Let’s begin with this instance. When we pour in water of 100OC into an aluminium cup whose temperature is the same as that of its surrounding; let’s say 22OC. We will observe the followings:
The temperature of water inside the aluminum cup will begin to decrease from its initial 100OC.
The temperature of the aluminium cup will increase from its previous 22OC.
After some period of time, the temperature of the aluminium cup, water and the surrounding will become the same.
Note: OC = degree centigrade which is a unit of temperature. For now, consider temperature to be the degree of hotness or coldness of a substance or an object with reference to some standard value.
From the above observations, it can be said that the heat present in the water molecules are first transferred to the aluminium cup and then to the surroundings. (Recall that aluminium is a metal and metals are good conductors of heat. You may read our article on physical properties of metals here.
Eventually, the system and the surroundings will reach the same temperature as the heat transfer ceases. It is at this point, that the water, aluminium cup and the surrounding are said to have reached thermal equilibrium. This is the concept of the Zeroth law of thermodynamics. Read the Zeroth Law of Thermodynamics here.
Note: Regardless of the fact that the surrounding receives heat from the water and aluminium cup, its temperature will remain approximately unchanged for the following reasons:
The volume of air in the surrounding is so large.
The water and aluminium will not continue to permanently give out heat energy to the surrounding.
Diffusion will continue to occur in the surrounding. You may wish to read our article on diffusion HERE.
Heat is never lost because it is a form of energy; rather it will be transferred according to the first law of thermodynamics which states that “energy can neither be created nor destroyed but can be transferred from one form to another”.
In fact, from our above instance, the transfer of energy (heat energy in this case) from the water to the aluminium cup to the surroundings is referred to as HEAT.
Heat can simply be said to be the transfer of energy from an object or substance or system with a higher temperature to another of a lower temperature.
Let consider another reverse example with regards to heat. Now, imagine that a cold bottle of water is brought out of the fridge into the kitchen. Assuming the temperature of the water is 3OC while that of the environment is 22OC, the followings will occur.
The temperature of the cold bottle of water will start to increase from its initial 3OC
The temperature of the bottle will begin to increase from its initial 3OC.
After some period of time, the temperature of the bottle, water and the kitchen surrounding will become the same.
Note: At no point did the coldness of the bottle or water escaped into the surrounding. Instead it is the temperature of the room that actually increased that of the bottle and water. In fact, if the temperature of the room was higher than 22OC, heat transfer will be achieved at a much more rapid rate (that is, the rate at which the temperature of the water and bottle increases will be faster).
Since heat energy is being transferred from the kitchen surrounding to the bottle and then into the water. We can also say that heat will always be transferred from a higher region to a lower region until equilibrium is attained.
Heat is never static. It is always transferred and thus; an object will increase its temperature by gaining heat energy from its surroundings while another object simultaneously (at the same time) decreases its temperature by losing its heat energy to the surroundings. For this reason, we may also define temperature as the measure of ability of an object or substance to transfer heat energy to another object or substance. The higher the temperature, the greater the ability of an object or substance to transfer heat. Conversely, the lower the temperature, the greater the tendency of an object to receive the transferred heat.
For heat to be transferred, we must have systems or objects or substances of varying temperatures.
Topics in PhysicsImportant Physics Concepts Fundamental and Derived units Zeroth Law of Thermodynamics Gravity explained with some fun facts Concept of Heat and Temperature Heat Transfer, Conduction, Convection and Radiation