Fig. 35.—Air pressure keeps the water In the tumbler.
Fig. 36.—Cross-section of a modern drinking fountain.
Exercises
1. Do you think Archimedes' Principle applies to the air? Does Pascal's Law? Why?
2. Find the downward pressure of the mercury in a barometer tube if the cross-section is 1 sq. cm. and the height 75 cm. at the level of the mercury surface in contact with the air. (The density of mercury is 13.6 grams per cc.)
3. What is the weight of the air in a room if it is 10 × 8 × 4 meters?
4. What weight of air is in a room 10 × 15 × 10 ft.?
5. When smoke rises in a straight line from chimneys, is it an indication of a high or low barometric pressure? Why?
6. Why does a tumbler filled with water and inverted in a dish with its rim under water remain full?