2.14. Gases http://www.ck12.org
FIGURE 2.29
creates pressure. Pressure is defined in physics as the amount of force pushing against a given area. How much
pressure a gas exerts depends on the number of gas particles in a given space and how fast they are moving? The
more gas particles there are and the faster they are moving, the greater the pressure they create. To learn more about
gas pressure and how to measure it, go to this URL: http://www.wisc-online.com/objects/ViewObject.aspx?ID=GC
H5004.
FIGURE 2.30
The arrows show that particles of a gas
move randomly in all directions.Q:Look at box A and box B in the previous question. Is air pressure the same in both boxes? Why or why not?
A:Air pressure is greater in box B. That’s because there are more air particles in box B to bump into each other and
into the sides of the container. Therefore, the particles in box B exert more force on a given area.
Pressure in the Atmosphere
We live in a “sea” of air called the atmosphere. Can you feel the air in the atmosphere pressing against you? Not
usually, but air actually exerts a lot of pressure because there’s so much of it. The atmosphere rises high above