Heat And Temperature (1969)

[Music] how much heat will this space heater give off in an hour how much heat will this air conditioner absorb in an hour how much heat is released in the human body when a person eats a piece of chocolate cake how much heat is released by this oil when it burns can you answer these questions well first you have to know what heat is what comes to your mind when you think of heat fire boiling water is heat the energy in boiling water no the energy in the boiling water is called internal energy scientists define heat as the energy transferred from one material to another as from this hot plate to the boiling water before or after the energy transfer has taken place and the energy is in a material it is referred to as internal energy not heat the internal energy of the boiling water becomes heat again when it is transferred to an ice cube heat is defined as energy transferred from a hotter material to a colder material because of the difference in their temperatures to learn more about energy transfer and the measurement of heat let's do a demonstration with some boiling water at 212 degrees fahrenheit some ice water at about 38 degrees fahrenheit and a small quantity of liquid mercury at room temperature we'll start by placing the hot thermometer from the boiling water into the pool of mercury the temperature of the hot thermometer is falling that's as expected but what else is happening the thermometer that was in the mercury is showing a rise in temperature energy is being transferred from the hot thermometer that was in the boiling water to the cool mercury the two thermometers give a quantitative indication of energy transfer in the form of heat let's continue the demonstration with the very cold thermometer from the ice water the temperature of this thermometer is going up is the temperature of the thermometer in the mercury changing once again yes this time it's going down energy from the mercury is being transferred to the thermometer that was in the ice water the rise in temperature of the ice water thermometer is a quantitative indication of heat being absorbed does this mean that a thermometer can measure heat or are there other factors to consider to find out we'll do some experiments with equal amounts of heat we'll use one ounce brass weights at 200 degrees fahrenheit let's see what happens when we place one of the weights in two ounces of water and another of the weights in eight ounces of water we started with both samples of water at 70 degrees fahrenheit the temperature of the two ounces of water has gone up about six degrees the temperature of the eight ounces of water has gone up only about two degrees the internal energies of the two weights have decreased by almost equal amounts the energy transferred from each weight produces a quite different temperature change depending on the quantity of water being heated so the quantity of material must be considered to arrive at a measure of heat to see if there are other factors we'll do the experiment again this time we'll use the same quantities of liquid but different kinds there are two ounces of water in this beaker and two ounces of oil in this one once again both systems are at 70 degrees at the start will the temperature increases be the same when the systems absorb equal amounts of heat as before the temperature of the water has gone up about six degrees but the temperature of the oil has gone up about nine degrees this indicates that some materials get hotter than others even though they absorb approximately the same amount of heat so the kind of material must also be considered in arriving at a measure of heat still another factor which must be considered can be determined with two ounces of ice at 32 degrees and two ounces of water also at 32 degrees once again we'll transfer an equal amount of energy from each weight to the water and to the ice the water temperature has gone up about nine degrees the temperature of the ice however is still 32 degrees fahrenheit so there has been no temperature change even though heat was absorbed in this case however some of the ice has melted the transfer of energy has changed the state of some of the water from solid to liquid but it has not raised the temperature so changes of state of the material whether solid liquid or gas are a third factor to consider in arriving at a measure of heat let us measure out equal quantities of test material of the same kind in the same state will the change in temperature be a reliable measure of the heat absorbed or given off by the test material let's see both temperatures have gone up the same amount under these conditions we have a reliable measure of heat suppose we varied the amount of heat absorbed by the test material we could supply any amount of heat so long as we supply the same amount to each beaker the temperature changes are equal in every case the temperature change is directly related to the amount of energy transferred when the quantity kind and state of the test material are kept the same standard units of heat are defined in terms of the conditions we have seen the standard unit of heat in the english system is the british thermal unit the btu this is the amount of heat required to raise the temperature of one pound of water one degree fahrenheit the standard unit of heat in the metric system is the kilocalorie or large calorie this is the amount of heat required to raise the temperature of one liter of water one degree celsius or centigrade now we can answer the question we raised about how fast the space heater will give off heat to a room it's rated at 35 000 btus per hour it means that the heater can release enough energy in one hour to heat thirty five thousand pounds of water one degree fahrenheit or one thousand pounds of water thirty five degrees fahrenheit in the same manner we can answer the question about how fast the air conditioner will absorb heat from a room it's rated at 16 000 btus per hour this means that the air conditioner can absorb enough energy in one hour to cool sixteen thousand pounds of water one degree fahrenheit or one thousand pounds of water 16 degrees fahrenheit what about the piece of cake how do we know how much heat a piece of food can release when it oxidizes in the body we can find off by burning a sample of the cake in a calorimeter a known quantity of the cake is placed into a pan below an electric filament which will later be used to ignite the cake the pan and filament are lowered into a flask which can be sealed air tight pure oxygen is lead into the flask so that when an electric current is passed through the filament it will set the cake on fire the flask is then lowered into the outer chamber of the calorimeter containing a known quantity of water once the calorimeter is sealed a thermometer is lowered into the water now the cake is ignited on the basis of the temperature rise of the water it will be possible to calculate how much heat has been released by the burning cake the same method can be used in determining the heat output of other burning materials knowing the relationship between change in temperature and energy transfer a scientist can measure the btus given off by a sample of burning oil the calories given off by an electric coil the kilocalories absorbed by boiling water these are all examples of energy transfer in the form of heat [Music] you