Activity Set #2: See? Compare? Question? Test?

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What is there to observe?To what could/should we pay attention? How can we determine which variables affect the system in what ways?

The Setup for this Activity is the same as the last:

After coming to a consensus on the pendulum system, the two side-by-side pendula are set in motion from different angles (one has extra washers on the string above the bob, the other has a longer string).

Part I: Small group whiteboarding task:

•What do you see?
•What could you compare?
•What questions could you ask?
•What comparison could you carry out to answer your question?
•What factors would you need to keep the same (control), to ensure that your comparison a "fair test"?

Discussion circle to share observations, establish terms and distribute experimental tasks:

 

Glossary entrees/ Words to discuss meaning:

factor
variable
control (as verb)
"fair test"
controlled experiment
control (as noun)
full swing
period
repeat time
oscillation
arc
arc angle
arc length
string length
bob
mass or weight (not distinguished)
phase
in phase
out of phase
amplitude
decay

Part II: Groups carry out qualitative comparisons of paired pendula to determine which variables effect the system in what ways.

•Self-designed small group experiments and whiteboarding of result

Potential seeds:

Are adding washers a fair test of the effect of mass? Is anything else about the bob changed? What would be a "fair test" (Have matched bob's ready)

If it is very hard to determine when a pendulum is done swinging, how else could compare which amplitude is decaying away faster?

How could we which pendulum is moving faster at the bottom of the swing?

How could the pendulum have a larger swing and take almost the same amount of time?

 
Glossary entrees/ Words to discuss meaning:

mass or weight distribution
uncontrolled experiment
speed
maximum speed
compensate, compensation
constant
proportion
coherence
half-life
air resistance, friction
energy
energy dissipation

Whole group discussion of results. Using paired pendula as demonstration groups can present observations.

Relations identified:
 

•  Increased speed compensates for increased distance to travel when we vary the angle.

•  Distance traveled in one swing is propotional to angle and length of string.

• Increasing the weight/mass decreases the decay in the amplitude of the swing, but does not effect the period when we keep the volume and shape the same.
  

•  We can characterize the coherence by counting the number of swings that it takes for the pendula to get out of phase.

•  Mass distribution of bob can affect the period through changing the effective length of the string.

•  Maximum speed and period both increase as we increase the length of the string.

•  Increased average speed partially but not completely compensates for increased distance to travel when we vary the length of the string because the period also gets longer. Both increased average speed and increased time for each swing contribute to the increased length of the swing as the string gets longer.