transverse and longitudinal waves

[hacheemaster]

Advertisement - Members don't see this ad

This question is from BR physics Part V:
Question 37. The waves that can be generated in a long cylindrical steel rod are:
A. transverse waves only
B. longitudinal waves only
C. both transverse and longitudinal, depending on the source
D. No waves can be propagated through a solid.

I put B. However, BR says the answer is C, stating, "To generate transverse waves in a thin steel rod, hit it vertically. To generate longitudinal waves in the same rod, hit it horizontally, parallel to its length.

I am getting confused how the transverse waves can be generated in a steel rod.

..._____b____
a|__________| c
...........d
Let's suppose we have the steel rod above. If I strike the rod lengthwise, the the waves are longitudinal because they travel from point a to c. If I strike the rod horizontally, at point b, then they are still longitudinal because they travel from point b to d. Even if we feel the disturbance at c when we strike the rod at point b, it seems that the waves are still stretching and compressing in the direction of travel, which is simply changed from b->d to b->c.

Please help me understand how the wave propagates. I've tried looking at 2-d models in wikipedia but that didn't help 🙁 http://en.wikipedia.org/wiki/Longitudinal_wave.

 

[dragon529]

If you hit it vertically at b, it'll bounce toward d then bounce toward b. Repeat. Therefore, you can generate a transverse wave.

 

[hacheemaster]

if the wave propagates from b to d then it is still longitudinal because the medium, the rod is our case, is compressing and stretching in the direction the wave is traveling (b->d).