1. Chapter 20: Gases
How different from liquids? Many times they are invisible – therefore forgotten.

2. Atmosphere – lots of gas
How much air do we have?
Just 30 km!!!!!!
Gravity keeps air molecules close to the Earth
Air molecules are energized by Sunlight – keeps them off the ground

3. Can You Feel the Pressure
Gases are fluids too
Archimedes principle works!!!!
Floating, sinking, suspended
Difference – we are at bottom of the ‘ocean’ of air
Blimps – hot air balloons – Dirigibles – this is how helium works

4. Can You Feel the Pressure II
Difference – gases are compressible – air is surface thin at great height
Pressure difference is greater than liquids because density is different
Pike’s Peak bottle 10N/cm2 or 14 lb/inch2 – get steel pressure bar

5. Difference in Pressure
NATURE DOESN’T SUCK!!!!
Examples
Scuba Diving
Drinking from a straw
Vacuum cleaner
‘Suction’ Cups
Scuba bubbles – the bends
Extra credit project – tallest straw – how you made it – bring it in
NEITHER DOES PHYSICS!!!!!!!!!!!

6. Measuring Pressure
Barometers used to measure
Pressure
Elevation

7. Barometer
Two Types
Simple Barometer – Glass tube fills as air pressure increases

8. Other Barometer Two Types
Aneroid Barometer – Uses Pressure difference between inside and outside

9. Don’t Break the Law Boyle’s Law Uses of pressure
Pressure x Volume is constant at constant temperature
Pressure is proportional to density
- tires
Uses of pressure
Building bridges/subways

10. Let’s Be Flamboyant Buoyancy of air works like liquids
An object surrounded by air is buoyed up by a force equal to the weight of the air it displaces

11. Next Time Question 20-1
Consider an air filled balloon weighted so that it is on the verge of sinking – That is, its overall density just equals that of water. Now if you push it beneath the surface, it will
Sink
Return to the surface
Stay at the depth to which it is pushed

12. Still Air Molecules move randomly Brownian Motion
Same pressure in all directions

13. It’s the Principle Bernoulli’s Principle
when fluid is confined – speed increases
when speed of fluid increases - pressure drops
Water hose
Water out of a hose – put finger over it to increase the pressure

14. Exotic uses of Bernoulli
Lift of an object occurs when PressureAbove < PressureBelow
Airplanes – Use bernoulli …
But also use Newton’s 3rd law
2 ways plane flies

15. FAST CARS Formula 1 cars need wings!! …to keep them on the ground
Upside down wings
Upside down to keep on road 100mph can drive upside down, pass in tunnel?

16. Every Day examples of Bernoulli
Birds
Tornados/Hurricanes & houses
Baseball pitches
Umbrellas
Shower curtain
2 ways plane flies