Heat versus temperature. Heat is energy transferred from one body or system to another, due to thermal contact and that just means contact between two things, where the temperature is going to change and that is because energy is being transferred between the two objects.
The transfer of heat into energy from hotter to cooler objects is accomplished in three different ways. It’s accomplished by conduction, convection, and radiation.
The next lesson: Magnetic Field Part I, both lessons are included in Practice Tests.[divider]The following transcript is provided for your convenience.[divider]
Conduction is the direct transfer of heat from one substance to another, so the two substances or objects must be touching, it’s a direct transfer. Examples would include, ice melting in your hand, you’re hand is touching the ice in transferring its heat energy, making the ice melt. Another example would be burning your hand on a hot pot. If this pot was on the stove, it gained heat energy from the stove and then if you touched it without any kind of protection on, your hand would be burnt, as that hot heat was transferred to your hand and it was too much for your hand to handle. Those were results of direct contact.
Another way that heat energy is transferred is through convection and convection is the movement of matter due to density differences caused by temperature variations. This is usually related to heat transfer through liquids and gases, so that’s going to mean that if you have a warmer liquid or gas, it’s usually going to be less dense and rise up. If you have a cooler liquid or gas, it’s usually going to be more dense and it’s going to sink down, so warm air or gas or liquid is going to rise up. Cool is going to sink down and that’s because cooler objects, cooler liquids, and gases are going to be more dense and sink.
Warmer liquids and gases are going to rise up, they’re going to be less dense. Examples of that happening are the greenhouse effect, the gases moving around and that in close space are going to move the warm air around and keep the whole area enclosed in glass warm. Even though it’s only the sun that’s kind of heating things up close to the glass, the warm air is going to circulate.
Another example is how you’ve got warmer water on top in swimming pools and lakes and that’s because cooler water is going to sink down, warmer water is going to rise to the top. Now the sun is going to have some affect on warming up that water, but if you were to get in the pool at night without the sun being there, the warmer water is going to be on top and the cooler water is going to be at the bottom and that’s because that cooler water is denser and it’s going to sink.
If you get into a pool or lake, every once in a while, you might find a cold spot with your feet, because you feet are going to be touching deeper down where the cooler water is sunk down, because it’s denser and that’s an example of conduction. Similarly having warmer upper stories in a building in your home and an apartment and cooler lower stories. If you live on the first floor of a building its often going to be cooler, because all the cool air is going to rise or it’s going to sink down to your floor of the building and if you live on the very top floor, it’s often going to be warmer, because everyone’s warm air is rising up to the top, plus you’re getting hit with the sun without as much insulation.
Convection has to do with temperature difference, causing difference in density and that causing air or liquids to circulate, always with the cool sinking to the bottom and the warm rising to the top. The last way that heat energy is transferred is through radiation and radiation is the transfer of energy through empty space as electromagnetic waves and the examples we have of that, will kind of explain what the means. The sun is an example of that.
You can feel the heat from the sun, but you can’t see anything coming towards you. You don’t feel something touch you. There is no direct contact, it’s not about the air moving, it’s about the sun’s electromagnetic waves sending that radiation down and you feel this heat.
Another example would be with the light bull; if you put your hand near a light bulb it’s going to be hot. If you don’t touch it, you’re still not having direct contact but you can feel the heat around the edge of that light bulb and you can’t see it moving the air around. It’s not moving anything around that way, it’s just that the light itself is creating heat and it’s sending out heat in the form of radiation.
Another example would be a campfire, same thing. The flames are creating heat, you don’t have touch the flames directly to get the warmth. You can just feel it because it just moves through the air. Now there is some conduction involved with that as well and with a lot of these things, they can kind of work together to transfer heat. But just to give you examples of how each one is different, that’s what we’re trying to do here.
If you’ll notice with radiation a lot of the time it involves some kind of light as a heat source and that’s where your energy is being transferred from. Convection a lot of times is going to have to do with liquids and gases, and conduction has to do with the right contact. You also have to be touching whatever it is that you’re supposed to getting heat transferred from or that you’re supposed to be transferring heat too. That’s what heat is, the energy that’s transferred from one body or system to another and this is done usually, hotter to cooler and by conduction, convection, and radiation.
Now temperature is the measure of an object’s stored heat energy, so how much heat energy could this object give off if it touched something else or if it were to release some of its heat energy via convection or radiation. That’s what temperature is, it’s the measure of an objects heat energy that’s stored within it. When the temperature of an object goes up, its atoms move faster and that increases its kinetic energy.
Warmer items are going to have a higher temperature and therefore more heat energy stored within them, cooler items have a lower temperature and they’re going to have less heat energy stored within them. We use thermometers to measure temperature, so heat is energy transferred from one body to another. Temperature is the measurement of how much stored heat energy is in an object.
The next lesson: Magnetic Field Part I, both lessons are included in Practice Tests.