what is a form of energy that is always transferred from a warmer substance to a cooler one?
Thermal or heat energy.
The form of energy that is always transferred from a warmer substance to a cooler one is called heat. Heat transfer occurs through three main mechanisms: conduction, convection, and radiation.
1. Conduction: Heat transfer by conduction occurs when two objects are in direct contact with each other. In this process, the kinetic energy of the particles in the warmer substance is transferred to the particles in the cooler substance through molecular collisions. For example, when you touch a hot iron, heat is transferred from the iron to your hand through conduction.
2. Convection: Convection is the transfer of heat through the movement of a fluid (liquid or gas). When a fluid is heated, it becomes less dense and rises, carrying the heat energy with it. As it rises, the fluid transfers its heat to the surrounding cooler substance, which then becomes heated and rises, continuing the process. This is how heat is transferred in a process like boiling water, where the hot water rises to the top and cooler water replaces it at the bottom.
3. Radiation: Radiation is the transfer of heat energy through electromagnetic waves. Unlike conduction and convection, radiation does not require a medium to propagate. Heat is radiated in the form of electromagnetic waves, such as infrared radiation. For example, when you feel the warmth of sunlight on your skin, you are experiencing heat transfer through radiation.
In summary, heat is the form of energy that always flows from a warmer substance to a cooler one, and it can be transferred through conduction, convection, and radiation.