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>> Shattering and splashing. So instead of bouncing whole, when you have an object hitting
the ground, the impact may cause a solid object, like a brick, to shatter or you may have a
splash. So if the water balloon happens to burst then it will splash instead of bounce.
In this case we have separate pieces, fragments of the brick or water droplets which are thrown
into the air. Here's some nice drawings from Dillon's Elemental Magic. Very, very nice
book if you don't have it, definitely recommend it. So let's look at an example here of a
brick drop where the brick shatters. So this is in slow motion so you can see the details.
So you see these two fragments happen to break off. Now in this example it reminds us that
regardless of the size of a fragment or the speed of the fragment, each fragment will
be a certain time in the air that depends only on how high that fragments goes. So in
that example we just saw there were two pieces that broke off simultaneously. The small piece
happened to go fast but low to the ground so it hits the ground first. The other piece
flies up higher and then it hits the ground next. If you don't have this kind of timing
correct then the different pieces look as if they're moving in different gravity. Now
splashing is, as I said, similar in many ways to shattering. So if we have a liquid that
is striking the ground then we have different parts, which splash up. We even have a splashing
with granular materials like sand or flour. In this case we don't form individual droplets,
just the separate grains of splash on impact with the ground. So in a sack drop, of course
if the sack bursts, bursts, then we see this kind of splashing, but even when it doesn't
burst, just the grains moving and splashing inside the sack, give us noticeable popup
of the sack on impact. Now when we have pieces flying off from an object that shatters or
droplets from a splash, we want to avoid having unrealistically synchronized motion. So to
make these look believable it requires a certain randomness in the sizes, the speeds, the directions,
so forth. So often the smallest pieces tend to fly off faster but that's not a hard and
fast rule, so we want to have a natural randomness in a splash or a shatter. Now when we don't
have that randomness then it's very distracting and in animation this is called twinning.
So one of the reasons that patterns are distracting for us is that we have very, our brain has
very good pattern recognition and so even when something is fairly camouflaged our brains
are wired to detect patterns and that tends to be distracting in animation, unless you
specifically want to have that pattern. So the same thing, since we're talking about
twinning, the same thing happens in character animation if the character's motions, say
what the character's doing with their arms as they're talking, if that motion is too
symmetric then it's distracting and sort of resembled cheerleading. So this is what's,
as I said, called twinning in animation. Now getting back to splashing and shattering,
suppose we have a bucket of water and we take that bucket and we drop it from a certain
height. Now we ask the question, is it possible for some of the splash to actually rise higher
than the height from which we drop the bucket? Okay, so could some of the droplets actually
reach a greater height than where we drop the bucket, and the answer, turns out, as
yes. The same thing with fragments from a shattered object; some of them can reach a
greater height than from where the object was dropped. Let's look at a quick video of
that. [Background sounds] So if you look carefully you see that in this splash there are several
droplets here that are going over my head, much higher than where I released the can
full of water, and in fact if you look very carefully you see that some actually go quite
high; they're circled here in red. Now to understand how this is possible, consider
this demonstration where I'm dropping a ping pong ball that is above a golf ball. So I
drop them together, so here you see the two of them and I drop them, [ball dropping] you
see clearly the ping pong ball is rising much higher than the original height that it's
being dropped from. So one more time. [Ball bouncing] So what's going on here is the two
of them fall together and the golf ball happens to hit first because it's on the bottom and
it strikes the ground, it's now rising upward. The ping pong ball is coming downward, of
course this happens very quickly, so now the upward motion of the golf ball, which is much
heavier than the ping pong ball, it's almost like a baseball bat being swung and striking
a baseball. So in this case the speed of the ping pong ball is much higher than it would
be if the ping pong ball simply hit the ground by itself. And if these are all perfectly
elastic then the speed of the ping pong ball could actually be magnified three times larger,
which leads to the height, again if everything is perfectly elastic, the height could be
up to nine time higher. Here's a very similar demonstration but even more exaggerated. [Balls
dropping] We have a stack of elastic balls and [ball dropping] the little red one sits
on that stack and so it's the same, [ball dropping] same thing we saw with the golf
ball, ping pong ball, but it's a ball hits ball, hits ball and then finally the red one
flies off extremely fast. You can find this toy in toy stores. It's a lot of fun. So in
summary instead of bouncing a solid object may shatter into fragments and something which
is liquid, like a water balloon, may splash into droplets. The time in the air for the
fragments or the droplets only depends on how high they go. Shattering and splashing
should be irregular otherwise it's going to look unnatural and that's referred to, in
animation, as twinning; when two things seemed to be synchronized in an unnatural fashion
as they move. And the height reached by some of the fragments, or some of the droplets,
may exceed the original height from which the object fell. So that actually makes it
look even more natural to have splash like that. Of course, whenever you're doing these
types of animations shoot as much reference as you can because sometimes things are surprising
in nature.