Investigation 4-3

1. Heating Earth
The Pressure is On!
4-3

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?