CONTENTS 



CHAPTER 



i. GRAVITATION 



1. A real place where things weigh nothing and 



where there is no up or down . . . i 



2. "Water seeks its own level" . . .6 



3. The sea of compressed air in which we live : 



Air pressure . . . . . .10 



4. Sinking and floating : Displacement . . 23 



5. How things are kept from toppling over: 



Stability . . . . . . 29 



2. MOLECULAR ATTRACTION . . . ,* 36 



6. How liquids are absorbed: Capillary at- 



traction ..... . 36 



7. How things stick to one another : Adhesion 41 



8. The force that makes a thing hold together : 



Cohesion ...... 44 



9. Friction ....... 49 



3. CONSERVATION OF ENERGY ..... 57 



10. Levers ....... 57 



11. Inertia ....... 66 



12. Centrifugal force ..... 72 



13. Action and reaction . . . . 77 



14. Elasticity ....... 82 



4. HEAT ......... 88 



15. Heat makes things expand .... 88 

 1 6. Cooling from expansion .... 94 

 17. Freezing and melting . . . . * 96 

 1 8. Evaporation ..... g| 100 



19. Boiling and condensing . . . 107 



20. Conduction of heat and convection . . 116 



