3. The pressure acting on the bottom of the suspended metal block is greater than that acting on the top due to the increase of pressure with depth.  The same is true with our atmosphere.  We are all submerged in our atmosphere.

4. The air is made up of molecules

5. Air molecules are everywhere.

6. The atoms in a liquid are closely packed while those in a gas are separated by much larger distances. Gases have a density ~ 1/1000 that of their liquid density

7. The density of a column of air decreases as altitude increases because air expands as pressure decreases. P 1 V 1 = P 2 V 2 Boyle’s Law

8. As a balloon rises, the weight of the atmosphere above it decreases, creating a reduction in the atmospheric pressure. Hence, the balloon expands. P 1 V 1 = P 2 V 2 Boyle’s Law

9. Like all matter, air molecules have mass.

10. Gravity pulls the air molecules toward the earth, giving them weight. The weight of the air molecules all around us results in what is called the air pressure.

11. Air pressure is equal in all directions. Pressure = force per unit area

12. High altitudes = lower pressure Low altitudes = higher pressure

13. As you go up in elevation Barometric pressure goes down. This is an inverse relationship.

14. Atmospheric Pressure vs. Altitude 120 110 100 80 70 60 50 40 30 20 10 90 0 -120-100-80-60-40-200204060 THERMOSPHERE Mesopause MESOPHERE Stratopause STRATOSPHERE Tropopause TROPOSPHERE Height above ground (kilometers) COLDERWARMER The atmosphere is divided into layers based on temperature.

15. to measure air pressure. A Barometer is used

16. In 1643, Evangelista Torricelli invented the barometer Maybe next I’ll invent spaghetti-flavored toothpaste!

17. Torricelli’s barometer used a glass column suspended in a bowl of mercury. The pressure caused by the weight of the air molecules pushed the mercury up into the glass tube. The weight of the mercury in the tube was equal to the weight of the air pressing down on the mercury in the dish.

18. As atmospheric pressure increases… The mercury in the tube rises.

19. Torricelli filled a tube with mercury and inverted it into an open container of mercury. Air pressure acting on the mercury in the dish can support a column of mercury 76 cm (760 mm) in height. How much does the atmosphere weigh? The same as 76 cm of mercury. 76cm mercury=1.013x10 5 Pascals Standard atmospheric pressure 34 feet of water or 14.7 lbs/in 2 (psi)

20. Pressure The normal force per unit area that a fluid exerts on the walls of its container, adjacent fluids or other boundaries. Units:N/m 2 = 1 Pascal –1 Bar = 10 5 Pa  typically about 1 atmosphere –1 atm = 1.013 x 10 5 Pa (101,325 Pa) –1 atm = 14.7 lb/in 2 –1 atm = 760 Torr (mm Hg) or 76 cm Hg

21. The Mercury Barometer Good:Bad: Simple to construct Simple to construct Highly accurate Highly accurate Glass tube is fragile Glass tube is fragile Mercury is very toxic! Mercury is very toxic! Not transportable. Not transportable. Is there a better way to measure air pressure?

22. The Aneroid Barometer!! No fragile tubes!No fragile tubes! No toxic chemicals!No toxic chemicals! No batteries!No batteries! Never needs winding!Never needs winding! Get yours today!!

23. An aneroid barometer uses a cell which has had most of the air removed. As the air pressure around the cell increases, it presses on the cell, which causes the needle to move. Television weather forecasters usually give barometric pressure in inches of mercury. However, meteorologists measure atmospheric pressure in millibars. MILLIBARS

24. Since pressure changes with altitude… …how does changing altitude affect a barometer?

25. Two types of barometric pressure measurements: Station pressure is the actual pressure at the recording location. It is affected by the local altitude. Sea level pressure is referenced to sea level, so it has the same altitude anywhere in the world.

26. Most aneroid barometers have a needle which can be set to remember the previous reading. Why would this be important?

27. Changing Pressure A rising barometer = increasing air pressure. This usually means:

28. Changing Pressure A falling barometer = decreasing air pressure. This usually means: Where’d the hula dancer go?

29. Otto Von Guericke Otto von Guericke built the first vacuum pump and created vacuums in various containers. He demonstrated the capacity of the atmosphere to do work and refuted the long-held notion that it was impossible for a vacuum to exist. Using hollow copper spheres about ½-meter in diameter, known as Magdeburg hemispheres, and an air pump of his own construction, Guericke demonstrated that a partial vacuum could be created by pumping much of the air out of the sphere. The air remaining in the sphere (at a pressure well below that of the atmosphere) was distributed evenly throughout the vessel.

30. Otto Von Guericke’s Magdeburg Experiment On 8 May 1654, Guericke, who was the mayor of Magdeburg, carried out his famous demonstration. In front of the Reichstag he demonstrated that several teams of horses (16 in all) could not pull apart two joined hemispheres when the air had been evacuated. By showing the muffling of a bell he proved that sound could not travel in a vacuum and also proved that combustion could not be supported in a vacuum by showing that a candle would extinguish.

31. Otto Von Guericke Using a piston in a cylinder, he also showed that when a vacuum was created on one side of the piston, the atmosphere would move the piston and a considerable mass through the distance, thus performing work. This was the basic principle of the Newcomen steam engine (1712), the first practical steam engine—used to pump water out of mines.

32. Atmospheric Pressure vs. Altitude 120 110 100 80 70 60 50 40 30 20 10 90 0 -120-100-80-60-40-200204060 THERMOSPHERE Mesopause MESOPHERE Stratopause STRATOSPHERE Tropopause TROPOSPHERE Height above ground (kilometers) COLDERWARMER The atmosphere is divided into layers based on temperature.