1. “The Pendulum Conundrum”
Pendulum Behavior Lab
“The Pendulum Conundrum”
Student will complete a lab where, working as a group, they organize their seating in alphabetical order from Z-A following a prescribed pattern. Steps of the scientific method will be linked to the process. Students will learn the link between everyday activities and the use of the scientific method and its steps.
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2. Pendulums can be used to measure time.
Help me understand what factors make it so.
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3. The time it takes for a pendulum to swing back and forth once.
Based on our discussion, how would you define the term “period” as it relates to the behavior of a pendulum?
The time it takes for a pendulum to swing back and forth once.
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4. Now let’s investigate two of these factors:
As we have seen, several factors influence keeping time with a pendulum.
Now let’s investigate two of these factors:
Mass and Length
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5. Make individual predictions
The length of a period is measured in seconds. Predict what you think will happen when you increase the amount of mass hanging from the end of a pendulum by plotting on the first graph. For example, if you double the mass, will you double the period as well? Predict what you think will happen when the length of the string of the pendulum is increased by plotting on the second graph. For example, if you triple the length, will you triple the period?
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6. How we will collect data
A period is one complete swing, over and back.
You will count and time for ten periods.
You will work in groups of three, ideally.
One student counts
Two students time
You may use your phone/iPod/etc. as a timer
We are measuring mass in units of “washers;” we assume each washer has the same mass.
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7. Data Collection Chart Trial # 1 2 3 Totals Average (sec/pd) Total time
[For each station: one counter and two timers]
Trial # 1 2 3
Totals
Average (sec/pd)
Total time
(for both timers)
# of Periods (x2)
Lab Stations: M2, M4, M6, M8, M L25, L50, L75, L100, L125
(circle yours)
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8. Procedures/Data Collection
Show me your graph shape predictions on the way to the lab station.
Go to your assigned group.
[The letter and number in the corner of your lab sheet match the label at a specific lab station.]
Record data for three trials.
[total time for 10 periods (full swings)]
Return to seats with your group when finished collecting data.
Discuss your graph shape predictions with your lab groups & record a group prediction.
Write group data on the board.
Discuss as a class.
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9. Place data on graph when called
After collecting your data, please return to your seats as a group, address the lab questions, and wait for your group to be called on.
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10. Discussion of Results Conclusions: T = 2π length/acceleration (g)
Mass has no impact on the period of a pendulum
Length does impact the period of a pendulum
… but it is not a linear relationship.
… It is actually a square root function!
T = 2π length/acceleration (g)
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11. Complete “Exit Ticket” Turn in on your way out of class.
Think about today’s activity: Assume the pendulum length starts at 1.5 m and its period is 2.5 sec. Predict the length of the period if the pendulum’s length is increased to 3 meters. Explain your reasoning. (Consider the graph; the line was not straight.)
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12. (c) Copyright 2014 - All rights reserved www.cpalms.org
The
Pendulum Behavior Lab
“The value of “g”
Student will complete a lab where, working as a group the organize their seating in alphabetical order from Z-a following a prescribed patter. Steps of the scientific method will be linked to the process. Students will learn the link between everyday activities and the use of the scientific method and its steps.
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13. Pendulum Lab – clearing misconceptions
Length does impact the period but it is not a linear but a “square root” type of relationship
As with free fall, mass has no impact on
The length of the period
T = 2π L / g
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“The math of g”
T = 2π length(L) / acceleration(g)
To solve for “g” we need to rearrange the equation.
T2 = 22π2 x length(L)/acceleration (g)
Square both sides
Divide both side
to get g by itself &
cancel common terms
T2 = 22π2 x length(L)/acceleration (g)
22π2 x length
22π2 x length T2
4π2 x length(L) 1
acceleration(g) =
simplify
4 π2 x L T2
Invert
(take the reciprocal) =
“g”
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“The math of g”
Station #
same as yesterday’s
Trial #
Length
(in meters)
Time for 15 oscillations
Period (T) (in seconds)
T (total) /15
Value for T2
g = 4π2 L/T2
(4π2 = 39.44)
# 1
# 2 #3
Calculating the value of “g” using a pendulum
AVG.
Lab Stations: M2, M4, M6, M8, M L25, L50, L75, L100, L125
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MASS
“g” M2 M4 M6 M8
M10
LENGTH
“g”
L25
L50
L75
L100
L125
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