Part II: Traveling Pulses and Barriers

Pulse 1 Pulse 2 Hard Barrier Soft Barrier

Please wait for the animation to completely load.

A string can be approximated by many connected particles as shown in the animations (position is given in meters and time is given in seconds).  Restart.  Here we consider a pulse on a string and looks at the motion of the individual particles that make up such a string. 

Look at Pulse 1 (push "play") which shows a Gaussian pulse incident from the left.  Now, look at Pulse 2 which shows a Gaussian pulse incident from the right. 

  1. Do the individual particles travel in the horizontal direction?  What about the pulse itself?

In the other two animations the pulse is incident from the left and hits either a Hard or a Soft barrier. The hard barrier example is depicted by the hand that represents a string whose end is tied down; the soft barrier example represents a string with one end free. 

  1. Describe the differences between the waves reflected at the two barriers (Hard or Soft ).
  2. Explain those differences.

One way to think about a pulse hitting a barrier is to consider the pulse that you see as a superposition of two pulses: the one traveling into the barrier and the one coming from just past the barrier (either a mirror reflect or an inverted mirror reflect depending on the barrier) so that the two of them meet when the pulse gets to the barrier.

  1. Sketch what the two pulses would look like so that the superposition of the two pulses would give you what you see in the hard barrier case. 
  2. Sketch the same thing for the soft barrier case.

 

 

Original problem: Exploration 17.3, Physlet Physics by Christian and Belloni
Original credits: Illustration authored by Morten Brydensholt, Wolfgang Christian, and Mario Belloni.
Original credits: Script authored by Morten Brydensholt, Wolfgang Christian, and Mario Belloni.
2004 by Prentice-Hall, Inc. A Pearson Company