What is Heat

What is Heat?
Consider a very hot mug of coffee on the countertop of your kitchen. For discussion
purposes, we will say that the cup of coffee has a temperature of 80°C and that the
surroundings (countertop, air in the kitchen, etc.) has a temperature of !°C. "hat do you
suppose will happen in this situation# $ suspect that you know that the cup of coffee will
gradually cool down over time. %t 80°C, you wouldn&t dare drink the coffee. 'ven the coffee
mug will likely (e too hot to touch. )ut over time, (oth the coffee mug and the coffee will
cool down. *oon it will (e at a drinka(le temperature. %nd if you resist the temptation to
drink the coffee, it will eventually reach room temperature. +he coffee cools from 80°C to
a(out !°C. *o what is happening over the course of time to cause the coffee to cool down#
+he answer to this ,uestion can (e (oth macroscopic and particulate in nature.
-n the macroscopic level, we would say that the coffee
and the mug are transferring heat to the surroundings.
+his transfer of heat occurs from the hot coffee and hot
mug to the surrounding air. +he fact that the coffee
lowers its temperature is a sign that the average kinetic
energy of its particles is decreasing. +he coffee is losing
energy. +he mug is also lowering its temperature. the
average kinetic energy of its particles is also
decreasing. +he mug is also losing energy. +he energy
that is lost (y the coffee and the mug is (eing transferred to the colder surroundings. "e refer
to this transfer of energy from the coffee and the mug to the surrounding air and countertop as
heat. $n this sense, heat is simply the transfer of energy from a hot o(/ect to a colder o(/ect.