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 02-22-2010, 10:11 PM #1 happy_terd Banned   Posts: 13,046 Karma: 10105011 Join Date: Jan 2010 Location: Finally made it to Walmart. Device: PRS 420 density Egg project with my 8 year old daughter complete. We put in enough salt into a glass of water to make an egg float to the top of the cup. The reason behind the egg floating is an easy one. An egg has a higher density than regular water so it sinks. An egg has a lower density than salt water so it floats. "Density (ISO 31: volumic mass) is a measure of mass per unit of volume." http://wikinfo.org/index.php/Density ------------------- My daughter did the work herself and understands everything but the definition of density and I am at a loss to put it in a way that an 3rd grader would understand. Anyone got a good way of describing density to help me help her understand it?
 02-22-2010, 10:33 PM #2 pholy Booklegger     Posts: 1,800 Karma: 7999034 Join Date: Jun 2009 Location: Toronto, Ontario, Canada Device: BeBook(1 & 2010), PEZ, PRS-505, Kobo BT, PRS-T1, Playbook, Kobo Touch Density is weight divided by volume, or weight per unit of volume. How about comparing a steel ball and a cork ball the same size? The steel ball weighs more - it has more weight for the same size chunk. I don't know if that works - my daughter is now teaching high school physics (too far away to ask), so I haven't had to explain this stuff for a long time. But keep at it, 'cause physics is half of how the world works - the other half is psychology (I think). Good luck!
 02-22-2010, 10:39 PM #3 nikkie Guru     Posts: 607 Karma: 73700 Join Date: Oct 2009 Location: Redmond, WA Device: iPhone, iRex DR800SG, Pocket Edge, iPad Haha, now you just need to explain saturation and buffers and start making acids of various strengths... Sorry, I loved the solutions portion of chemistry! I wish I had learned why you can only put so much salt or sugar in a solution before it starts to precipitate much earlier.
02-22-2010, 10:40 PM   #4
happy_terd
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Quote:
 Originally Posted by pholy Good luck!
thanks. This is difficult getting her to understand. So far the best kid friendly definition I found was:

"It is, essentially, a measuremement of how tightly matter is crammed together."

02-22-2010, 10:43 PM   #5
nikkie
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Quote:
 Originally Posted by happy_terd thanks. This is difficult getting her to understand. So far the best kid friendly definition I found was: "It is, essentially, a measuremement of how tightly matter is crammed together." http://physics.about.com/od/fluidmec.../f/density.htm
Yeah, I think the real problem is that you have to have a good solid understanding of mass before you can really grok density. And understanding mass means taking it back to atomic mass and the periodic table. And that would take a while.

 02-22-2010, 11:08 PM #6 kindlekitten Professional Adventuress     Posts: 13,362 Karma: 50260224 Join Date: Sep 2009 Location: The Olympic Peninsula on the OTHER Washington! (the big green clean one on the west coast!) Device: Kindle, the original! Times Two! and gifting an International Kindle easy explanations... first make jello and have her stick her finger in it... explain as she meets the resistance about the resistance being dense. next, (and this is a really cool/fun one!) make crystals... take sugar or salt (I don't have the correct proportions, that could probably be googled). make the mixture, put it into a glass, take a pencil, tie a string, (and this has to be a good old fahioned cotton string as it needs to "wick") around it, and let it drape into the water. the water will evaporate and the sugar or salt will form crystals around the string. this should help explain it! (it is REALLY cool to put food coloring in the water!) edit: the pencil lays atop the glass with the string dangling down
02-22-2010, 11:30 PM   #7
happy_terd
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Quote:
 Originally Posted by kindlekitten easy explanations... first make jello and have her stick her finger in it... explain as she meets the resistance about the resistance being dense. next, (and this is a really cool/fun one!) make crystals... take sugar or salt (I don't have the correct proportions, that could probably be googled). make the mixture, put it into a glass, take a pencil, tie a string, (and this has to be a good old fahioned cotton string as it needs to "wick") around it, and let it drape into the water. the water will evaporate and the sugar or salt will form crystals around the string. this should help explain it! (it is REALLY cool to put food coloring in the water!) edit: the pencil lays atop the glass with the string dangling down

That actually sounds kind of fun.

 02-23-2010, 12:05 AM #8 kindlekitten Professional Adventuress     Posts: 13,362 Karma: 50260224 Join Date: Sep 2009 Location: The Olympic Peninsula on the OTHER Washington! (the big green clean one on the west coast!) Device: Kindle, the original! Times Two! and gifting an International Kindle it is! I did stuff like this with both my kids and my Girl Scouts whenever possible. Scouting has had a HUGE push to turn girls on to the maths and sciences, and that came out of a "fun science" dealio
 02-23-2010, 04:25 AM #9 Katti's Cat Wizard     Posts: 2,261 Karma: 175640 Join Date: Nov 2009 Location: Brisbane Australia Device: Sony PRS-600 Water & oil are good examples too. Take equal parts, lets say 1/4 cup. Let her stick her finger in both to 'feel the density', which is the resistant the fluid makes around the finger. Then put them together in a jar, close lid tight, shake and see how they separate.
 02-23-2010, 10:34 AM #10 cmdahler Addict   Posts: 292 Karma: 24688 Join Date: Aug 2009 Device: Sony PRS-505, iPad I think the best way to describe density to a 3rd grader is the statement someone else posted earlier: it's just how tight you've got matter crammed together. You can give her a better visual of density by showing her how light and powdery a pile of flour is, and then adding a little water and kneading it into a tight ball to show how you've increased the density of the flour by just compacting it into a much smaller volume.
 02-23-2010, 10:41 AM #11 GeoffC Chocolate Grasshopper ...     Posts: 27,163 Karma: 19597778 Join Date: Mar 2008 Location: Scotland Device: Cybook Gen3 , Pocketbook 302 (Black) , Nexus 10: wife has PW ...and then you have to explain why ice, which is very hard, is able to float on water; seemingly a paradox when considered to some of the other excellent examples above.
 02-23-2010, 11:02 AM #12 cmdahler Addict   Posts: 292 Karma: 24688 Join Date: Aug 2009 Device: Sony PRS-505, iPad Yes, I'd stay away from that one, unless you're really into making Lego models of atoms in a crystalline structure! I haven't had that question pop up, but I did recently have to try to explain why the sky is blue to a fourth grader, and that took a bit of doing. Mostly she got bored halfway through and ran off.
02-23-2010, 11:03 AM   #13
GeoffC
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Quote:
 Originally Posted by cmdahler Yes, I'd stay away from that one, unless you're really into making Lego models of atoms in a crystalline structure! I haven't had that question pop up, but I did recently have to try to explain why the sky is blue to a fourth grader, and that took a bit of doing. Mostly she got bored halfway through and ran off.

i can sympathise ....

02-23-2010, 11:07 AM   #14
dsvick
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Quote:
 Originally Posted by cmdahler I think the best way to describe density to a 3rd grader is the statement someone else posted earlier: it's just how tight you've got matter crammed together. You can give her a better visual of density by showing her how light and powdery a pile of flour is, and then adding a little water and kneading it into a tight ball to show how you've increased the density of the flour by just compacting it into a much smaller volume.
Unless you used self-rising flour, in which case you had better talk fast.

02-23-2010, 11:10 AM   #15
dsvick
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Quote:
 Originally Posted by cmdahler Mostly she got bored halfway through and ran off.
Better than her eyes glassing over and fainting. My daughter just calls my wife when I try to explain something like that, usually something like .... "Mom!! Dad's doing it again."

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