Atmospheric Pressure

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Atmospheric Pressure

• your name here
• University of Maine
• NSF GK-12 Sensors!

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What is Atmospheric Pressure?

• Air is a physical substance which has mass
• Any object with mass is influenced by gravity

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The Weight of Air Really Adds Up

• At sea level, the weight of air produces a force
  of about 14.7 pounds per square inch (psi)

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Simple Barometer

• Atmospheric pressure supports a column of mercury
• Units of atmospheric pressure?
• Inches of Mercury!

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Pressure Can Be a Powerful Force

• Time for a demonstration

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Why Does This Happen?

• Hint

Pressure inside can becomes very low
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Why Does This Happen?
14.7 lbs

• Hint

Pressure inside can becomes very low
14.7 lbs
14.7 lbs
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Why Does This Happen?

• Hint

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Why Does This Happen?

• Atmospheric pressure wins the battle
• The thin walls of the can cant handle that kind
  of abuse (14.7 psi)

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Crushed Tanker Rail-Car
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For Next Week

• BE PREPARED TO EXPLAIN TO THE CLASS...
• What exactly caused the can to collapse
• What lowered the pressure in the can?

Some higher-level thinking is required
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Why Did the Soda Can Collapse?
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Why Did the Soda Can Collapse?

• Removed from heat

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Why Did the Soda Can Collapse?

• Inverted and quickly sealed using water

Soda Can Filled With Steam
Water
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Why Did the Soda Can Collapse?

• Steam condenses back to liquid water

Trapped Steam Condenses
Water
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Why Did the Soda Can Collapse?

• But why does the pressure inside the can drop so
  quickly???
• Steam occupies a much larger volume than liquid
  water

1 drop of water will fill a soda can with steam!
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Why Did the Soda Can Collapse?

• The can is truly empty (what we call a vacuum)

Nothing is in here!
Water
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Why Did the Soda Can Collapse?

• We know what happens next

Water