PI Problems for the Physics Suite Edward F. Redish

Peer Instruction Problems:
Oscillations and Waves

 Problem Name Comments Source Demo (UMd) O01. An asymmetric pulse This is quite a bit more challenging than it looks on the surface. Introductory students often tend to want to make all graphs look the same and they are not used to doing the work of translating a physical situation into a graph. Even if this has been stressed in the kinematics study in the first term it is well worth bringing it back in this more complex (two independent variable) situation. O01-d is an alternative version with the answer not given so it can be drawn from the class. EFR O02. Do the math Matching what they know about functions to what they know about the physics of a propagating pulse can be difficult for some students. Try this one and see whether they all get this "obvious" one. If not, it can lead to an interesting discussion of working with the math (do a specific example of a particular function) to see how you can know what it has to be. EFR O03. Adding two pulses The idea that when two pulses overlap the result is the point-by-point sum of the two functions is not intuitively obvious. This problem may produce some surprising ideas from your students. Don't just ask what they think will happen, try asking them to explain why they chose the answer they did! Often, it shows they try to reason globally rather than locally and qualitatively rather than mechanistically. EFR O04. Building superposition 1 This and the next two problems help the students to develop the rule for superposition: that the "message" sent to each bit of the string as to how to displace by the two pulses are added algebraically. As we see in the previous problem, students want to get some result "in between" the two pulses and get answers that do not satisfy superposition. Although this and the next two examples are not realistic (no sharp corners on a string), the binary choice is much easier for them to deal with than a more realistic case. I always mention that this example is not realistic but will help us build a realistic rule. The way this is phrased, you have to draw answers from the class. EFR O05. Mass on a spring graph reading: 1 As we saw in the kinematics region, students often have trouble interpreting graphs physically. This nice problem from Mazur requires some serious interpretation taking a local perspective (looking at what is happening at a particular instant in time). From the ConcepTest collection in Mazur's Peer Instruction O06. Mass on a spring graph reading: 2 Another graph reading problem for a mass on a spring. This requires taking a more global perspective. From the ConcepTest collection in Mazur's Peer Instruction O07. Mass on a spring force Some students may still be confused about isolating instants of time and identifying forces specific to that instant. This probes that issue quickly and directly using the hanging mass. Answers need to be drawn, but getting the students to articulate the force possibilities is a useful thing. If someone suggests "a force in the direction of motion," let them do it and include it in the possibilities to see how many still have this misconception. &EFR

Work supported in part by a grant from the US National Science Foundation.

Maintained by Edward F. Redish
Comments and questions may be directed to redish@umd.edu

Page last modified February 8, 2005