1 82 Common Science 



anything like the speed of light. In the time that it 

 takes sound to go a mile, light goes hundreds of thousands 

 of miles, easily coming all the way from the moon to 

 the earth. That is why we see the steam rise from the 

 whistle of a train or a boat before we hear the sound. 

 The sound and the light start together ; but the light 

 that shows us the steam is in our eyes almost at the 

 instant when the steam leaves the whistle; the sound 

 lags behind, and we hear it later. 



Application 42. Explain why a bell rung in a vacuum 

 makes no noise ; why the clicking of two stones under water 

 sounds louder if your head is under water, than the clicking 

 of the two stones in the air sounds if your head is in the air ; 

 why you hear a buzzing sound when a bee or a fly comes 

 near you ; how a phonograph can reproduce sounds. 



Inference Exercise 

 Explain the following : 



251. The paint on woodwork blisters when hot. 



252. You can screw a nut on a bolt very much tighter with a 



wrench than with your fingers. 



253. When a pipe is being repaired in the basement of a 



house, you can hear a scraping noise in the faucets 

 upstairs. 



254. Sunsets are unusually red after volcanic eruptions. 



255. Thunder shakes a house. 



256. Shooting stars are really stones flying through space. When 



they come near the earth, it pulls them swiftly down 

 through the air. Explain why they glow. 



257. At night it is difficult to see out through a closed window 



of a room in which a lamp is lighted. 



258. When there is a breeze you cannot see clear reflections in a 



lake. 



259. Rubbing with coarse sandpaper makes rough wood 



smooth. 



260. A bow is bent backward to make the arrow go forward. 



