# Floating Lemons and Sinking Limes

## Why do lemons float in water but limes don't?

Scientists seem to be infatuated with objects that float and sink. Even non-scientists find great joy in dropping stuff in water to see if it floats or sinks. Fans of David Letterman are quick to point out one of Dave's favorite segments called, "Will It Float?" Here's the latest float or sink challenge: Why do lemons float in water but limes sink? Think you know the answer? Not so fast...

### Materials

• A few lemons and limes that are roughly the same size and weight. A big lemon and a tiny lime will throw off your test results.
• A deep container like a large bowl
1. Fill a bowl with water and drop in the lemons. Float or sink? They should float.
2. Toss the limes into the water. Float or sink? You might get a few that float but just barely. The limes in our test sank to the bottom.
3. Now it's time to figure out why. Your first guess might be the rinds of both fruits. Peel the rind off of the lemon and you'll find that it is thick and porous, similar to the rind of an orange (that also floats in water). The lime rind is much thinner than the lemon and does not contain the same porous material.
4. It's time to test the peeled lemon and lime. Drop both in the water and you might be surprised. The lemon floats and the lime sinks! So, it's not the rind.
5. That's as far as we're going to take you. Keep experimenting and exploring before reading any further.

### How does it work?

At first, our team of lemon lime researchers were certain that it had everything to do with the rind because of their experience with floating and sinking oranges. Drop an orange into water and it floats, but remove the peel from that same orange and it will sink. The unpeeled orange floats because the rind is very porous and filled with tiny pockets of air. Even though you're removing mass when you peel the orange, the peeled orange is more dense and sinks in the water. But the lemon lime mystery is a little different.

We have to turn to the Internet for more information. According to the USDA website, a lime is 88.26% water by weight and a lemon is 87.4%. This could mean that lemons have a higher air content, but we're still not sure.

So, our next step was to weigh the lemon and the lime. Digging through our grocery bag of lemons and limes, we found two that were very similar in size and weight. Both the lemon and the lime weighed exactly 101 grams. If you know the weight, it only makes sense to determine the volume of each fruit. Using displacement of water, we determined that the lemon had a volume of 99 mL and the lime had a volume of 90 mL. You might remember doing this in school when you learned about volume. Fill a container to the very top with water and then submerge the item (the lemon in this case). Collect and measure whatever water spills out over the edge of the container and you've got the volume.

So, using the density formula (D=M/V) it was easy to determine the density of each fruit.

The Lemon: Density =101g/99 mL = 1.02 g/mL

The Lime: Density = 101g/90 mL = 1.12 g/mL

Since the density of water is approximately 1 g/mL, it makes sense that the lemon in our experiment floated and the lime sank.

But we're still a little confused as to why limes sink and lemons float. Some people have suggested that lime flesh is much more dense than lemon flesh and, as a result, it holds its juice better. People who "juice" fruits know about this phenomenon. If you want to get more juice from a lime, warm it up in the microwave briefly and then firmly roll it along the worktop before slicing it lengthways and juicing it. It makes a huge difference.

Since the density of the lemon and lime are very close to water, even very small changes in composition could mean the difference between sinking and floating.

Click the thumbnail below to see the video.

• Soda Surprise
April 23rd, 2012

 Lemons and Limes! Ariel M.    -  January 27, 2013 This user gave 5/5 stars It was fun. The lemons floated. The limes sank. I did the experiment with my friend Ewan. I am 6 and Ewan is 5. We are going to show our results at a science fair on Friday. my science fair project zoomy    -  November 28, 2011 This user gave 5/5 stars ths was a kool thng to do for my science fair project the lemons did float and the limes did sink some floated a little but not really. but why did the lemons float and limes sink? their pretty much the same. Limes all floated disappointed    -  April 26, 2011 This user gave 3/5 stars My daughter and nephew tried this for a school project and both the limes and the lemons sank. They used 3 or 4 of each fruit and everything floated. We peeled the fruit for them and then everything sank, both the lemons and the limes. The peels floated. Conclusion - the skin is what makes the fruit float. Sort of works Annie    -  April 17, 2011 This user gave 4/5 stars we found a lemon and a lime that were the same size, and they both floated. BUT the lemon floated more than the lime doesn't work Abby    -  March 12, 2010 This user gave 3/5 stars This experiment does not work- I tried it with many size lemons and limes and they all float! Nothing sinks! Abby- Keep trying the limes. We had a few that floated as well, but the majority of them should sink. -Spangler Science Customer Service Team My project... broc North Carolina   -  November 29, 2009 This user gave 3/5 stars I used this for a science fair project at school. I just wanted to say that I had different results. My limes did sink, and my lemons floated, but whenever I took the rind off of the lemon, it went straight to the bottom of the bowl. So in my project I stated as my conclusion that the reason why lemons float but limes sink is because the lemons have a porous rind. I gave this 3 stars because it was a good idea, but the reason stated in the passage (according to my lemons and limes) were wrong.

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