1. Gases and Plasmas
Gases, like liquids, flow and take shape of their containers
Both classified as fluids
Archimedes' principle, buoyancy, etc. hold for gases as well
Main difference is spacing between molecules
Molecules in a gas are very far apart => easy to compress
Plasma
Electrified (or ionized) gas
Not so common on Earth, but dominant phase of matter in universe

2. Earth's Atmosphere Blanket of air surrounding the Earth
Thins as altitude increases
Balance between heat of the sun and gravitational pull of Earth
At cooler temps – Gases condense => very thin atmosphere
At higher temps – Greater random thermal motion => molecules can exceed escape velocity of Earth => no atmosphere

3. Atmospheric Pressure We live in an “ocean” of air
Air in an avg. sized room weighs about as much as you do
Pressure inside our bodies equals that of surrounding air, so we don't notice. (Top picture)
Why does the mass in the bottom picture rise? Is it sucked up or pushed up?
Same mechanism responsible for operation of suction cups and straws
Otto von Guericke (vacuum pump)
Two teams of horses couldn't pull evacuated hemispheres apart
She doesn't notice the weight
of the water in the bag.

4. Boyle's Law
What is the source of air pressure in, for example, an inflated tire?

5. Boyle's Law
What is the source of air pressure in, for example, an inflated tire?
The constant bombardment of the tire's inner wall by air molecules in random thermal motion
Temperature is a measure of the avg. kinetic energy of a gas
How does the pressure change if (at constant temp.) you
double the number of molecules?
compress the gas to ½ its volume?

6. Boyle's Law
What is the source of air pressure in, for example, an inflated tire?
The constant bombardment of the tire's inner wall by air molecules in random thermal motion
Temperature is a measure of the avg. kinetic energy of a gas
How does the pressure change if (at constant temp.) you
double the number of molecules?
compress the gas to ½ its volume?
PiVi = PfVf

7. Buoyancy in Air
Archimedes' principle holds in gases as well as in liquids
An object surrounded by air is buoyed up by a force equal to the weight of the air displaced (~ 12 N/m3)
Why does a helium balloon rise?
What about a hot air balloon?

8. Buoyancy in Air
Archimedes' principle holds in gases as well as in liquids
An object surrounded by air is buoyed up by a force equal to the weight of the air displaced (~ 12 N/m3)
Why does a helium balloon rise?
Helium is a lighter gas than oxygen, nitrogen, etc.
What about a hot air balloon?
Heated air yields same pressure with fewer molecules => less dense than surrounding air

9. Fluid Dynamics
Since water doesn't “bunch up”, the same amount of water flows past any given section of pipe in the same amount of time
What does this imply about the flow of water through pipes of varying diameter?

10. Fluid Dynamics
Since water doesn't “bunch up”, the same amount of water flows past any given section of pipe in the same amount of time
Water flows faster as pipe narrows
Putting your thumb over a garden hose
Bernoulli's Principle
When the speed of a fluid increases, internal pressure in the fluid decreases.
Conservation of Energy
Kinetic energy increases as work associated with pressure forces decreases and vice-versa.
More closely spaced
streamlines represent
faster flow.

11. Bernoulli's Principle
What happens to your shower curtain when you turn the shower on?
How does Bernoulli's principle explain
a curveball?
the lift of an airplane wing?

12. Bernoulli's Principle
What happens to your shower curtain when you turn the shower on?
How does Bernoulli's principle explain
a curveball?
the lift of an airplane wing?
Demo – blowing across the top of a sheet of paper

13. Plasmas Gas of ionized atoms Plasma is electrically neutral
Ion: An atom that is stripped of one or more of its electrons
Electrons are charge carriers: responsible for electric current in household appliances
Plasma is electrically neutral
Same number of postive ions and electrons, but
Highly electrically conductive
Can be shaped, molded, and moved by magnetic fields
Fluorescent lamps, lightning, newer TVs all involve plasmas
The sun (and all stars) are balls of hot plasma
Most common phase of matter in the universe