22 Common Science 



were arguing, and said that neither way would work ; that 

 although the hose was long enough, the water was too far 

 down to be raised in either way. He advised the boys to 

 find a bucket and to use the hose as a rope for lowering it. 

 Who was right ? 



Inference Exercise 



EXPLANATORY NOTE. In the inference exercises in this book, 

 there is a group of facts for you to explain. They can always be ex- 

 plained by one or more of the principles studied, like gravitation, water 

 seeking its own level, or air pressure. If asked to explain why sucking 

 through a straw makes soda water come up into your mouth, for in- 

 stance, you should not merely say "air pressure," but should tell why 

 you think it is air pressure that causes the liquid to rise through the 

 straw. The answer should be something like this: "The soda water 

 comes up into your mouth because the sucking takes the air pressure 

 away from the top of the soda water that is in the straw. This leaves 

 the air pressing down only on the surface of the soda water in the glass. 

 Therefore, the air pressure pushes the soda water up into the straw and 

 into your mouth where the pressure has been removed by sucking." 

 Sometimes, when you have shown that you understand the principles 

 very well, the teacher may let you take a short cut and just name the 

 principle, but this will be done only after you have proved by a number 

 of full answers that you thoroughly understand each principle named. 



Some of the following facts are accounted for by air pressure ; 

 some by water seeking its own level ; others by gravitation. See 

 if you can tell which of the three principles explains each fact : 



1. Rain falls from the clouds. 



2. After rain has soaked into the sides of mountains it runs 



underground and rises, at lower levels, in springs. 



3. When there are no springs near, people raise the water from 



underground with suction pumps. 



4. As fast as the water is pumped away from around the bottom 



of a pump, more water flows in to replace it. 



5. After you pump water up, it flows down into your pail from 



the spout of the pump. 



6. You can drink lemonade through a straw. 



7. If a lemon seed sticks to the bottom of your straw, the straw 



flattens out when you suck. 



8. When you pull your straw out to remove the seed, there is no 



hole left in the lemonade ; it closes right in after the straw. 



