Which observations correctly describe the second law of thermodynamics? Check all that apply. Thermal energy that is not used to do work is often released to the surroundings. Thermal energy flows from a cooler object to a warmer object. Thermal energy flows from a warmer object to a cooler object. Thermal energy is released as unusable energy by a heat engine, which is never 100 percent efficient. Thermal energy flows when two objects in contact have a temperature difference.