2. Atmosphere
What have we discovered about air so
far?
– Is matter - has mass & occupies space
– Is mixture of gases - mostly nitrogen &
oxygen
– Made of individual nitrogen & oxygen
molecules flying through space
– Can heat up & cool down
– Gets denser as it cools, less dense as it
warms
3. Atmosphere
Planet Earth is completely surrounded
by a thin layer of air.
– Called the atmosphere
– Extends up about 300 miles above Earth’s
surface
– Most of the air is in first 9 miles
4. Investigating Air
Use syringe and plastic tube to find out
more about air.
Answer the following questions:
– What happens to air in the syringe when
you push and pull on the plunger?
– What can air do?
5. Air & Syringes
Record your observations on notebook
sheet
Try investigations on sheet - record
observations and any questions
What observations did you make?
What questions do you have?
6. Air Observations
When you clamp the tube closed and
push the plunger down, what happens to
the air?
Is there more air, less air, or the same
amount of air in the syringe when the air
is pushed into a smaller space?
– How do you know?
What happens when you let go of the
plunger after pushing it down?*
What do you think happens to the air
when it is pushed into a smaller space?
What happens to push the plunger back
out when you release the plunger?
7. Compression and Pressure
When you push on the plunger, the air
is forced into a smaller space.
– The air is compressed
– Same amount of air is still in the syringe
when compressed
Compressed air pushes back with a
force equal to the force compressing it.
– Pushing force is called pressure
– If force on plunger is released, the
pressure in the compressed air will push
the plunger out
8. Molecular Model of Air
Air is made of tiny particles
– Called molecules
– Made mostly of Nitrogen & Oxygen
molecules
– So tiny you can’t see them
– Free to move around - not attached
– Lots of space between molecules in
gases
9. Bottle Demonstration
What do you think will happen to the
bottle when I suck on the tube?
Why did the bottle get crumpled? What
caused the bottle to collapse?*
Bottle collapsed and crumpled for the
same reason a syringe plunger moves
in and out “by itself” when connected to
a second syringe.
What causes plunger in syringe #2 to
slide in and out when you push and
pull the plunger in the syringe #1?
10. Atmospheric Pressure
Syringe
has a little bit of air trapped
between rubber tip of plunger and
clamp.
– Air molecules are flying around & banging
into each other, sides of syringe, &
plunger tip
– Air molecules outside the syringe also
flying around; banging into each other,
outside of syringe, & back side of syringe
plunger.
– Banging produces pressure
– Air inside syringe pushes on inside of
syringe; air outside syringe pushes on
outside of syringe
11. Atmospheric Pressure
Applying force to plunger to pull it out.
– Release plunger, it slides back into barrel
by itself
– What makes the plunger go back into the
barrel where it started?
Atmospheric Pressure!
– Pull plunger = larger space but same
number of molecules
– Pressure is less inside syringe
– Pressure is greater outside syringe
– Plunger is pushed back until pressure is
equal both inside and outside
12. Atmospheric Pressure
Atmospheric pressure is pressure due
to the mass of air pulled to Earth by
gravity.
– Same in all directions - upward,
downward, & to the sides
– Air is pushing on every side of you &
everything else on Earth’s surface with
equal force
CompleteAtmospheric Pressure at
Work sheet
13. Vocabulary
Compress
– squeeze (air) molecules into a smaller
volume (space)
Pressure
– force or push caused by moving
molecules
Atmosphere
– layer of air around Earth
Atmospheric pressure
– Force applied in all directions by the air in
Earth’s atmosphere
14. Content
Whathappens when air is pushed into
a smaller space?
– Air molecules move closer together,
resulting in compressed air
What causes atmospheric pressure?
– The weight of air
Homework: Read The Pressure is On!
and answer questions
15. The Pressure is On!
What is atmospheric pressure and
what causes it?
Is atmospheric pressure higher on a
mountaintop or at sea level?
Why did the bag of chips puff up over
Tioga Pass?
Why was the empty water bottle
crushed when they returned to San
Francisco?
16. Summary: Heating Earth
What causes uneven heating of Earth’s
surface?
How does uneven heating of Earth’s
surface results in convection currents?
What is atmospheric pressure and
what causes it?
In what direction does atmospheric
pressure push?