Thermoynamics (from the Greek θερμη, therme, meaning "heat" and δυναμις, dunamis, meaning "power") is a branch of physics and of chemistry that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analysing the collective motion of their particles using statistics. Roughly, heat means "energy in transit" and dynamics relates to "movement"; thus, in essence thermodynamics studies the movement of energy and how energy instills movement. Historically, thermodynamics developed out of need to increase the efficiency of early steam engines.