1. . P Hydrostatics-An Introduction Liquid
We can break the word "hydrostatics" into its components to get some idea of the subject. Hydro- relates to water as in hydroelectric power. Much of fluid mechanics was developed with water in mind, but the principles apply to other fluids as well. The word "statics" refers to a subset of the area of physics called mechanics, where motion is absent.
An important concept in hydrostatics is pressure. What is pressure? It is often defined as the force per area(F/A). This is not quite correct since pressure is a scalar quantity and we know that force is vector. The force associated with pressure acts perpendicular to a surface. It is called a "normal force." As such, the direction is implicit when we say pressure is force per area.
Patm 
Liquid P .
Inside a fluid, the pressure acts the same in all directions. That is,
it is isotropic.

2. Liquid
Pressure increases as we go deeper in a fluid. If you’ve ever
been swimming, you probably noticed the effect of the greater
pressure on your ear drums as you propel yourself underwater
to the bottom of the pool.
This increased pressure makes sense because you have the
weight of the liquid above acting on your body.
Within a continuous body of liquid, the pressure is the same in a horizontal plane(same depth). In this case, the force associate with pressure is easily found by multiply pressure times area(P A).
An enclosed fluid can transmit a force. F1 F2
P = F1/A1 = F2/A2 A1 A2
The braking system of a car is a practica
example.

3. Look closely at the two illustrations in the previous slide
Look closely at the two illustrations in the previous slide. Because liquids are incompressible, a
force or pressure exerted on a fluid is transmitted through that fluid. This is true for the braking
system and for the swimming pool. Atmospheric pressure Po acts on the surface of the water in the
pool. Po is transmitted through the water to give an added force on the wall. This component of
pressure is constant and does not change with depth. The total pressure on the wall is given by
P = Po + γy
where γ is the specific weight of the fluid and y is the depth.
Understanding and being able to determine the forces
due to hydrostatic pressure can help us with the design
of large storage for oil or other liquids.
It is important to master the physics and mathematics we will encounter in studying hydrostatic
forces and torques! These will help you be successful in this course.