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MichelleW
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| Posted: March 14 2007 at 9:23pm | IP Logged
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We have been studying magnetism (I am so awful at this). The kids figured out that magnets only stick to things that have iron in them. This morning ds asked me if gravity was like a big magnet. I stupidly said, "yes!" without really understanding what he was asking or knowing how to answer him. He asked, "If gravity is like a big magnet, how come things that don't have iron in them don't fly off the earth?"
Help!
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Michelle
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lapazfarm
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| Posted: March 15 2007 at 10:18am | IP Logged
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Good question! People have been trying to understand gravity for ages, and it still isn't exactly understood.
Think of it in this simple way...Gravity is a property of all matter (unlike magnetism, which is a property of only certain types of matter). Everything has it, even you and me! The bigger you are (the more mass you have)the more gravity you have. We exert a gravitational pull ourselves, but since the earth is so much bigger, it's pull is MUCH stronger than ours and in effect, drowns ours out. That is why we stick to the earth. The sun is bigger yet, which is why the earth is stuck in orbit around the sun, and so on.
Does that help?
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Theresa
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MacBeth
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| Posted: March 15 2007 at 12:20pm | IP Logged
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Also, Michelle, I think you might be picturing the gravitational field like the magnetic field in text book pictures of a giant bar magnet through the earth, with a north and south pole. Gravity is a different force; it is fairly uniformly strong across the whole planet, and it is not polar at all. It holds the oceans as well as the atmosphere. And the earth is big...really big. 
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MacBeth in NY
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MichelleW
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| Posted: March 15 2007 at 4:04pm | IP Logged
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Ok, thanks. I was thinking this last night, that it had something to do with matter, but I was having trouble reconciling this with magnetism.
So, basically gravity is like a magnet in the figurative sense (I am more of a poet than a scientist). This phrase works as a simile to help us understand that gravity attracts and magnets attract, but beyond that the similarity is tenuous. Gravity is NOT a magnet. It is a pull based on matter, and the more dense the object the greater the pull.
Did I get it? And we don't know why matter has gravity?
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Michelle
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lapazfarm
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| Posted: March 15 2007 at 4:13pm | IP Logged
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Not necessarily the more dense, but just the greater amount of matter (mass), regardless of the volume it occupies.
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Theresa
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MacBeth
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| Posted: March 15 2007 at 4:14pm | IP Logged
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I think you've got it, Michelle.
An excellent treatment of gravity and all can be found in Faraday's Forces of Matter. I know it looks like a grim little book, but it is actually a series of lectures meant for school children, and it's really well-written and understandable...and charming!
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MacBeth in NY
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MacBeth
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| Posted: March 15 2007 at 4:15pm | IP Logged
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lapazfarm wrote:
| Not necessarily the more dense, but just the greater amount of matter (mass), regardless of the volume it occupies. |
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Good point. Saturn is less dense than earth, but it has a stronger gravitational attraction.
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MacBeth in NY
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4Real Forums : Exploring God's Creation in Nature and Science
Topic: Why don't we just fly off the earth?
