Gravitation 



27 



FIG. 12. The upper tube is filled with water and the lower with oil. What will 

 happen when she pulls the cardboard out? 



If you are careful, you will not spill a drop. If nothing 

 happens when the cardboard is pulled away, gently rock the 

 two tubes, holding their mouths tightly together. 



Oil is lighter than water, as you know, because you 

 have seen a film of oil floating on water. When you 

 have the two test tubes in such a position that the oil 

 and water can change, the water is pulled down under the 

 kerosene because gravity is pulling harder on the water 

 than it is pulling on the kerosene. The water, there- 

 fore, goes to the bottom and this forces the kerosene up. 



Application 6. Three men were making a raft. For floats 

 they meant to use some air-tight galvanized iron cylinders. 

 One of them wanted to fill the cylinders with cork, " be- 

 cause," he said, " cork is what you put in life preservers and 

 it floats better than anything I know of." " They'd be 

 better with nothing in them at all," said a second. " Pump 



