Brendan's Bouncing Ball Lecture

Exploration, Analysis and Application of the Bouncing Ball

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The bouncing ball is crucial in animation because it can be used to give weight and life to a character. It is essentially just a trick or formula, but once learnt it can then be applied to a million different things.

I'll be showing in detail how and why it works and what happens when it goes wrong. I’ll then go on to show how it can be applied in animation.

Bouncing Ball

This is almost a textbook perfect bouncing ball. Ideally, the squash shapes wouldn’t be perfect ellipses - there should be more of the ball’s underside in contact with the ground. This would help with the strobing during these frames to. Unfortunately I did this in the program Maya, with limited time and perfect ellipses are what Maya likes to make. But hopefully these animations are good enough to demonstrate what I’m talking about.

You'll notice that this animation is not strictly realistic, it is an exaggeration of what a real ball does. And this is essentially what animation is - a caricature of life. If I wanted to animate a realistic bouncing ball I would still use the following formula, but I wouldn't use this level of exaggeration.

The basics of the bouncing ball are spacing and squash and stretch. We’ll explore what happens when you vary both of these. First, we’ll look at spacing.

Bouncing Ball with Guide

Here's the same animation with a guide following the top of the ball so you can see the spacing more clearly.

If you follow this movie from the start you’ll see that the spacing increases as the ball accelerates under gravity toward the ground. There is then a big gap in the spacing. This gap is a crucial part of the bouncing ball, it gives the animation it's punch and weight. You really want to push this gap as much as possible. The bigger this gap is, the lighter the object, the smaller the gap, the heavier the object. But, even in heavy objects, this gap should be considerable.

After this gap there is the most extreme squash frame followed by another frame that is in contact with the ground. The top of the ball in this drawing is near to, or 'favouring', the previous squash drawing. Having two frames at the bottom is also essential. After this, there is then another gap up, then the spacing decreases until the ball is back to it's original position.

The stretch on the ball is only used when the ball is moving fast. If the stretch is applied when the ball was moving slowly (near the apex) it would destroy the illusion of a solid object and we would get the effect of something far more flexible, such as a water balloon.

Bouncing Ball on ‘2’s

This lecture is designed not to be specific to one type of animation - drawn or 3d computer animation. However there are certain considerations in both. In traditional, drawn animation it would be likely you would first animate the ball on '2's. As we can see, the animation still works on ‘2’s, the problem we have though, is of increased strobing. However, it would be a mistake to create inbetweens over the whole animation so it was on ‘1’s. This could make the whole thing look like it's under-water. And it’s really not necessary over the whole animation as the top part still looks smooth. I would reccomend only inbetweening the lower part of the animation. But keep in mind your spacing. For example, don't put a straight inbetween in the gap before the squash, this would take the punch out of the motion. Much better to keep the gap in mind when you inbetween this, and push the drawing up, favouring the previous frame. A combination of ‘1’s and ‘2’s gives texture to the animation.

Bouncing Ball, Line Test vs Solid


Here we have the bouncing ball on ‘2’s again. And although, this doesn’t show it very clearly, the rule is - animation strobes more in solid form than it does in line test. This is because the solid ball has more contrast and therefore the individual frames are more apparent. So, if your animation is on ‘2’s and parts of it are strobing in line test, then you should inbetween those parts as they will DEFINITELY strobe when they are coloured.

Bouncing Ball, No Squash


Back to looking at spacing, as you can see from this animation, the spacing is so important that we can take the squash out of the animation and the ball still has weight. However, without squash the ball loses life, it looks dead, like a ball bearing. But it definitely has weight. So we can deduce that the squash and stretch adds life and spacing adds weight.

Bouncing Ball, Even Spacing


In this movie I have evened the spacing out, in each drawing the top of the ball is equidistant from the drawings either side of it. As we can see this effects the animation greatly, it suddenly looks very inorganic and machine-like. The animation is helped a little by the squash in it, but it is easy to imagine how completely robotic it would look if we took this out.

It’s very easy to make animation that looks like this - manmade and inorganic, and even spacing is often the culprit. The other offender is even timing, now that the ball spends the same amount of time at the bottom as it does at the top we have a very dull and monotonous motion. The ball looks much better when it spends longer at the top and just 2 frames at the bottom. So, in your animation, always strive to vary your timing and make sure your spacing isn’t even.

Bouncing Ball, 4 Frames of Squash


Now let’s consider weight in animation and how to vary it. A mistake often made is thinking that more frames of squash will add more weight to an object. As you can see, this is not the effect that it creates, it is even more apparent in the next animation ...

Bouncing Ball, 6 Frames of Squash


... in which I have 6 frames of squash at the bottom. The affect achieved is not of more weight but instead the ball starts to look like a small jumping creature such as a frog. It is worth noting that this can be an effect you want to achieve, if you were animating a frog. As with all examples I’m showing, there are always exceptions. The trick is to understand the formula so you can break it if and when you need to.

Bouncing Ball, 1 Frame of Squash


As you can see having only one frame of squash is also a mistake. The illusion of weight has been lost as our squash frame just flashes at the bottom of our animation. This is a common mistake, especially when trying to steal some frames to speed up an action, but reducing the time spent at an extreme to only one frame rarely works well.

3 Bouncing Balls, Different Gaps


We’ve seen that varying the number of frames of squash in our ball animation is an unsuccessful way of altering the weight of our ball. The way to achieve this is in the spacing. As you can see, these balls appear to have different weights; the one on the left feels like a ping pong ball, the one in the middle, a tennis ball, and the one on the right feels more like a bowling ball (if it wasn’t squashing as much ... and bouncing).

3 Bouncing Balls, Different Gaps, with Guide


This is the same animation as before, with a guide added, and you can now see all I have done to alter the weight is vary the gap between the last stretch and the squash. The top part of the ball animation is the same in all three, as is the timing. Note that the gap in the heavier ball is still considerable.

3 Bouncing Balls, Different Gaps, Different Sizes


If we were to now apply character design, or in this case scale, to the animation we can see how well the illusion of weight works. We can now start to see these as different weighted characters. If they were cartoon woodland creatures, the one on the left could be a squirrel, the one in the middle, a fox, and the one on the right, a bear.



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© Brendan Body 2008