Sometimes It Will Float by David Drew

Teaching ideas

We often teach children that "corks float" and "metal sinks." This leads to problems: modern ships are made of metal, but they float. If you tie a cork to a stone it will sink. This book helps you sort out these problems.

Sometimes It Will Float is a book of visual instructions showing how to test items to see if they will float or sink.

In the following notes I give some explanations about why things float or sink. You need not go into this amount of detail yourself. The key idea is density. I mention density only because someone in the class might ask you "Why?"

"You will need . . ." (page 2)

We start with a visual list of items to test. Make sure you have these ready to use - either while reading the book, or after reading it.

Labeled diagram. This page is a labeled diagram. Items in the diagram are given their names as labels. For very young readers a labeled diagram can be more helpful than a word list. The pictures help them to find the word they need.

The bottle (page 3)

Cover the bottom half of this page, so that the children look at one experiment at a time. Point out the numbers 1, 2, and 3. They tell us the order in which to read the steps.

Children need to look closely at the details. Is the bottle full or empty? (It is empty of water. It is full of air.) Can the air get out? What if we pushed the bottle under the water? (The air would still stay in, because this bottle has its top screwed on.)

Now reveal the bottom of the page. What is different about the bottle? (The top has been removed. Otherwise the bottle is the same.)

Now what happens when we pull the bottle under the water? (The air escapes as bubbles. The water rushes in to take its place.) This is why the bottle sinks. When it was full of air it floated. Now that it's full of water it sinks. So air is important in floating. It is as important as the water.

Remind the children that this is the same bottle as in the storyboard at the top of the page. Only the bottle's top has been removed.

Storyboards. Each page, starting with page 3, shows us a pair of storyboards. A storyboard is a visual text in which we see steps in a sequence. They can be numbered, as in this book, or they can have arrows that connect each step to the next. Storyboards show us changes over time. They usually show us changes that happen to the same thing.

The bowl and the stone (pages 4-5)

Turn the page and cover all but the top half of page 4. This ensures that the children look closely at the details of each experiment before moving to the next.

Draw the children's attention to the details. For example, the bowl is lowered into the water while being kept flat or level.

Now reveal the bottom half of page 4.

Ask if there is anything different between Step 1 in each of the storyboards on this page. The children will tell you that this time the bowl is tilted. You can suggest that this tilting might be what made the bowl sink. Remember, it is the same bowl. In the top storyboard the bowl still has some air captured inside it. In the bottom storyboard we let the air escape by tilting it. Just like the air that escaped the bottle on page 3.

You can also tell the children that things that float in water are less dense than water. This is better than saying that it is "lighter than water" or "weighs less than water". Density is mass per volume. Put it this way: "A bucket of water is heavier than a bucket of air." In both cases the bucket is the same - it holds the same amount (volume).

The bowl is denser than water. It will only float if it can capture some extra air.

On page 5 the stone is much denser than water. Moreover it has no hollow part that can capture air as the bowl did. No matter how we tilt the stone, we cannot make it float. The only way to make this stone float is to put it in the dish, because the dish, unlike the stone, can capture some air.

The cork and the jar (pages 6-7)

Continue as before, showing the storyboards one at a time.

Cork is the bark of a cork tree. Cork floats (page 6) because it has a high ratio of air to wood. This is where density is a more useful idea than weight or mass when explaining why something floats. If you say that cork floats "because it is lighter than stone," then you have a problem if someone in the room asks you, "But what about a ton of stone? That will still float. And only half a ton of stone will sink. The cork was twice as heavy, but it still floated." So it can't be just weight or mass. Instead, it's all about the weight or mass of every equal-sized piece. A bucket full of cork is lighter than the same bucket full of stone. Or the same bucket full of water.

The jar (page 7) is rather like the bottle (page 3), but this time we fill the container with either air or water and use a lid in both cases. This makes clearer the fact that the only change that has occurred is the change from air to water. A jar full of air is less dense than the same jar full of water.

Will it float? Will it sink? (page 8)

The last page is like the first (page 2), in which we had a labeled diagram of items to test. But this time the children will have to discover for themselves which ones float or sink, and how we might change something to make it sink or float.

The children can predict what might happen. This is called a "thought experiment," in which you imagine doing the test. The next step is for groups of children to take turns at a tub of water and try for themselves . . .

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