Fri., Sep. 10 In class Optional
Assignment
Question Answers
Gravity will cause a hot air
balloon to sink.
An upward pointing pressure difference force (pressure at the bottom of
the balloon that is pushing upward is stronger than pressure at the top
of the balloon pushing downward) is what causes a hot-air balloon to
rise.
These two forces are always present and it is just a question of which
one becomes dominant. If the air in the balloon is warmed, its
density will decrease and the balloon will become lighter. The
gravity force weakens and the upward pressure difference force will
cause the balloon to float upward. If the air in the balloon
cools, it will become denser and the gravity force (weight of the
balloon) will increase. The balloon will sink.
Air at the bottom of the atmosphere is compressed by the weight of all
the air above and has the highest density. Density decreases with
increasing altitude because there is less and less compression by the
weight of the air overhead.
Temperature sometimes decreases with increasing altitude (troposphere),
and sometimes increases with altitude (between 20 and 50 km in the
stratosphere). There are regions where temperature remains about
constant with altitude (between 10 and 20 km at the bottom of the
stratosphere). This is something we will be looking at in more
detail.
Pressure is decreasing with
increasing altitude, that is OK. As drawn the air
between 1000 and 900 mb would have lower density than the air betweenb
800 and 700 mb. That isn't correct. The thinnest (most
compressed) layer should be at the bottom of the picture not at the top.
