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## 08 April 2017

### For April AP Physics 1 classes: Here's a list of experiments, go do them.

At this point in my senior-level AP Physics 1 class, we have learned all necessary fundamental skills.  We have practiced solving problems with forces, motion, energy, momentum, rotation, circuits, and waves.  We have learned the critical laboratory skills, including how various equipment works, how to present data graphically, and how to use the slope of a graph to analyze data.

In the last month of the course, I'm using class time to put all these skills together in practice.

I have two 90 minute classes each week.  In these, I've been starting with 20 minutes or so of preliminaries: a TIPERS-style quiz, discussing the quiz, taking questions on homework.  Then I release the class to play.

What do they play with?

I've given the class a list of seven experiments; I can come up with more as necessary.  The list is below.

A student picks one and begins work.  I am happy to help with equipment questions, but not with "how am I supposed to do this?" questions.  (For those, I ask them to collaborate with a classmate.  That works at this stage of the year.)

How do they report their results?

Very informally.

I ask for a few sentences describing what they measured, and what equipment they used to make the measurements.  I ask for a few sentences describing how the data was analyzed, and how the data answers the question posed.  That's it.  No "formal lab report", no "purpose / procedure / results / conclusion."

Sure, occasionally I get a student who tries to give me a page with a bunch of messy numbers on it.  I simply send him back to his desk to do it right.  But this removal of formality in lab work has worked wonders for years.  It mimics what students will be asked to do on the AP exam -- in just a few minutes, writing by hand, describe an experiment including procedure and analysis.

What if I don't have enough equipment for everyone for these setups?

Part of the beauty of this approach is that I never have more than a couple of folks at a time working on each experiment.  Students are directed to work in any order they desire.  Often they will choose based on which experiment's equipment is available.

If several labquests are on the fritz - as they often are - it doesn't matter.  Because (a) students will have incentive to choose an experiment that doesn't involve the labquest, and (b) students will have incentive to figure out new and interesting methods for measuring what the labquest can measure.  For example, rather than plug in motion detectors to the labquest, they might learn to use video analysis on their phones.

Here's my list.  Each one can take anywhere from 20 minutes to an hour.  You'll recognize some 'cause they're inspired by old AP problems.  One (number 7) was created by a veteran of my class when he needed a project in another class.  I'll probably post some other time with specific notes about each... but for now, these have been a good start to independent lab work in the spring.

1. A transverse wave is traveling on a string.  If the frequency on the wave machine is doubled, what is the new average speed of the point?  Use a high speed camera on slow motion to directly measure the average speed.

2. Use a pipe, a meter stick, and a frequency generator to determine the speed of sound at room temperature.  Find somewhere with a temperature below 50 degrees F, redo your measurement, and see if the speed of sound has changed.

3. A 1 kg object traveling on a frictionless horizontal surface collides head-on with and bounces off of a 0.5 kg object initially at rest.  Give experimental evidence for (a) the percent of total linear momentum that was conserved, and (b) the percent of total mechanical energy that was conserved.

4.  In the circuit shown above, the sum of the resistances of resistors R1 and R2 is 80 kΩ.  Resistor R1 and the 80 kΩ. resistor are now swapped.  A student claims that the current must always increase in the right-hand branch of the circuit, because the total resistance of that branch must decrease.  Test this claim experimentally.
.

5. Create two pendulums: one with 50 g of hanging mass, one with 100 g.  Release both from the same angle.  Predict and give experimental evidence to show how each of the following differ for the two pendulums:
Period
Maximum kinetic energy
Maximum acceleration

6. We’ve learned that the period of a pendulum is independent of the amplitude.  Provide experimental evidence for this claim; present your results graphically.

7. You are given two objects to be placed on either side of a pivot, as shown above.  The total mass of the two objects is known.  You may vary the distances from the pivot at which you place the objects.  Use the slope or intercept of a linear graph to determine the mass of each object experimentally.

1. My variation of the pendulum experiment: "Test two hypotheses: 1. A pendulum's period is independent of its mass, and 2. A pendulum's period is independent of its starting amplitude. State whether your data support or debunk the hypothesis given. In each case, use a graph of your data to support your claim."

There were a couple of lab groups that got significant enough differences at high angles to debunk the second hypothesis, and we had a nice discussion centered around the wikipedia article for mathematical (not-so-simple) pendulums. Also: equally beneficial discussion of why lab groups that picked data points every 15 degrees tended to get more informative results than those that only tried very small angles (one group actually did 1-degree increments up to 15 degrees and stopped there; they had more data points than everyone else, and yet...).

2. This does not have to do with this lab post, but I wanted to put a question to the group who follows this blog. The Physics 1 exam description says 50 MC questions, but it seems like all of the secure exams available through the course audit page have 40 questions. Does anyone know how many MC questions will be on the actual exam this year?

3. Aaron, please see the post of April 17 2017. There will be 50 mc on the actual exam.

4. I assume in #4 you meant R1 and the 20kohm resistors are swapped, not R1 and the 80kohm. I haven't had coffee yet this morning, so maybe I'm missing something.

5. I assume in #4 you meant R1 is swapped with the 20kohm, not the 80kohm?

6. I'm really impressed that you can get to April having learned all the fundamentals. I love the idea of letting the class play at the end and really apply what they've learned, but in my planning and from the AP pacing guides I can't seem to find enough time. Do you have your own pacing guide or schedule that you would be willing to share?