Tutorial details

Section I: Properties of pulses

This section involves a series of video observations of pulses traveling along a spring. From the first video, students recognize that the amplitude, width, shape, and speed of a pulse do not change significantly as the pulse travels.

In the video that follows, students observe how the speed of the pulse is affected when the (1) pulse amplitude, (2) pulse width, and (3) spring tension are changed. From these observations, students infer that the speed of a pulse depends on the medium through which it travels rather than on the features of the pulse itself.

Section II: Superposition

Students examine two time sequences of photographs in which two pulses on a spring approach one another. In the first case, the pulses are on the same side of the spring; in the second, the pulses are on opposite sides of the spring. Students are led to recognize that the principle of superposition can be used to determine the overall shape of the spring.

Section III: Reflection from a fixed end

Students examine a time sequence of photographs that depict the reflection of a pulse from a fixed end. They are led to recognize the similarity between (1) reflection by a fixed end and (2) superposition of two pulses on opposite sides of a spring that approach each other. This similarity motivates a model for reflection from a fixed end: we can treat the spring as if it extends beyond the fixed end and imagine the pulse incident on the fixed end is met by a pulse passing the other way so that the end of the spring remains stationary. Students use this model to determine the shape of a spring while an asymmetric pulse is being reflected.

Section IV: Reflection from a free end

Students are presented a scenario in which a pulse is sent along a spring toward a free end. The spring is surrounded by cups placed along the floor. Students predict which cups, if any, are knocked down during the reflection, then observe a video demonstration.

The video demonstration in this section is necessary for the homework.

For instruction tips, login or register as a verified educator to see the Instructor Guide.

Students should have previously studied basic kinematics and the principle of superposition.

Equipment

List

• tutorial instructor slides
• tutorial student slides or worksheet

Resources and Links

https://www.youtube.com/watch?v=ka7tDwfKaG8, https://youtu.be/nfksFCmrzHo, https://youtu.be/1uibf6dh_XU

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