Ideas aren't physical things in the same way energy is. When ideas are forgotten, they cease to be. The connections in the mind that make up an "idea" are used to form new information, and the idea is gone forever.
It is. There isn't really such thing as just "energy," though. It comes in many different forms. Kinetic, potential, nuclear, thermal, ionization, and so many more. From wikipedia:a property of objects which can be transferred to other objects or converted into different forms, but cannot be created or destroyed.[1] The "ability of a system to perform work"
Physical is generally accepted to mean "tangible," i.e., something which one is able to touch and feel - over physical as "part of physics." I agree, it's just - odd for me to see the word "physical" used to mean, more esoterically, "relating to or of physics." I'm sure both meanings are correct, but one is more common.