Conduction, often called thermal conduction or heat conduction, is the transfer of heat through a temperature gradient. This conduction happens through microscopic particles diffusing and colliding under those temperature changes. In order for conduction to take place, two objects must be in contact with each other, either directly or indirectly. Conduction can occur in all states of matter: solid, liquid, gas, and plasma.
When conduction takes place, it is always a matter of heat moving from the hotter object to the colder, meaning when two objects are in contact with each other-one that is hot and one that is cold-the heat will always transfer to make the other object hotter, not the other way around.
1. Automobile engine:
When a car is started on a cold day, it's a good idea to let the engine heat up before trying to drive. This heat helps the fluids in the engine become more liquid, and helps components like the fan and drive belts be more malleable and less prone to snapping. After the engine has run for a few minutes, the hood of the car will feel warmer to the touch. Any frost or snow on the hood may begin to melt. This is an example of conduction as the heat generated in the engine fills the compartment that houses it; the metal components that hold the engine in place have also heated up due to direct contact with the heat source. The entire hood compartment becomes warmer due to the conduction of heat through metal contact and air temperature inside the hood.
2. Roasting marshmallows
When cooking marshmallows over a campfire, many people use a long wooden stick to hold the marshmallow close to the flames or embers. In a pinch, though, a metal coat hanger that has been straightened out will do the job. However, be prepared for that end of the coat hanger to become hot to the touch. When the metal end of the hanger that holds the marshmallow begins to heat up due to contact with either the flames or the heat generated by the fire, the temperature of the metal hanger will increase. The temperature gradient will change as heat travels from the flame end to the handle end of the hanger.
3. Picking Up a Coin
On a cold day, a coin on the ground will become very cold due to its contact with the concrete or asphalt. The surrounding air temperature will also make the coin colder. If someone picks up that coin. It will feel cold to the touch, perhaps shockingly cold, due to the difference in the person's body heat and the cold metal of the coin. After a moment or two, the coin will begin to get warmer in the person's hand as the body heat from the hand changes the temperature of the coin through direct contact.
4. Saving a Life with Body Heat
A person who is trapped outside in the extremely cold temperatures can suffer from frostbite, hypothermia, and cold-related organ shut down. This extremely dangerous situation can lead to death. When a person is rescued, the body much be reheated gradually but effectively. In a professional rescue situation, the victim is moved inside and covered in warming blankets, which are essentially fabric sheets with heat conducting coils inside. This contact with the heating elements increases the victim's body temperature slowly and allows blood to move to the organs and muscles once again. In the event that a professional rescue isn't available, two people can keep themselves warmer through body heat exchange, where heat from one person passes to the other colder person, and vice versa.