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Whelmer #42: Fire Sandwich
Description:
A burner flame is prevented from passing through a piece of wire screen.
Science process skills:
- observation
- communication
- interpreting data
Complex reasoning strategies:
- comparison
- deduction
- supporting
Standards:
K-4:
- Employ simple equipment and tools to gather data and extend the senses
(Standard A.1.3).
- Heat can be produced in many ways. Heat can move from one object to
another by conduction (Standard B.3.2).
5-8:
- Energy is a property of many substances and is associated with heat
and light (Standard B.3.1).
- Heat moves in predictable ways, flowing from warmer objects to cooler
ones, until both reach the same temperature (Standard B.3.2).
9-12:
- Chemical reactions may release or consume energy. Some reactions such
as the burning of fossil fuels release large amounts of energy by loosing
heat and by emitting light (Standard B.3.2).
Above Standards from the National
Science Education Standards.
Content topics:
- combustion
- heat conduction
You will need:
- Bunsen burner
- matches
- several 4" x 4" wire screens
Instructions:
You will be moving your hands and arms around a lit burner. Follow all fire safety
precautions with this activity.
Light the burner. Slide one of the screens over the top of the burner tube.
The flame continues to burn through the burner. Remove the screen.
Slowly bring the screen down over the top of the flame. This time the flame
does not go through the screen.
Slide the screen over the top of the tube of the lit burner. The flame continues
to burn through the screen. Slowly lift the screen one or two inches. The
flame burns above the screen but not below.
Use two screens. Again, "lift" the flame from the bottom while bringing
the second screen down from the top. The flame will be trapped between the
two screens: a fire sandwich!
You can make a "reverse fire sandwich" by inserting two screens in mid-flame
and slowly separating them.
If the screens heat up too much, they will stop being effective for this
demonstration.
Test the pieces of screen before presenting this activity. Some gauges and
alloys of wire conduct heat better than others.
Presentation:
Remind students that manipulating flames can be very dangerous. This should
not be repeated at home.
Question students at each stage of the presentation. Ask them to analyze
why the flame is on one side of the screen and not the other. Surely the
holes in the screen are large enough to allow gas and air molecules to pass
through. [They are.]
To demonstrate that the gas and air mixture is indeed passing through the
screen, hold a lit match over the screen that has a flame below and no flame
above. The gas ignites above the screen.
What is the difference between the gas below and the gas above the screen?
What effect does the screen have on the flame or the gas?
Content:
The wire screen conducts heat away from the flame, cooling it below its
combustion point. The gas and air remain, but they are much cooler.
In the early 19th century, coal miners suffered explosions of gas and coal
dust, which were ignited by the candles on their helmets. Sir Humphrey Davey
of the Royal Institution found a simple cure to their problems. He designed
a screen envelope for the candles and oil lamps used in mines. The flame
within the wire cages illuminated the mine, but greatly lessened the risk
of explosion.
Assessment:
Type: individual.
Content/Process: combustion, heat conduction.
Age/Level: middle school and higher.
Students should observe the demonstration and describe the basis for the
phenomena. Discussions should focus on the dispersion of heat by the wire
screens, thus lowering the temperature of the gas, inhibiting combustion.
Notes:
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