Download Air Resistance Through Straws

Air Resistance Through Straws
Purpose: To explore air resistance in straws and to make the analogy to
electrical resistance; to investigate the difference in resistance between resistors
(straws) hooked in series and parallel
Introduction: How do light bulbs affect the movement of charge through
themselves while a capacitor is charging and discharging? Do they determine the
amount of charge that can flow through? Do they determine the rate at which the
charge can flow through? What does the brightness of a light bulb tell us about
the movement of charge through the filament? A series circuit of resistors is one
in which there is only one path through which the charge can travel. A parallel
circuit is one which there are multiple paths through which the charge can travel.
Materials: 3 soda straws and 5 coffee stirrers
Procedure: Part A: Investigating the Relationship Between Resistance and
Cross-sectional Area
Sometimes it isn't easy to imagine how charge flows through wires, but it's
always easy to blow air through straws.
Take a standard soda straw and cut it to the same length as a coffee stirrer. Blow
gently through each straw. Notice how much effort is required to move air
through the straw and how readily the air flows through. Record observations.
1. Which straw is easier to blow through? Which straw has the greater flow rate
of air passing through it? Which straw has the greater resistance to the flow of
air?
Procedure: Part B: Investigating Resistors in Parallel
Take five coffee stirrers and tape them together to form one "bunched" straw
(Figure 3.13a). Blow through the "bunched" coffee stirrers and then blow through
the single soda straw. Record observations.
2. How does the difficulty of moving air through the single straw and the bunched
stirrers compare? Which of these straws can be compared to a parallel
combination of bulbs?
3. Remove one or two coffee stirrers from the "bunched" straw and blow through
the remaining ones. Has it become more difficult or less difficult to blow air
through the "bunched" straw? Compare this to how the resistance of a parallel
combination of bulbs would change if some of the branches were removed.
Procedure: Part C: Investigating Resistors in Series
Take two straws and tape them together to make one longer straw. Blow
through the longer straw and then through a single straw. Record observations.
If there is no distinguishable difference, tape three straws together to make one
longer straw and repeat. Record observations if necessary.
4. Which is easier to push air through, the single straw or one two or three times
as long? Compare this to how the resistance of a series combination of bulbs
would change if more bulbs were added.
5. The equation which determines the resistance of a resistor is R =  l / A ;
where R = resistance in ,  = resistivity based on the material in m; l = length
of the resistor in m; A = cross-sectional area in m2. Based on this equation, why
was it important to have both types of straws cut to the same length in Procedure
A?
6. Based on the equation given in Question 6, what is the relationship between
the length and the resistance? Did Procedure C verify this relationship? Explain
why or why not.
7. Based on the equation given in Question 6, what is the relationship between
the cross-sectional area and the resistance? Did Procedure A verify this
relationship? Explain why or why not.
8. What material serves as the substance through which the “current” is flowing
in this simulation? Is the substance the same when using the coffee stirrer and
the drinking straw?
Write this up as a formal lab report: Include the following sections:
Page 1: Title; Introduction (give purpose); Procedure; Page 2: Data (include
observations from all three procedures); Page 3: Results – errors introduced
during the lab? Conclusion (respond to the three elements in the Purpose);
Questions (there are 9 of them). Do NOT turn in this handout!