What is the difference between conduction, convection, and radiation? The difference is that they are three different ways of transferring heat energy.
I think we first need to look at what heat is. Heat is defined as “the transfer of thermal energy from one physical system to another system, or from one region in a physical system to another region”. Heat is form of energy, known as thermal energy. Unless it is stored in some way, heat is always in transit between areas of high heat and areas of low heat. This is all because of the second law of thermodynamics, which is the rule of entropy. Systems always become more disordered because statistically there are far more ways a disordered system can exist than there are ways an ordered system can exist. This applies to heat as well. Heat will always move from a hot object to a cold object. Put a hot cup of coffee on the table and the heat energy will move to the air, equalizing the temperature. Put a cold glass of ice coffee on the table and the heat will move from the air into the glass, equalizing the temperature. This is because atoms don’t want to have more energy than they are supposed to and if they have extra energy in the form of thermal energy, they want to get rid of it as quickly as possible. Thermal energy is a form of kinetic energy and it refers to how much the molecules within a substance are moving. The more heat they have, the more they move. Energy has to go into the system to make them move. Once there is no more energy going into the system, they want to return to their original state and they release the energy, slowing down. The molecules in the coffee cup release their energy to the air and the coffee cup molecules slow down and the air molecules slightly speed up, until they are all moving at the same speed, or at the same temperature. There are three ways that an object can lose its heat energy and those are conduction, convection, and radiation.
Conduction is probably the form of heat transfer we are most familiar with and it involves heat transfer through touch. The objects undergoing the heat transfer have to be solid or a fluid that is stationary. When we heat an object, we supply it with energy and the molecules start to move faster, giving them more kinetic energy. If these high energy molecules come into contact with the molecules of another object, they can pass their energy across to those other molecules. By doing this, the molecules of the first object lose their thermal energy and the objects of the second object gain thermal energy. This happens until the two are equal. You can imagine it as holding a frying pan with a metal handle. As you supply energy from your gas hob, the molecules in the frying pan start to move more. If you touch the metal handle with your hand, the moving molecules in the frying pan will excite the molecules in your hand, giving them more energy and giving you a nasty burn. This is conduction.
Convection is a form of heat transfer in a fluid. It is where heat energy is moved from a high energy part of the fluid to a low energy part of the fluid. The high energy moves to the low energy, and the two equalize. This happens until all of the heat energy in the fluid is the same. A good example of this is a bath. If you are in the bath and the temperature is getting cold, you switch the hot tap on. You can feel the hot water by your feet, so you use your hands to stir the water. The high energy water by the tap moves to the low energy area by your upper body and imparts its energy. If you continue imputing energy from the tap, you can keep convecting the thermal energy until the whole bath is the same temperature.
The last type of heat transfer is radiation. Radiation is when the heat is transferred by electromagnetic waves that are produced by the heat. When the molecules in an object move because of the heat energy supplied to them, they collide with other particles. Every time they hit another particle, their kinetic energy is slightly reduced and this difference in energy is released as heat radiation. It is infrared radiation. This electromagnetic wave can travel and transfer that heat energy to something else.
When you are in a bath and the water is going cold, that is because of conduction, convection, and radiation. The heat is being conducted out of the water into the surrounding bathtub, the air, and your body. The heat is being convected out as currents swirl in the bath and bring the warm water to the top. And the heat is being radiated out as well. And this is what I learned today.
Sources
https://testbook.com/physics/difference-between-conduction-convection-and-radiation
https://byjus.com/physics/difference-between-conduction-convection-and-radiation
https://www.techtarget.com/whatis/definition/heat
https://en.wikipedia.org/wiki/Heat
https://byjus.com/physics/heat-transfer-thermal-radiation
Photo by Anastasia Shuraeva: https://www.pexels.com/photo/coffee-cup-and-glasses-on-a-table-4100824/