Game Development Reference
In-Depth Information
Under Pressure
As discussed in Chapter 3 , pressure is a force applied over an area. Imagine a concrete
block sitting on a steel plate. The weight of the block will be evenly distributed over the
area of contact, creating a pressure on the steel plate. Gas and liquid can apply pressure
as well. The weight of the air pressing down on us is what is known as atmospheric
pressure.
Let's cover a quick example of how to calculate pressure just to illustrate the concepts
involved. Pressure has many different units, but all of them can be equated to a force
divided by an area. For this chapter we'll stick with Newtons per square meter, as this
is easiest to visualize. The SI derived unit (a unit of measure made up of other funda‐
mental units) is called a Pascal, which is just 1 N/m 2 .
Example Effects of High Pressure
In Chapter 3 , we discussed the concept of buoyancy and how it arises from hydrostatic
pressure. Here, we'll show the tremendous forces that hydrostatic pressure can cause
on a submerged object. Let's imagine we have a steel ball filled with normal atmospheric
pressure at sea level, or about 101,000 N/m 2 . While this seems like a lot, your body is
used to dealing with this pressure, so you don't even notice it on a daily basis! Now we
are going to take this ball and drop it into the Marianas trench, the deepest known part
of the ocean. The water depth here is approximately 10,900 meters. The formula for
calculating the pressure due to water (hydrostatic pressure) is:
P(h) = ρ × g × h
where ρ is the mass density of water, g is force due to gravity, and h is the height of the
water column above the object.
Here we take the standard density for saltwater, 1025 kg/m 3 , and calculate what the
pressure is:
P(10,900) = (1025 kg/m 3 ) × (9.8 m/s 2 ) × (10,900 m) =
109,490,500 N/m 2
Figure 23-1 shows how the pressures act against our steel ball.