Mantra vs Shloka

I happened to ask my father and Perippa(father's elder brother) the other day about the difference between Shlokas and Mantras in Hindu religion. The basic difference as I learned is that the essence of Mantras lies in "sound", in rhythmic chanting with varying emphasis that generates different energy levels in the body; whereas Shlokas are meant more for our well-being and peace of mind by reciting verses in praise of the Lord that inspire us towards goodness.

A more detailed explanation is here from my Perippa's e-mail:

Shloka is like a hymn offered as a prayer to God, mostly extolling glorious attributes of God, praying for our well-being. It is an ingenious technique of putting into practice Positive Thinking, as all shlokas talk about positive attributes. While we hear lot of lectures on Positive Thinking, seldom have they suggested the techniques to practice. No one is going to keep on repeating - "I want to think positive and practice". But by repeating shlokas, he reminds himself of good things. The meanings of Astothram (by which a priest does archana in a temple) are all nothing but good attributes of God which we need to imbibe. If you are asked to repeat them in raw form, you may not do so. But if you create an interesting model, like offering flowers to God chanting archance, you will do it with joy. Our tradition has conceived easy ways that can be practised by people of all walks of life, intellectual levels and of all ages.

Mantras are that which protects you by chanting it, protects your mind from negative thoughts.  Manana Thrayate Ithi Mantra. Sound by itself is all-powerful - it is the sounds that has manifested the universe, it is sound that will unmanifest the universe too. Mantras are the powerful carriers of cosmic energy. Rhythmic recitation of Mantras generate bioelectrical impulses in the neural system and sensitize the endocrine glands and activate specific neuro-harmonal secretions for a healthy body, creative mind and ESP. Vedas and Gayathri Mantram belong to this category. For instance, HariOm - the sound "Ha" activates solar plexus, "Ri" activates thyroid, and "Om" activates the brain.

Exceptions: Vishnu Sahasranamam and Lalitha Sahasranamam, though in the form of Shlokas, contain powerful syllables, the recitation of which have good effects on human body and mind.