Find bars with different characteristics and strike them such that they make sound and observe the relative frequencies of the different bars. A hardware store is a great place to find these types of things, just don’t damage them in the store and be prepared to get lots of strange looks. You could alternatively just find things around the house. Compare drastically different bars and record your observations in your assignment (pick differences that will create significantly different frequencies, low and high). Some examples might include a hollow bar and a solid bar; a short bar and a long bar; a thick bar and a thin bar; metal bar and a wood bar; you could explore how the way you hold it affects the frequency; etc. You should have at least 3 different comparisons and a quick observation of the results for each comparison (again, just make sure the frequencies produced are noticeably different when changing the parameter).