Entropy
Definition 1 of 3
Pro Tip 1/3
Isolated Systems
Entropy increases in isolated systems where energy isn't added or lost. The universe is the ultimate isolated system, with entropy always increasing.
Pro Tip 2/3
Not Reversibility
High entropy means a system isn't easily returned to its prior state. Melting ice cubes show increasing entropy as they won't reform without energy.
Pro Tip 3/3
Order to Disorder
Entropy shows a system's transition from order to disorder. A neat room becomes disordered over time, demonstrating entropy.