Air Pressure & Winds
Review
What is Pressure?
What is Pressure?
• A force pushing against something
Pressure
• Where is the most pressure from the books?
• Where is the least pressure from the books?
Pressure
• Where is the most pressure from the books?
The person’s head is feeling most pressure.
• Where is the least pressure from the books?
The very top book has the least pressure.
Water Pressure
• We live at the TOP of oceans of water
• What happens to your ears when you dive down? Why?
Water Pressure
• We live at the TOP of oceans of water
• What happens to your ears when you dive down? Why?
As you swim down, the
water above you is
pressing down. Your body
is underneath the weight
of the heavy water above.
That’s pressure!
Deeper = more pressure.
Water vs. Air
• What is water made of?
• What is air made of?
• Does water have pressure?
• Does air have pressure?
Water vs. Air
• What is water made of?
• Molecules!
• What is air made of?
• Molecules!
• Does water have pressure?
• YES!
• Does air have pressure?
• YES!
“Ocean of Air”
• We live at the BOTTOM of an ocean of air.
• All of that air is pressing down on us.
• Where will the pressure be the most? Why?
• Where will it be the least? Why?
Density and Air Pressure
• Density = how tightly packed
the molecules are
• Which air is more dense? Why?
• Which air is less dense? Why?
A
B
Density and Air Pressure
• Density and air pressure are related
• More molecules = more density
• More density = more pressure
More dense
• More molecules = more pressure
More pressure
• Less molecules = less density
• Less density = less pressure
• Less molecules = less pressure
Less dense
Less pressure
Molecules in the atmosphere
• Where is the MOST pressure?
• Why?
• Where is the LEAST pressure?
• Why?
Altitude (Height) Changes Pressure
• The lower you are, the more
pressure
• Molecules are closer together
• More dense
• More molecules are pressing
on you
• The higher you are, the less
pressure
• Molecules are spread out
• Less dense
• Fewer molecules are pressing
on you
Temperature Changes Pressure
• What do you notice?
• Which is more dense?
• Why?
• Which has more pressure?
• Why?
• Which is less dense?
• Why
• Which has less pressure?
• Why?
COLD
AIR
WARM
AIR
Temperature Changes Air Pressure
• Cooler air is more dense
• Cooler air has higher pressure
• Warmer air is less dense
• Warmer air has lower pressure
COLD
AIR
WARM
AIR
Sea Breeze
• Where is the high pressure? Low pressure?
• Which way will the wind blow?
Sea Breeze
• Where is the high pressure? Low pressure?
• Which way will the wind blow?
H
L
Land Breeze
• Where is the high pressure? Low pressure?
• Which way will the wind blow?
Land Breeze
• Where is the high pressure? Low pressure?
• Which way will the wind blow?
L
H
Wind!
• Remember, wind is caused by temperature differences.
• Wind always blows from HIGH PRESSURE to LOW
PRESSURE
• Remember, COLD is HIGH PRESSURE
• Remember, WARM is LOW PRESSURE
• So wind always blows FROM the colder place TO the
warmer place
Consider this…
• Why do you ears “pop” when you go up the
mountain, or when you fly upward in an airplane?
Answer:
• As you gain altitude (go higher), the air pressure
gets lower.
• The air pressure is still higher inside your ears.
• Air moves from high pressure to low pressure.
• Air comes out of your ears (high pressure) into the
surrounding air (low pressure).
• This makes a pop!
Consider This
• Why do your ears start hurting when you come
back down the mountain, or fly downward in the
plane?
Answer:
• When you lose altitude (go lower), the air pressure
increases.
• The air pressure is lower in your ears and higher in
the surrounding air.
• Air moves from high pressure to low pressure.
• Air moves from the surrounding air into your ears
(high pressure into low pressure), adding more air
and making them hurt!