Observations and results
Why did two different materials from the meat that were the same size (thus had about the same volume) do different things in the water? How could two pieces of bread that started out the same (thus had about the same mass) do different things in the water?

These two different results happened because the objects had different densities (which is determined by a combination of volume and mass). If an object has a greater density than water, it sinks. If it is less dense than water, it floats. Which type of body material—muscle or fat—had greater density than water and which had a lower density?

So, as it turns out, athletes with very little body fat might have to work harder to stay afloat in the water. To be healthy, our bodies need a balance of fat and muscle.

Some animals that live in the ocean have a thick layer of fat called blubber. Blubber helps to keep these animals warm, but how else might it affect a whale or manatee in the water?

Have you ever been swimming in the ocean or a salty sea? If you have, you might have noticed that it's easier to stay afloat in the saltwater than it is in a lake, pond or swimming pool. Why is that? Salt dissolved in the water makes it more dense. So even if you haven't changed your body composition, you are less dense relative to the salty water, which helps you float on the surface. You can demonstrate this effect at home by filling two glasses with warm water and dissolving about six tablespoons of salt into one of them. Gently place an egg in each glass, and see what happens.

Share your muscle versus fat observations and results! Leave a comment below or share your photos and feedback on Scientific American's Facebook page.

Cleanup
Pour out water and throw away bits of bread, meat and fat (or compost them if you can).

More to explore
"Going for the Gaunt: How Low Can an Athlete's Body Fat Go?" from Scientific American
"Do Giraffes Float?" from Scientific American
"Floating Eggs In Salt Water" activity from Reeko's Mad Scientist Lab
"Your Muscles" overview from KidsHealth
Will It Float or Sink? by Melissa Stewart Page, ages 4–8
Head to Toe Science: Over 40 eye-popping, spine-tingling, heart-pounding activities that teach kids about the human body by Jim Wiese, ages 9–12

Up next…
Color Changing Dots

What you'll need
•    Five to 10 different colors of construction paper
•    Hole puncher
•    Bowl
•    Colored fabric or different color surface (optional)
•    Timer (optional)

3 Comments

1. 1. desertchyuoto 04:13 AM 5/12/11

   Katherine Harmon:
   
   "Animals have a lot of the same insides as we do..." "Within most of the human—and animal—body, whether muscle, fat, blood or bone, is a lot of water."
   
   I don't usually make it my business to correct people that know more than I do. However, the lexicon of empirical experiments should include proper taxonomy. Humans are not similar to animals -- we are animals.

   Reply | Report Abuse | Link to this

2. 2. HubertB 07:20 AM 5/14/11

   Now I have an excuse to over eat. Then I can get fat and float on top of the water instead of sinking to the bottom of a swimming pool like a rock as I now do!

   Reply | Report Abuse | Link to this

3. 3. verdai 07:35 PM 5/15/11

   O boy.

   Reply | Report Abuse | Link to this