Mechanics 2: Linear and Rotational Dynamics - 3D Math Primer for Graphics and Game Development - page 566

quickly. In many games, the character will hover at that maximum height
for a duration, and then slam back down on the ground as quickly as it rose
up, perhaps leaving a crater behind. This is clearly not physically accurate,
but then again, neither is being able to jump two or three times your own
height, steer in midair, or double jump. When it comes to jumping in video
games, reality is not just overrated, it's completely ignored. It just doesn't
feel right.
If simulating a jump mechanic using gravity makes for a bad jump
mechanic, simulating a jump mechanic using a value of 9.8 m/s 2 is even
worse. The basic problem is that most players expect a jump to take
a certain amount of time but also expect to be capable of jumping to
unrealistic heights. When real-world gravity is used to attain these heights,
the player is in the air too long, and it feels “floaty.” Many arcade racing
games also increase gravity to get the car back on the ground more quickly.
Whether it be racing games or character games, the player wants to be in
full control again as quickly as possible, and waiting for real-world gravity
to get them back down usually takes too long. And then there are other
racing games that use a value of gravity that is less than the real world
value, to facilitate unrealistic jumps at realistic vehicle speeds.
There are also reasons to fiddle with gravity for non-player-character
objects as well. Sometimes real-world gravity can create an “objects made
of styrofoam” feeling for simulated objects in general, 9 so gravity is in-
creased to get an object to tip over and come to rest more quickly. In
other situations, an artificially low value of gravity can make a large object
seem even more massive (especially when accompanied by the right sound
effects), because acceleration on Earth is constant and is one of a few cues
humans instinctively use to establish an absolute scale for objects in the
distance. 10
Hopefully, while reading the preceding design discussion you absorbed a
general message rather than focusing on our specific opinions. What “feels
right” is a subjective matter; furthermore—and this is the key point—it is
based more on player expectation than physical reality. In the end, what
matters most in a video game is not what's going on in the CPU or even on
the screen, but what is going on in the player's mind. And the human mind
is highly susceptible to suggestion. When creating video games, always
remember that the quest for realism should never be an end unto itself,
but rather a successful video game will harness realism only where it serves
the ultimate goal, which is entertainment. In fact, realism is quite often
opposed to this goal. Video game makers (especially programmers!) often
9 This is often caused by excessive damping in the physics system used to help mask
instability.
10 Fletch: I like to call this technique “Lord of the Rings gravity.” It reminds me of
the giant staircases that get destroyed during the escape from the Mines of Moria.