1-hole rubber stopper and glass tube assembly that fits the mouth of the
bottle.
ruler
Small quantity of water
Geometry formula: Volume of cylinder = p r2
h
Teacher's Note: This activity involves thermal
expansion: a volume change that results from a change in temperature, rather
than material being introduced or leaving.
Place a drop of water into the glass tube as shown.
Put the stopper into the bottle, being careful that the water drop is not
expelled from the tube as the stopper is pushed in. (Important: If
the glass tube is not already pushed through the stopper, ask the teacher
to do it for you; this is a potentially hazardous task!)
Use the ruler to estimate the volume of the jar, in cubic centimeters.
(You will need to measure the diameter and height of the jar, and assume
it is a cylinder, using a handy formulas from geometry class). If
the jar's capacity is labeled, this will be a more accurate number to use.
Volume = _______________________
Use the ruler to measure the height of the water drop above the stopper:
_____________
Place your hands around the sides of the jar for one or two seconds only,
to warm up the jar slightly.
Observe the water drop: it should start to move. If it does not move,
put your hands around the jar again (or find someone with warmer hands!)
until the drop does start to move.
Which way does the drop move? _______________________
What does this tell you about the air inside the jar? _________________________
Is any air being added to, or removed from, the air-stopper-tube system?
_________ Explain your answer: ___________________________________________________
After the drop stops moving, measure its new height above the stopper:
_____________ and calculate the distance the drop moved: ____________
Use the ruler to estimate the inside diameter of the glass tube: __________
Using formulas from geometry, estimate the additional volume that the air
in the jar takes up after it has been heated: ____________________
Estimate the fractional change of volume this represents: ____________
The coefficient of thermal expansion is a number that describes the fractional
expansion of a substance for each degree Celsius; its units are (fractional
volume) / (degrees Celsius). If the temperature inside the jar was
raised by three degrees C from your hands, estimate the coefficient of
thermal expansion for air: _____________
Oceanography Connection:
The coefficient of thermal expansion for sea water is about 0.00021 (fractional
volume change per degree C); often this parameter is written as b
= 2.1 ´ 10-4 ° C-1.
Because the length and width of an ocean basin does not change as the ocean
is heated slightly, b also describes the change
in height as the water warms or cools. The relation between change
of height D h, ocean depth D and temperature
change DT is: D
h = b D DT
If an ocean basin is 5000 m deep and you know b
(above), calculate the change of temperature of the entire ocean that would
be needed to cause a 2 cm change in sea level: _______________________________
