's not in a fixed position. It's constantly moving. Everything is just so far apart, they don't touch. Plus the 'force' of gravity. Gravity is what's holding everything "in place", or rather, everything's moving, but they're moving together because of the force of gravity between them.

Permalink Reply by Jim Christensen on August 22, 2011 at 9:17pm

I think kids would understand an analogy the best.  The one l like to use is to put a ball on a string and swing it around your head.  The string will be taut as it rotates your head.  At that time, there is a balance of forces.  The string (gravity) keeps the ball from going outward, but the velocity of the ball (or the planet) keeps it from coming inward.  If the ball were to slow down, it would rotate closer to the body, and that happens when satellites slow down and crash into earth.  There are other principles that can be demonstrated, but it would depend on how well the kids understand the first demonstration.

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