Why is the bond market so sensitive to interest rates? What is the mathematics behind this relationship? Do a Google search to find a corporate bond issue where the company has either defaulted on the payments or called back the bonds.

What was the reason(s) for the company to either default on payments or call back the bonds? How would you compare the investment in bonds vs. stocks? Which one would you prefer? Is it a good strategy to have a combination of stocks and bonds in your portfolio?