One of the biggest challenges in animation is
how to create the correct feeling of weight. How do you make it so a heavy object or character
really feels heavy and strong and forceful? And how do you make something light
feel very delicate and elegant? In this video we're going to talk about the most important aspects of physics that
every animator absolutely has to know. If you are able to animate weight
correctly, you have an animation superpower! Your audience - they know
how big and he
avy characters move. They know how small and light animals
move, because they have seen it in real life. You need to meet their expectations. If you
want to tell your audience that something is light you need to move it a certain
way, so that they can believe that. It's pretty cool that we only have
to look at reality a little closer to learn what we need to do in our animations. As a first example, I want to show
you what happens when I do this finger flick on a piece of paper: The force f
rom the finger flick is
enough to make it fly across the table. In contrast we have a big heavy book here
and if I flick it with my finger - nothing is happening. I'm not putting enough
force onto this book to make it move So let's put that in some general
rules that we can work with: Heavy objects are more resistant.
They need more force to start moving. Light objects are less resistant. With only a little bit of force they can
already start moving a lot. So here's a very simplified examp
le of a light
object being shoved by this ball. And you see how you know the glass has no no resistance.
It just immediately starts moving with it. In contrast if you push something heavy
you can see that there is this resistance. Our ball has to really push and then it
starts moving really slowly and speeds up. So you see a big difference of how you have
to treat moving lighter and moving heavier objects and characters. This is not only true for starting a motion. It's
also the case for c
hanging direction or stopping. Let's take for example a heavy drone robot: If it wants to change direction, it has to apply a lot of force to catch its weight
and move it back into the other direction. In contrast, here, we have a light bird. And the bird can just zip around in fast speed,
start, stop and change direction just like that. It's a completely different rhythm of motion. And we can take this a little
further. What I did here... After just one or two frames this
light ball is up t
o full speed again. It can just lightly bounce around
and it doesn't have a long period of speeding up and slowing down. In comparison, I have this animation here of what I was imagining could be more
like a a monkey swinging in the tree. It needs to use anticipations and overshoots, because it's swinging back
and forth in much more frames. It needs to build up a momentum.
It needs to build up a force to push its mass to the next position.
And that makes it a lot slower. It's important to n
ote though that heavy
characters and heavy objects - they take a lot more effort and force to speed up, but
they can be sped up to be really, really fast. But what happens if we stop objects of different
mass or of different weight all of a sudden? Well I have no problem catching the
paper my hand doesn't even move. I can just, you know, catch it out of the air. But catching the book is a lot more difficult. I
have to really work against the mass of the book. I have to go along with it to t
ake the
momentum out of it. So as you can see i need to apply a bigger counter
force to make the book stop. The general rule is that
objects would like to stay in the state that they're in unless
an unbalanced force is applied. And that's very easy to understand for objects at
rest. We just instinctively know that, you know, the book resting on the table, it's gonna
stay that way unless I apply a force to it. Objects in motion would
also like to stay in motion. If we imagine that we are a
n astronaut
and we are throwing a ball - the ball is gonna continue flying in that
direction until it hits something. On earth, a ball just rolling on
the ground is gonna stop eventually, because there's the friction of the ground applying a counter-force taking momentum
out of it until it comes to a full stop. So if things would like to continue moving
in the direction that they started moving, what does actually happen during an impact? The first thing that I want to
point your attention
to is that heavy and light objects fall at
approximately the same speed. They reach the ground at the same time! There's an exception for it if
there's air resistant involved. If I would let a piece of paper fall,
obviously, it will fall slower. But generally, heavy and light things fall at the same
speed, they reach the ground at the same time. That might feel a little bit weird to you
now, because we learned that objects with more mass require more force and often that
means more time t
o speed them up, right? The reason is that the force of
gravity on heavy objects is bigger than on lighter objects. And that kind of
compensates for heavy objects being slow to start. So often times, when we see things fall, we
don't actually get information about the weight but about the scale and the
distance that they're falling. This is the formula for calculating a free fall. We can solve it either towards the
distance d or the time in seconds t. This way we can find out that a fall fr
om
1.2 meters or 3.9 feet takes half a second. A fall from 20 meters or
65 feet takes two seconds. But there's a one moment that
gives us all the information about the weight and the material of
an element and that is the impact. Let's have a close look at what
happens with this tennis ball and this book when they impact on the table. On the moment of impact, they released the
kinetic energy they gained during their fall. The speed is the same for both of them, but
because of its larger m
ass and larger force, the book gained more energy. Energy cannot disappear. It always comes
from somewhere and goes to somewhere. Let's assume our ball is made from a fictional,
impossibly light and extremely elastic material. Instead of giving off energy to the table, it would just take all of it onto itself
and jump up to exactly the same height. It's plus and minus the same amount of energy. But many objects resist to
changing their direction like that, because of their mass and a non-ela
stic material. They turn a good portion of the energy
from the fall into something else. The energy of the book creates mostly deformation
and destruction on both, the book and the table. If we would let the book fall multiple times,
after a while, we would see some wear and tear. There's also some motion sideways and you
can see the cover page being lifted up. And then of course there's also sound. The book makes a loud bang and the
tennis ball is not really audible. The tennis ball is som
ewhere
between these extremes. Some energy was lost on the table, some
went back into the ball to make it jump. This doesn't mean that all light materials bounce. This piece of paper got sent rolling
sideways because of its uneven surface. And many light materials like cloth and paper, they lose most of their very little
energy because of deformation. So this was the impact with something that
that can't move, that cannot make way. But here we have two tennis
balls that both can move. And
when the first tennis ball is rolling into
the other one, it splits up the kinetic energy. It keeps a little bit of it and continues rolling, but it also gave a lot of it to the second
tennis ball, which is now rolling as well. But of course, we also have the friction
of the table, which takes out the momentum until the balls come to a full stop. So, applied to character
animation all of this means that light characters are quicker to speed
up, slow down and change direction. They are tosse
d around very
easily by bigger masses. If we have a heavy character that character
is probably slower to speed up, slow down, and change direction. A bigger character is not easily tossed around. Now, especially if you're
only starting with animation, it's extremely important that you practice this. So, my suggestion would be if you've
never done anything like this before: Do these exercise animations that
I showed you, these examples. Animate them yourself and
observe how the resistance w
orks and how the forces go from one object
into another object. Really practice that! If you want, we can do some of them together,
because I have a premium bonus lesson for you, where I walk you through the creation of some
of these exercise animations step by step. And we're even going to create this fun character animation with two characters
of different weight in Open Toonz. In the free track of this 2d animation course,
we're gonna have a look at keyframe animation, which is almost ma
gical, because the
computer is doing some of the work generating in-betweens that you don't have to draw. However, if you want to support me, I'd be
very happy and feel honored if you consider getting the premium tutorial. It will not only help me, make more free
and paid classes for you to learn animation, but the premium tutorial will also help you to build the skills you need to create
animations that make the right impact. In any case, I hope to see you again in
one of my classes. I hop
e you enjoyed it and thank you very much for watching! Keep on animating!
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