two equally important questions: If work=forcexdistance, how does a galvanic cell do "work" if there is not force nor any distance travelled by the force. question 2: Friction is a NC force that increases internal energy. Right? Doesn't friction also cause heat? My physics book says: If no heat: mechanical energy= KE+PE+Internal Energy If no heat and no frictionME=PE+KE. How can you have friction without heat? Also can you tell me a brief description between q, deltaH, and U by the way if you saw this on another forum, it is because I asked it on another forum, but got a semi-incomplete answer. this is the answer I got for your reference: Imagine what happens to space shuttle when it's going back to Earth from orbit: molecules of space ship are colliding with air molecules (denser and denser with lower altitude). High velocity of vehicle + pretty normal velocity of air molecules (~343 m/s) results in heating space ship to 1650 C.. http://en.wikipedia.org/wiki/Space_Shuttle...otection_system [Broken] This is pretty extreme example. Any air molecules colliding with any body that has some velocity is resulting in taking part/all of kinetic energy from that body (or particle), which is resulting as acceleration of air molecules, and deceleration of body. Until both bodies have the same temperature. And the same happens when we slide some body, on another body like table. The only difference is scale.