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 tia Joined: Mar 2001 Posts: 8,807 Blog Entries: 6 Senior Member
tia

Joined: Mar 2001
Posts: 8,807
Senior Member
density!
12-03-2007, 06:46 PM
 #4

get an aquarium and fill it with water--get a variety of balls, including tennis ball, wiffle ball with holes, golf ball, and marble....(thank, PE teacher!) and have kids guess what will happen--some sink, some float and some sink a little) you can talk about why

then have a coke and diet coke--point out that each can contains the same amount (ugh! i can't think of the flippin word for it--but its the measurement word --oh! capacity!) the coke will sink and the diet coke will float halfway. then discuss how even though they have the same size can and same capacity (amount inside), the weight is different. (i don't really know why...i guess the sugar in the coke weighs more than the sweetener in diet coke?)

give everyone one of those fat short Silo cups--2/3 full of water--give them a "fun size" snickers and a (crud! i can never remember which one it is--either milky way or 3 musketeers....i think it's 3M....i always have to check each year!) have them unwrap them (actually, do this in partners or groups so you don't waste as much candy!) then have them measure the length, width, height (round) and then find the volume. so they see that each candy bar takes up the same amount of space. drop in the snix and it sinks. drop in the 3M and it floats! oh, yah, it's the 3M, cause it has that fluffy inside. anyway, then you can discuss the fact that the snickers is denser---even though it's the same size, it's heavier. density is the ratio of weight compared to volume. (so it's not just the weight--you can't compare a giant rock to a little rock) and it's not just the size. (actually, i think i do the candy bit before the coke bit....)

i've always wanted to paint a styrofoam brink to look like a real brick and then have them guess what will happen when dropped in tank---so they see that same size, different density.

i ask them: what weighs more a pound of feathers or a pound of sand? (duh--they are both a pound) BUT: what is denser, a cup of feathers or a cup of sand?