The heat from the burner starts the molecules in contact with the burner start to move. Those molecules bump against others in the pot, which bump others, until all the molecules in the pot, including in the handle, are moving. When someone touches the pot handle, they feel the heat.
The heat has moved from the burner to the cook's hand through conduction. Conduction is an important way that heat travels in space, but only within a spacecraft. Since there is very little matter in deep space, heat cannot leave a spacecraft by conduction. Convection is a very important way that heat moves on Earth, but is not very important in space.
Convection happens when a substance that can flow, like water or air is heated in the presence of gravity. When air or water is in the presence of gravity, the gravity pulls all of it down. The bottom of the air or water becomes denser because it is pulled down and also pushed down by the weight of the molecules on top of it. When there is heat at the bottom of this air or water, the air or water molecules in contact with the heat start to move, and the molecules spread apart.
The heated air or water becomes less dense. How does heat conduction occur in the ceramic itself? The mechanism of heat transfer through the bulk of the ceramic mug is described in a similar manner as it before. The ceramic mug consists of a collection of orderly arranged wigglers. These are particles that wiggle about a fixed position.
As the ceramic particles at the boundary between the hot coffee and the mug warm up, they attain a kinetic energy that is much higher than their neighbors. As they wiggle more vigorously, they bang into their neighbors and increase their vibrational kinetic energy. These particles in turn begin to wiggle more vigorously and their collisions with their neighbors increase their vibrational kinetic energy.
The process of energy transfer by means of the little bangers continues from the particles at the inside of the mug in contact with the coffee particles to the outside of the mug in contact with the surrounding air.
Soon the entire coffee mug is warm and your hand feels it. This mechanism of conduction by particle-to-particle interaction is very common in ceramic materials such as a coffee mug. Does it work the same in metal objects? For instance, you likely have noticed the high temperatures attained by the metal handle of a skillet when placed upon a stovetop. The burners on the stove transfer heat to the metal skillet.
If the handle of the skillet is metallic, it too attains a high temperature, certainly high enough to cause a bad burn. The transfer of heat from the skillet to the skillet handle occurs by conduction. But in metals, the conduction mechanism is slightly more complicated.
In a manner similar to electrical conductivity, thermal conductivity in metals occurs by the movement of free electrons. Outer shell electrons of metal atoms are shared among atoms and are free to move throughout the bulk of the metal. These electrons carry the energy from the skillet to the skillet handle. The details of this mechanism of thermal conduction in metals are considerably more complex than the discussion given here. The main point to grasp is that heat transfer through metals occurs without any movement of atoms from the skillet to the skillet handle.
This qualifies the heat transfer as being categorized as thermal conduction. Is conduction the only means of heat transfer? Can heat be transferred through the bulk of an object in methods other than conduction? The answer is yes. The model of heat transfer through the ceramic coffee mug and the metal skillet involved conduction. The ceramic of the coffee mug and the metal of the skillet are both solids. Heat transfer through solids occurs by conduction.
This is primarily due to the fact that solids have orderly arrangements of particles that are fixed in place. Liquids and gases are not very good conductors of heat. In fact, they are considered good thermal insulators. Heat typically does not flow through liquids and gases by means of conduction. Liquids and gases are fluids; their particles are not fixed in place; they move about the bulk of the sample of matter. The model used for explaining heat transfer through the bulk of liquids and gases involves convection.
Convection is the process of heat transfer from one location to the next by the movement of fluids. The moving fluid carries energy with it. The fluid flows from a high temperature location to a low temperature location. To understand convection in fluids, let's consider the heat transfer through the water that is being heated in a pot on a stove.
Of course the source of the heat is the stove burner. The metal pot that holds the water is heated by the stove burner. As the metal becomes hot, it begins to conduct heat to the water. The water at the boundary with the metal pan becomes hot. Fluids expand when heated and become less dense. So as the water at the bottom of the pot becomes hot, its density decreases. Differences in water density between the bottom of the pot and the top of the pot results in the gradual formation of circulation currents.
Hot water begins to rise to the top of the pot displacing the colder water that was originally there. And the colder water that was present at the top of the pot moves towards the bottom of the pot where it is heated and begins to rise. These circulation currents slowly develop over time, providing the pathway for heated water to transfer energy from the bottom of the pot to the surface.
Convection also explains how an electric heater placed on the floor of a cold room warms up the air in the room. Air present near the coils of the heater warm up. As the air warms up, it expands, becomes less dense and begins to rise. As the hot air rises, it pushes some of the cold air near the top of the room out of the way.
The cold air moves towards the bottom of the room to replace the hot air that has risen. As they spread further apart, they push against the detergent film and form a bubble. When the bottle is then placed in cold water, the gas molecules slow down and the bubble shrinks. Heat- Energy on the Move. Here's what to do:. Place some ice in a large cup and add water to make ice water. At the same time, you and your adult partner should put one drop of yellow and one drop of blue food coloring on the surface of the hot and cold water.
What do you notice about the way the food coloring moves in the two cups? Convection occurs when a material is free to move, such as a liquid or a gas. Again, consider a pan on the stove.
Put water in the pan, then turn on the heat. As the pan gets hot, some of that heat transfers to the molecules of water sitting on the bottom of the pan via conduction. That speeds up the motion of those water molecules — they are warming. As the water warms, it now begins to expand. That makes it less dense. It rises above denser water, carrying away heat from the bottom of the pan. Cooler water flows down to take its place next to the hot bottom of the pan.
As this water warms, it expands and rises, ferrying its newly-gained energy with it. In short order, a circular flow of rising warm water and falling cooler water sets up. This circular pattern of heat transfer is known as convection. Large birds such as frigate birds and human flyers riding engineless gliders often ride these thermals — rising blobs of air — to gain altitude without using any energy of their own.
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