Chapter 14: Gases

Atmosphere

→ The layer of gases around Earth

How is the atmosphere held on Earth?

→ Gravity pulls the air down

Where does the energy of air molecules come from?

→ The Sun heats them

We live at the bottom of an….

“ocean of air”

Air is thicker (denser)

near the ground

Air is thinner

up high (like on mountains)

Atmospheric Pressure

→ The weight of air pushing down on you

Why don’t we feel pressure?

→ Because pressure pushes on us from ALL directions equally

Why do ears pop on a plane?

→ Pressure changes as you go up or down

Why do bottles crush when going down a mountain?

→ Outside pressure increases and crushes them

Do straws “suck” liquid up?

NO, Air pressure pushes the liquid up into your mouth

Vacuum cleaners

→ Don’t “pull” dirt
→ Air pressure pushes dirt into them

Barometer

→ Tool that measures air pressure

How it works

→ Uses mercury in a tube
→ Higher mercury = higher pressure

Higher mercury =

higher pressure

If you go up a mountain

Mercury level goes DOWN

Does tube width matter?

NO → height stays the same

Why not use water?

→ Water would need a HUGE tube (too tall)

Max straw height (water)

→ About 10.3 meters

Would a straw work in space?

NO → no air pressure

Boyle’s Law

Pressure and volume are opposites

Bigger volume →

lower pressure

Smaller volume →

higher pressure

If volume becomes 3× bigger

→ Pressure becomes 1/3

Buoyant Force

Upward push from air

Yes — air pushes on YOU too!

Archimedes’ Principle

→ Works for air AND water

Why balloons float

→ They are lighter (less dense) than air

When balloon stops rising

FB = Wballoon

Wair = Wballoon or

ρair = ρballoon.

Upward force =

weight

Density of air =

density of balloon

Bernoulli’s Principle

Faster-moving fluid = lower pressure

Faster-moving fluid =

lower pressure

Fast air =

less pressure

Slow air =

more pressure

Hose
Squeeze it

→ water speeds up (narrow space, goes faster, less pressure)

Roof lifting off
Fast wind above →

low pressure → roof lifts

Airplane wings
Air moves faster on top (less pressure)

→ plane lifts (more pressure)

Convertible car top
Air moving fast →

top lifts

Umbrella flipping

→ Pressure difference flips it

Continuity Principle

Narrow space →

fluid speeds up

Continuity Principle

Wide space →

fluid slows down

Plasma

Super hot gas with charged particles

Plasma Contains

→ Ions + free electrons

Plasma How it forms

→ Very high heat or energy

Most of the universe is

plasma

plasma is

conductive