Computer-generated imagery (CGI) is in more movies than you might think. Whether it’s enhancing a background, adding fog to breath, or even drawing Iron Man’s suit when he’s just standing around, it’s often invisible. If it’s done right, we barely even notice it.
But if it’s done wrong, it stands out. There are a lot of ways CGI can go wrong, but we’re going to focus on one thing: physics fails. In a physics fail, the CGI object is either way too light or way too heavy. When it interacts with real objects, the CGI does not have the right amount of weight or momentum. When a physics fail happens, it makes the audience painfully aware of how fake a movie is.
For example, nothing about this tank turret throw from Fantastic Four makes any sense whatsoever. How could a 500 lb rock monster anchor down several tons of steel? Why does the steel shatter? How come the impact doesn’t cause the nearby sand to scatter? Why does the blast fire out equally in all directions?
Sure, the Thing doesn’t exist, but for the space of 2 hours the movie is asking us to believe he could exist in a world like our own. Every time the CGI breaks the laws of physics, we get slapped in the face by reality.
Fantastic Four had comically bad CGI, but it’s far from the only movie with physics fails. Sometimes a physics fail happens for the sake of the plot, like with this incredibly lightweight helicopter because the effects team just didn’t bother to calculate for weight limitations.
Sometimes a physics fail is just the result when a fake object and a real object interact, like when the director forgets that a desk should wobble or tip when an elf jumps onto it.
So, how can directors make CGI better?
Well first, if they fail at physics, learn better physics.
Secondly, remember your audience is smarter than you think they are. Even a 12 year old can tell the difference between which scenes were shot on location and which action sequences were shot on a soundstage in Hollywood.
And lastly, keep it real. Be more creative and find ways to make the effects using real life elements, robotics, animatronics, puppets and other creative arts that brought Hollywood magic to life in the first place.