Bond Traders/Investors... I have a question for you.

[Soultrader]

For any bond investors/traders, I would like to ask a few questions. Fixed income is still relatively new to me but I am learning it gradually. I have a question regarding bond trading methods. If one is bullish on the market and expects interest rates to fall in the future, a roll-over from short-term bonds to medium and long-term bonds, is said to be advantageous. Can anyone help me understand this concept? Also, why do longer-term bonds have greater price movements?

Also regarding the affect of foreign exchange and overseas interest rates, how does an appreciation in yen increase the demand for Japanese bonds?

Thanks.