Wednesday, August 31, 2011
Entrance Activity for 4.7
Conduction, Convection and Radiation1.What is the most common heat transfer mechanism in solids? Conduction
2.What is the most common heat transfer mechanism in liquids and gases? Convection
3.What is the only heat transfer mechanism in a vacuum? Radiation
4.Why can't conduction happen in a vacuum? Because conduction happened by the vibration of molecules which bump into each other and are passed through the bonds from particle to particle. There are no molecules in a vacuum.
5.What happens to the space between the molecules in a gas when you heat it? The space between the molecules increases (without the molecules itself increasing).
6.What happens to the density of a gas when you heat it? Density decreases.
7.Why can't convection happen in a solid? Because for convection to happen molecules must flow to create convection cycle. However, the molecules are packed together in solid and do not flow. (The particles' movement is restricted.)
Friday, August 19, 2011
4.6
4.610 June 201111:42·4.6 recall that energy transfer may take place by conduction, convection and radiationTask 1· Try the animation: particle model - conduction· Extension: what is the limitation of this animation? (Check your answer with the Heating a Solid animation)
We cannot control the amount/temperature of heat we would like it to be since the fire was lighted up by a match.
Task 2
· Try the quiz on the Cooking animation· Extension: what's the mistake in the description of convection?
The correct explanation should be that in a convection current, the molecules started to rise when heated, forcing the molecules on top to sink down to replace the risen molecules. The mistake is that they are not supposed shrink and sink just because they were cooled down.
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