PROPERTIES OF MATTER 



Experiment 7. Hold a bottle, mouth downward, over watei 

 and push it downward (Fig. 4). Compare the height of the watei 

 in the bottle with that around it outside. Give a reason for this 

 difference. Now tip the bottle side wise, as in Fig. 5, and note all 

 that happens. What takes place now that did not occur when 



FIG. 4 



FIG. 5 



the bottle was held in the other position ? How do you explain 

 the difference ? 



It is hard to fill a small-mouthed bottle with a thick liquid 

 like oil or molasses, because of the bubbles of air which' must 

 escape as the liquid enters. 



14. Cohesion. Cohesion is the force which holds the 

 molecules of a body together. This is a property common 

 to solids and liquids ; the molecules of gases, we have 

 learned, do not cohere, and therefore are free to become 

 widely separated. The greater the cohesive force between 

 the molecules of a substance, the more the substance 

 resists being broken or pulled apart. When cohesion is 

 great, a body is said to be tough. 



Experiment 8. Try to break pieces of different substances, 

 e.g. wood, glass, leather, bone, steel wire (knitting needles), iron 

 wire, copper wire, etc. Make a list of these in the order of their 

 cohesive force. 



Experiment 9 Hold a drop of water on a glass rod. Is 

 there anything about this to show that the molecules of water 

 cohere ? 



