what is the direction of heat transfer

In the entire universe, it is natural for energy to move from one place to another. And unless there is human intervention, thermal energy – or heat – flows naturally in only one direction: from hot to cold. Heat moves naturally by any of the three means. These processes are called conduction, convection, and radiation. Sometimes more than one can happen at the same time. Read: what is the direction of heat transfer First, a little background information. All matter is made of atoms – single atoms or atoms linked in groups called molecules. These atoms and molecules are always in motion. If they have the same mass, then on average the hot atoms and molecules move faster than the cold atoms and molecules. Even when the atoms are locked in a solid, they oscillate back and forth around some mean position. In liquids, atoms and molecules are free to move from one place to another. In a gas, they have even more freedom of movement and will completely spread out in the volume in which they are trapped. Some of the easiest examples of heat flow occur in your kitchen. | Top Q&A Place the pan on the stove and turn on the heat. The metal on top of the burner will be the first part of the hot pan. The atoms at the bottom of the pan will begin to vibrate faster as they heat up. They also oscillate back and forth further than their average position. When they meet their neighbor, they share with that neighbor a part of their energy. (Consider this a very small version of a cue ball hitting other balls during billiards. The target balls, which were previously at rest, gain some of the cue ball’s energy and move.) collided with their warmer neighbors, the atoms began to move faster. In other words, they are warming up. These atoms, in turn, transfer some of their increased energy to neighbors even further away from the original heat source. This conduction of heat through solid metal is how the pan’s handle heats up even though it may not be near the heat source. Again, consider a pan on the stove. Put the water in the pan, then reduce the heat. When the pan heats up, some of that heat is transferred to the water molecules at the bottom of the pan through conduction. That speeds up the movement of those water molecules – they’re heating up.Lava lamp illustrates heat transfer through convection: Wax blobs warm at base and expand. This makes them less dense, so they rise to the top. There, they radiate heat, cool, and then sink to complete topqa.infoardojbp / iStockphoto As the water warms, it begins to expand. That makes it less dense. It rises above the denser water, taking away the heat from the bottom of the pan. The cooler water flows down to take its place next to the hot bottom of the pan. As the water warms, it expands and rises, taking the newly acquired energy with it. In brief order, a circular flow consisting of rising warm water and falling cold water forms. This form of circular heat transfer is called convection, and it is also the element that helps heat food in the oven. Air warmed by a heating element or gas flame at the top or bottom of the oven carries that heat to the central zone where the food lies. water in a pan on the stove. Large birds like peacocks (and non-motorized gliders) often ride these thermal wings – blobs of color in the air – to gain altitude without using any of their own energy. . In the ocean, convection caused by heating and cooling helps drive ocean currents. These currents move water around the globe. It can move through materials – or without them. This is radiation.Radiation, such as the electromagnetic energy emitted by the sun (seen here at two ultraviolet wavelengths) is the only type of energy transfer that operates on empty topqa.info visible light, a form of radiation. It goes through several types of glass and plastic. X-rays, another form of radiation, pass through flesh easily but are largely blocked by bone. Radio waves penetrate the walls of your home to reach the antenna on your stereo system. Infrared radiation, or heat, travels through the air from heaters and light bulbs. But unlike conduction and convection, radiation does not require matter to transmit its energy. Light, X-rays, infrared waves, and radio waves all reach Earth from distant regions of the universe. Those forms of radiation will pass through a lot of empty space along the way. X-rays, visible light, infrared radiation, and radio waves are all different forms of electromagnetic radiation. Each type of radiation falls into a specific wavelength range. Those types differ in the amount of energy they have. In general, the longer the wavelength, the lower the frequency of a particular type of radiation and the less energy it carries. The stove’s burner not only heats the pan, but also heats the air nearby and makes it less dense. That brings the warmth upwards through convection. But the burner also radiates heat in the form of infrared waves, causing nearby things to heat up. And if you’re using a cast iron pan to cook a delicious meal, be sure to grab the handle with a pothole: It’s going to be hot, thanks to conduction! Read more: You can’t eat anything with braces

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