Expansion of object with added air

Materials: zip-lock baggie straw pencil ruler meter stick water plastic spoon

In this activity, the expansion of the object is directly related to the amount of air introduced through the straw.
Teacher's Note: This activity introduces students to the concept that the volume change of an object is quantifiable, and can be calculated by measuring the changing height of the pencil, and the bag's width and length.  The ocean, too, expands and contracts as its temperature changes; its volume changes slightly, although the amount of water remains constant.

1. Insert the straw into the sealable baggie, and close the bag around the straw.  The seal will not be air-tight, but you will still be able to use the straw to add air to the bag, as long as the bag is not very full.
2. Position the ruler vertically on the table top, with "zero" downward.  You might want to balance the ruler against some books.
3. Without the baggie, put the pencil directly on the desk top, with its point touching the ruler.  Record its position here: ____________________
4. Put the baggie on the table top, and put the pencil on top of the baggie, as shown, with the point touching the ruler.
5. With a very small amount of air in the bag, read off the position of the pencil, and record: ____________
6. Figure out the starting height of the bag from these measurements.
7. Measure the bag's length and width, and do a very rough calculation of the starting volume of the bag (assume the bag has a constant height). Volume: ________________
8. Now gently puff a small amount of air into the baggie.  Record the new position of the pencil tip (either you or your partner should read this off). New height: _______________________
9. Calculate the new height of the baggie: ___________________
10. Figure out the percent change in the baggie's height:  _______________
11. Figure out the percent change in the baggie's volume: _______________
12. What do you notice about how these two fractional changes are related? _____________
• Teacher's note: These two fractional changes are the same, because the width and length of the baggie has not changed.  In the same way, when the ocean height changes because of thermal expansion, the ocean's width and length do not change, and the fractional volume change is the same as the fractional height change (which is very small!)