1. Palm trees feeling the push of the air from a hurricane wind A balloon is inflated from a CO2 canister; pressure is increasing as the balloon inflates

2. Force exerted when molecules collide with the walls of their container Link to Phet Atomic Level Definition of pressure:

3. INCREASES

4. ≈ 30 lbs/in 2 A car or truck tire is typically inflated to a pressure of 30 lbs/in 2 while a bicycle tire is has a pressure of approximately 60 lbs/in 2. How is it possible for the car tire to support a much larger weight at a lower pressure? (Weight = Force due to gravity) 60 lbs/in 2 Tim Duggan, professional bike racer, Fairview Alumni

6. Which is better for walking on snow?

7. Which shoes will cause more pain to their dance partner’s toes when at prom? (Assume the stomp on the toes by the heel of the shoe is accidental)

8. Force exerted by a column of air from the edge of the earth’s atmosphere to the earth’s surface

9. Vacuum of space = low pressureDeep sea diver = high pressure Our bodies are designed to operate within a very narrow range of pressures A styrofoam head at the surface, 520 m and 905 m. Your head would not do well at high pressures without a helmet

10. Expansion of Marshmallows in low pressure Compression of Styrofoam Cups Pressure differences can cause objects to expand or contract Cup at 1 atm pressure and same cup taken to a depth of 2900 meters underwater 1 atmvacuum

11. Explosion (Gases expanding outward)

12. BeforeAfte r Explosive: The High pressure force of expanding gases The pressures produced by powerful explosives can exceed 250,000 atmospheres

13. Implosion – objects being crushed when external pressure > internal pressure

14. Air = N 2 O 2 External Pressure = Internal Pressure Figure #1: Can with water and air open to atmosphere

15. Air = N 2 O 2 Notice : Air is pushed out; replaced by steam! External Pressure = Internal Pressure Figure #2: Heating water in can to steam; open to atmosphere Hot Plate

16. Air = N 2 O 2 External Pressure > > Internal Pressure Figure #2: Heating water in can to steam; open to atmosphere ICE BATH STEAM HAS CONDENSED TO LIQUID WATER LEAVING A VACUUM!

17. Link to train car crushing video Train crushing using steam

18. Is pressure on the mountain top the same as at sea level? How does the height of the air column above the land vary with the elevation of the land? How does atmospheric pressure vary with altitude?

19. How does the density of air molecules change with altitude? Note different forces pushing down on surface of mercury bath Atmospheric pressure varies with altitude: Higher elevation = lower pressure

20. Sea level1 atm 4 miles0.5 atm 10 miles0.2 atm

21. Link to balloon in a vacuumLink to balloon in a vacuum Hint: What is happening in this video? ANS: As Balloon Rises Atm pressure ↓ ; Pressure inside balloon has to decrease to match surrounding atmosphere. As Balloon volume ↑, Balloon pressure ↓ Why does a balloon that rises to high in the atmosphere pop?

22. Barometer – measures height of a column of mercury supported by atmospheric pressure

23. 1 atm = 760 mm Hg = 760 torr = 101.3 kpa Units of Pressure

24. Picture of Hg barometer approximately 3 feet high Picture of water barometer 34 feet tall (top is on the 3 rd floor) Why is mercury (which is very toxic) used instead of water for barometers? Mercury is 13.5 times more dense than water

25. Measuring pressure differences using a Manometer Equal pressure heights of liquids are equal Pressure Difference = Difference in heights of liquids video animation

26. Case #1: Gas Pressure = Atm Pressure Manometers – measuring the pressure of a trapped gas

27. Case #2: Gas Pressure < Atm Pressure Manometers – measuring the pressure of a trapped gas P gas = Patm – height difference

28. Case #3: Gas Pressure > Atm Pressure Manometers – measuring the pressure of a trapped P gas = Patm + height difference