Key concepts
Density
Body composition
Muscle and fat

From National Science Education Standards: Characteristics of organisms

Introduction
Your body has a lot of different kinds of materials in it. There are, of course, bone, blood, fat and muscle—just to name a few.

But all of these parts are hidden away under our skin, so how can we learn more about some of their qualities? Animals have a lot of the same insides as we do, so we can learn some interesting things about our bodies by studying something as basic as meat you can buy at the store. One easy and fun test to do is examining whether substances float in water—which tells us how buoyant they are. More about buoyancy in a moment.

Background
Some components of the body are denser than others. Try this activity to discover which substance is denser than water: muscle or fat. If a substance is less dense than water, it will be buoyant, meaning it will be more likely to float.

Density is determined by an object's mass and the amount of space it takes up (its volume). This is why heavy metal ships can float on the water—they're big enough to have an overall density that's less than that of water, but if you crushed them down into a ball and got rid of all of the empty space, the metal ball would sink, well, like a rock!

Within most of the human—and animal—body, whether muscle, fat, blood or bone, is a lot of water. This means our bodies really are close to the density of water. But this activity can also help explain why some animals—and people—are more buoyant than others.

Materials
•    Cooked piece of meat that has both lean meat and fat on it (such as a pork chop or steak)
•    Knife to cut the meat
•    Piece of bread
•    Large clear glass cup or bowl
•    Water

Preparation
•    Fill the clear glass cup or bowl with water.
•    Tear off two big pieces of bread that are about the same size.
•    Set one on the counter as is, and smash the other into a dense ball.
•    Carefully cut a piece of fat off of the meat.
•    Carefully cut a piece of lean meat that is about the same size as the fat.
•    Do you think any of these four items will float in the water? Why or why not?

Procedure

•    Place the cut piece of animal fat in the water. What happens?
•    Now put the cut piece of lean meat in the water. What happens to it?
•    Now place the un-smashed piece of bread in the water. What happens?
•    Remove the bread, and now place the densely smashed ball of bread in the water. What happens to it?

Read on for observations, results and more resources.

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.

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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!

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

   O boy.

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