layers due to cooling. The cooling tends to
increase the density of the air.
Atmospheric pressures are quite large, but in
most instances practically the same pressure is
present on all sides of objects so that no single
surface is subjected to a great load.
Atmospheric pressure acting on the surface of
a liquid (fig. 2-3, view A) is transmitted equally
throughout the liquid to the walls of the container,
but is balanced by the same atmospheric pressure
acting on the outer walls of the container. In view
B of figure 2-3, atmospheric pressure acting on
the surface of one piston is balanced by the same
pressure acting on the surface of the other piston.
The different areas of the two surfaces make no
difference, since for a unit of area, pressures are
TRANSMISSION OF FORCES
When the end of a solid bar is struck, the main
force of the blow is carried straight through the
bar to the other end (fig. 2-4, view A). This
happens because the bar is rigid. The direction
of the blow almost entirely determines the
direction of the transmitted force. The more rigid
Figure 2-4.Transmission of force: (A) solid; (B) fluid.
the bar, the less force is lost inside the bar or
transmitted outward at right angles to the
direction of the blow.
When a force is applied to the end of a column
of confined liquid (fig. 2-4, view B), it is
transmitted straight through to the other end and
also equally and undiminished in every direction
throughout the columnforward, backward, and
sidewaysso that the containing vessel is literally
filled with pressure.
An example of this distribution of force is
illustrated in figure 2-5. The flat hose takes on
Figure 2-3.Effects of atmospheric pressure.
Figure 2-5.Distribution of force.