24 A YEAR IN SCIENCE 



a radiator or a register becomes heated and rises, as 

 the colder air above it sinks and in turn becomes 

 heated. In any room the air near the ceiling is warmer 

 than that near the floor. 



Convection due to displacement of molecules. In 

 liquids and gases the molecules in contact with the 

 source of heat are set in violent vibration. These 

 rapidly vibrating molecules rise and the cooler ones 

 then come in contact with the source of heat. This 

 process continues until the liquid or gas is uniformly 

 heated throughout. 



Questions 



1. Name three ways in which heat can be trans- 

 ferred from one substance to another. 



2. Give a definition for conduction. 



3. Name two good conductors of heat. Two poor 

 conductors. 



4. Do all metals conduct heat with equal rapidity? 



5. From your observation, how do solids, liquids, and 

 gases compare as conductors? 



6. If you place your hand on a piece of metal or 

 a piece of marble, does it feel warmer or colder than a 

 piece of wood of the same temperature? How do you 

 explain this ? 



7. Why are the pipes leading from a furnace 

 wrapped with asbestos? 



8. Why are stove pokers and flat irons usually pro- 

 vided with wooden handles? 



