HeatTransfer

1、Heat TransferMarch 20, 20071Warm-upWrap a fur coat around a thermometer. Will its temperature rise? Explain why or why not.If you hold one end of a metal nail against a piece of ice, the end in your hand soon becomes cold. Does cold flow from the ice to your hand? Explain.2AnswerNo, the thermometer

2、will not heat up because it is the same temperature as the coat. There has to be a difference in temperature in order for heat transfer to take placeNo, cold does not flow. Heat flows from your hand to the nail to the ice. Since your hand is losing heat, it feels cold. HEAT is the only thing that fl

3、ows.3Practice QuestionExplain why “firewalkers” can walk safely across a bed of red-hot coals in bare feet. 4AnswerBecause the rate of heat transfer is slow, because coals are not very good conductors. If they walk fast enough, there is only a small amount of heat transferred to their feet, and they

4、 do not burn.5Practice QuestionIf heat transfers from hot to cold, and stops when the two objects reach the same temperature, explain why it is possible for the inside of your car to be hotter than the air outside on a hot summer day.6AnswerThe greenhouse effect. Electromagnetic waves from the sun e

5、nter your car through the windows and are absorbed by the seats and other objects in the car. They then re-emit electromagnetic radiation of a different wavelength that cannot pass through glass. All of that energy is therefore trapped inside the car, causing the temperature to rise.7Practice Questi

6、onSince a hot cup of tea cools more rapidly than a lukewarm cup of tea, would it be correct to say that a hot cup of tea will cool to room temperature before a lukewarm cup of tea will?8AnswerNo, because as it cools, the rate of heat transfer slows down until it is just as slow as the lukewarm cup o

7、f tea. The only way to make it cool faster is by introducing convection. (mpemba effect)9Practice QuestionThe Concorde supersonic airplane is 20 cm longer when in flight. Explain why.10AnswerAs the jet flies, it experiences a huge amount of friction, which heats it up significantly. This causes ther

8、mal expansion, and the plane lengthens.11Practice QuestionWhat is temperature a measure of?12AnswerThe average kinetic energy of the particles.13Practice ProblemIf you drop a hot rock into a pail of water, the temperature of the rock and the water will change until both are equal. The rock will cool

9、 and the water will warm. Is this true if the rock is dropped into the Atlantic Ocean?14AnswerYes, yes, yes! Even though the Atlantic ocean is huge, the heat that leaves the rock enters the water (law of conservation of energy). This means that the temperature will increase. Since the ocean is a hug

10、e body of water, it will be an incredibly small change, but a change nonetheless.15Practice ProblemWhen you step out of a swimming pool on a hot, dry day, you feel quite chilly. Why?16Practice problemThe water will start evaporating in the air. Evaporation requires energy (heat) and that heat will c

11、ome from your body. Since you are losing heat, you will feel cold.17Practice ProblemDoes a gas give off or absorb energy when it turns into a solid?18Answer:It gives off energy, because it is going from high energy to low energy.19Practice ProblemWhy does blowing over hot soup cool the soup?20Answer

12、Convection cooling is a very effective method of heat transfer.21Practice ProblemIn a still room, smoke will sometimes rise only so far, never reaching the ceiling. Why?22AnswerThe smoke will be initially hot. Since hot air is less dense than cool air it will rise. However, it will cool as it rises until its density is the same as the density of the air in the room. At that point, it will stop rising.23QuestionIf a cool cup of water is floated inside of a pot of water that is already boiling, will the water in the cup ever boil?24AnswerNO! Heat will transfer from the boiling water to the cool