Questions
on Quiz #1 will come
from topics on this study guide together with material on the Practice
Quiz Study Guide.
Mass, weight,
density, and
pressure. Mass is the amount of a
particular substance. On the earth gravity pulls downward on a mass
producing weight. Pressure at any level in the atmosphere is a
measure of the weight of the air above (this is one way of thinking
about and understanding pressure). Pressure is defined as force
divided by area and acts like a force (a force that pushes upward,
downward, and sideways). Common pressure units and typical sea level
pressure values. What instrument is used to measure air pressure?
About when was it invented? Pressure and air density (density = mass
divided by volume) both decrease with increasing altitude (you should
be able to explain why). What relationship is there between the rate
of pressure decrease and air density (i.e. does pressure decrease
most rapidly in high or low density air)?
Sample questions (from the Fall 2000 quiz packet)
Practice Quiz: 15, EC2, EC3
Quiz
#1: 3, 17
Final Exam:
6, 11
Ideal Gas Law.
This is
a
microscopic-scale explanation of air pressure. Two equations:
P = N k T / V and P = (rho) R
T
N is the number of air molecules in
a
volume V, T is temperature and rho
is density. R and k are both constants (you can pretty much
ignore them). You
should be able to determine what will happen to the
pressure in a rigid container or something flexible like a balloon if
you change
the variables in the
equation above. What variables could you change together in such
a way
that the pressure
would stay constant?
Ideal gas law
applications. If you heat or cool a parcel of air in the
atmosphere, Charles' law says the density
(volume)
will change in a way that keeps the air pressure inside the parcel
constant (the pressure inside the parcel remains the same as the
pressure of the air
surrounding the parcel).
Upward and
downward forces acting on air parcels (the
strength of one of the forces depends on the air inside the parcel, the
other on the air outside the parcel). These two forces are usually in
balance. What happens to the balance when you warm or cool a parcel of
air? Basically you should be able to explain why a balloon of hot
low density air rises and a balloon of cold high density air
sinks.
Archimedes Law. An
object immersed in a fluid (a liquid like water or a gas like air)
experiences an upward bouyant force that is equal to the weight of the
fluid displaced by the object. Basically objects that are less
dense that the fluid around them float, objects that are denser than
the fluid surrounding them sink. What causes the upward bouyant
force?