Day 4

1
Day 4
If you could see the particles that make up air,
what would you see?
The particles are always moving very fast. They
bounce randomly and spread out in all directions,
so there is a lot of space between particles.
2
Air Takes up Space
Investigation 2, Part 1a Where's the Air?
3
Focus on Air
Where does weather happen?
In the air that surrounds Earth.

• Air plays a very important role in the weather.
• In the next few days we are going to look more
  closely at air to learn some of its properties.

4
Syringe Activity

• Fill the syringe with water.
• Seal the end and push on the plunger.
• Repeat the activity, but this time fill the
  syringe with air.
• What can you conclude from this activity?

5
Air Investigations

• Use your syringe to investigate air and find out
  what it can do.
• Turn to Air Investigations (page 3 in the lab
  notebook).
• In part 1, record three observations and three
  questions about air.

6
Discuss Observations
What happens when you clamp the tube closed and
push on the plunger?
The air is pushed into a smaller space.
Is there more air, less air, or the same amount
of air in the syringe when the air is pushed into
a smaller space?
same amount
7
Discuss Observations
What happens when you let go of the plunger after
pushing it in?
The air pushes the plunger back out.
What do you think happens to the air when it is
pushed into a smaller space?
(answers will vary)
What do you think happens to push the plunger
back out when you let it go?
(answers will vary)
8
Air Molecules

• Draw a model to show what you think happens to
  the air molecules inside the syringe when you
  seal the end and push on the plunger.
• Draw another model to show what happens to the
  molecules when you release the plunger.

9
Gas in a Syringe

• View the animation called Gas in a Syringe.

10
Air is Compressible

• When you push on the plunger and force the air
  into a smaller space, we say the air is
  compressed.
• Air is compressible because it's a gas, and gases
  contain a lot of empty space.
• Compressed air pushes back with a force equal to
  the force compressing it.

11
Bumping Molecules
How does compressed air push back?
When molecules are pushed into a smaller space,
they bump into the inside of the syringe more
often. All of this bumping creates pressure.
12
Air Pressure

• Pressure is a force or set of forces that is
  spread out over a surface.
• Each time an air molecule bumps the plunger, it
  exerts a force called a push.
• The combination of all those pushes on the inside
  of the syringe creates the inside air pressure.
• Similarly, the molecules bumping the outer
  surface create the outside air pressure.

13
Air Pressure

• When the outside air pressure is greater than the
  inside air pressure, the plunger will move in.
• When the inside air pressure is greater, the
  plunger will move out.
• When the two pressures are equal, the plunger
  will stay where it is.