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.