Will it Float?

My 7 year old rubber band ball

After two weeks of what turned out to be some seriously one sided wagering, it was time for the test. But first let's review the scene for those of you whom have either been missing for awhile, or have just surfed here on accident.   For close to 7 years now, I've been saving up the rubber bands that the USPS wraps around my mail. And while I'm not exactly sure why it started, I do know that after the first week or two of receiving them, I started to make a ball.

After awhile, the thing started to grow rather large and is now sort of a visitor highlight to anybody who comes to my office. Pretty interesting to be sure... but would it float?

The Stats The ball is 5 inches in diameter     It weighs 2 1/4 pounds at 55% humidity     it is totally comprised of the 3 types of USPS   issued rubber bands     When dropped from a height of 3 feet, the ball   bounces to a height of 20 inches (55.5% return)   The Scene To make sure the environment was a "clean" one, and to appease rv.com staff member wmartin, we used a room temperature version of Memphis' purified Artesian well water for the experiment. Ava even measured the water temperature ahead of time with this nifty thermometer that hankword gave me for my birthday.   So with the scene set, we cleared the area, started the video and started taking pictures.

3...2...1... TEST!

With the video rolling and Ava standing close by, very close by, we released the ball into the water. Click here for a WMV video account of the results. I think you will find it worth the download.

The Verdict Definitively, it can be said that a ball made of 7 years worth of USPS rubber bands will sink. No doubt about it. In fact, it sinks so bad that the conditions set forth in the wager ahead of time were not even testable. (3 minutes and keep a lego man dry)   Furthermore, it should also be noted that if for some reason you decide to attempt or re-create this test on your own, keep any small children in desperate need of a nap clear of the testing area. The resulting splash from this type of test can apparently be upsetting.

Final Analysis Since this was what we would call an unexpected result (14 float to only 1 sink votes were cast), I decided to do a little "why" processing. So I marked the water line, removed and drained the rubber band ball, and then proceeded to re-fill the bucket up with 4 3/4 ounces of water. Therefore, given that volume, and a weight of 2 1/4 lbs, should the ball have floated? Somebody do the math for me. I'm just "the idea guy" around here.   Thanks for participating, and come back soon for more fascinating wagers. As for those of you who participated, your RVPR has been adjusted.

rvining - 12/8/2007 5:37:08 PM the results are IN! did it float? come check it out, and be sure to watch the video.

kgarrett - 12/8/2007 9:50:35 PM darn, I missed that one badly. Still well worth 10 points to get video evidence of you terrorizing your kid.

kristen - 12/8/2007 11:17:09 PM I love Ava

aj - 12/9/2007 1:19:55 PM it sunk, sank, and is sinking...bummer for me!

kristen - 12/9/2007 4:09:20 PM Congratulations William and Ashley on taking the plunge like this rubber band ball!

rvining - 12/10/2007 1:42:54 PM didn't the rubber band ball sink? is this a good analogy?

kgarrett - 12/10/2007 8:29:33 PM The rubber band ball also proved us all wrong- which I think makes it an appropriate analogy. Just kidding, congrats!

rvining - 12/11/2007 12:33:23 PM where exactly did we all go wrong on this. who's good at 'new math' around here. we have weight, volume, etc all out there. somebody D=MVT pie R cube this thing with a calculator.

danb1155 - 12/11/2007 2:04:17 PM Can you fill up your kitchen sink and try it again. I don't think that you had enough water

rvining - 12/11/2007 9:38:26 PM let's wait till spring and throw it into the pool. WLM wants to wrap it in foil to keep it water tight and try it again as well.

robthompson - 12/13/2007 6:45:28 AM Not enough water = false negative. I contend that no object will float in a body of water comprised of less mass than the object itself.

aj - 12/13/2007 10:47:46 AM good point, rob

rvining - 12/14/2007 8:45:12 AM whoa whoa whoa. let me get this straight. so like a battleship wouldn't float at horseshoe? displacement is like a law or something. has nothing to do with how much water is IN the lake. william needs to get in here and settle this. he is the staff mathematician. what he says goes (unless i disagree)

wmartin - 12/14/2007 9:17:16 AM My opinion: If the rubber band ball was solid and had the same density characteristics if would float as it initially did. The problem is that the ball is porous. As time elapsed water permeated the ball so the amount of water displaced decreased and it sank. Wrap it in Seran Wrap and I wager 20 it floats if water tight.

kgarrett - 12/14/2007 3:18:33 PM Density of water at 70.9 degrees (21.61 degree Celsius) = 0.99786 g/cm^3 Volume of ball= (4/3) * Pi *(6.35)^3 = 1072.53083 cubic centimeters Mass of water displaced: =1072.53083cm^3 * 0.99786 g/cm^3 =1070.23561 grams Therefore the ball displaces 49.65278 grams (or 4.6%) more water than it weighs and therefore should float. However, this is assuming an ideal pure experiment and math. Several confounders exist: First of all, the calculations above used the density of pure water but, because of fluoride etc, tap water is likely slightly more dense than pure water. The nearest reference for density of tap water was at 20 degrees Celsius, where tap water is 0.00003grams per cubic cm denser than pure water, adjusting the calculations for this would only add 0.0032grams, which is clearly negligible. More concerning is the inexact measurements of the ball used in the calculations (I doubt it is precisely 2.25 lbs and exactly 5 inches in diameter). I am not maligning RVs measurement skills but with such a close margin (4.6%), a little fudging on either measurement could be significant. Plus, the ball is not a perfect sphere which affects the calculations. Williams argument is very valid too; if the ball is porous enough to absorb any water it could easily overcome the slight mathematical tendency to float. Therefore I think the mathematical result is officially too close to call (i.e. Vegas would set the line as a pick-em). PS. Yes, I know that I am a geek.

kgarrett - 12/14/2007 3:23:06 PM Sorry, cut and paste difficulties. The complete comment shoud have begun All right, Im stuck by myself in a hotel and bored, so I worked out the math, here goes. Diameter 5 inches, so radius = 2.5 inches = 6.35 cm Weight 2.25 lbs = 1020.58283 grams Density of water at 70.9 degrees (21.61 degree Celsius) = 0.99786 g/cm^3 Volume of ball= (4/3) * Pi *(6.35)^3 = 1072.53083 cubic centimeters Mass of water displaced: =1072.53083cm^3 * 0.99786 g/cm^3 =1070.23561 grams

ava - 12/14/2007 5:03:04 PM the ball fell in and I got all wet. can I have a peanut butter and jelly circle now?

aj - 12/15/2007 5:05:01 PM huh? kgarrett, that sounds like a good argument to me. i want a redo!

rvining - 12/16/2007 2:27:14 PM no No NO! there are no 'do-overs' in FEPO. just for the sake of argument however, I will be wraping the ball up in some Reynolds Plastic Wrap to make it airtight (per wlm's suggestion), but that is it. the thing SANK. it is time for the next wager.