10 LABORATORY EXERCISES 



iron is swinging freely, try to stop it by a sudden pull on the 

 thread. What happens? Why? 



Now stop the flatiron, attach the thread once more, and try 

 to set the iron to swinging by giving a sudden pull on the 

 thread. What happens? Why? 



d. Tie to a small ball a rubber band or cord, and (out of 

 doors, or where you cannot break a window) whirl the ball 

 slowly about your hand. What is the effect upon the rubber 

 as you whirl the ball mo"re and more rapidly? What does this 

 indicate as to the intensity of the force exerted on the ball as 

 the speed of the ball increases? 



e. Into a small pail put about a cupful of water, and whirl 

 the pail around rapidly in as large a circle as you can. Does 

 the water fall out when the pail is upside down? How is it possi- 

 ble for a car to "loop the loop"? 



EXERCISE 7 

 ADHESION OF LIQUIDS TO SOLIDS; LIQUID SURFACES 



Apparatus and Materials. Mercury, glass tube or rod, water, glass 

 or beaker, vaseline (or grease or machine oil), nail, silver spoon, pencil, 

 sheet of glass, iron stove lid or sheet of iron, graduated cylinder, needle, 

 bowl. 



a. Into a dish containing mercury dip a clean glass tube or 

 rod; then remove it. Does the mercury wet the glass? What 

 form has the surface of the mercury where the tube (or rod) 

 enters it? Make a drawing of it. Now dip the glass tube into 

 water. What is the form of the surface about the tube. Draw 

 this surface also. 



What is the shape of a water surface near the sides of a glass 

 dish? 



b. Thoroughly cover the inside of a water glass or beaker 

 with a thin layer of vaseline or lard; then partly fill the glass 



