Differences in Timing Concerning the Weight of a Bouncing Ball

Factors that effect how a ball bounces are temperature, internal air pressure, air resistance, the surface that it contacts, rigidity, speed and weight. When attempting to simulate a bouncing ball through animation, one should consider these factors. The following focuses on how the weight of a ball effects its timing during it’s bounce. What other applications can be used from this exercise when doing more complex animation will also be discussed.

The weight of a ball will determine how high and how many times a ball bounces. To set the places in time, where and when the ball will bounce, one must position it accordingly and set keys in the timeline. First one should move the ball to the position where it's falling from and press the 'k' button to set the first key on the timeline. Next, one should move forward in time by moving the bar in the timeline and then move the ball halfway towards where it will contact the ground. The next key should where and when it makes contact with the ground.

Each bounce that follows will be less and less. The first bounce will be animated by keying the ball in the time where it should be at its highest. The end of it should be keyed where it contacts the floor. The following bounces should be created the same way except smaller than it's previous bounce. This is because each bounce that follows will be less and less. Where and when the ball has finished bouncing a key should be set at the end of it's bounce and a key to where and when it will stop. A ball would not stop dead so to make it more convincing and believable a key should be set slightly backwards, forwards again, and back to emulate the ball setting. This settling should be a movement through a minute space and should take a long time therefore the keys should be far apart on the time line.

Now one has a basic bounce but it won't be convincing. This is because a ball would accelerate as it falls and decelerate as it rises. This is called 'slow in' and 'slow out' in animation. One can control these aspects of the animation by opening the 'Animation Editor' by pressing '0'. This shows a graph with 'tangents' that are the curved lines and 'Bezier handles' which are the handles that allow one to control the bends of these lines. Currently the ball appears to move in a wave instead of having sharp bounces. To resolve this one can break the tangents by selecting the keys on the 'y' tangent where the ball makes contact with the ground and selecting the 'Mirror Slope Orientation’ button. Now the handles are broken into independent and symmetrical lines that allow one to sharpen the balls bounce from the tangents. The ball may not proceed at an even speed. To resolve this one should delete the unnecessary keys on the 'z' or 'x' tangent so that only the first and the last key are left. The Z tangent will move in one smooth motion because there will only be one curve that controls it.

The last problem is that the ball does not squash from the force when it makes contact with the ground. To simulate this in the animation a key should first be set just before and just after each bounce. This is so that the ball would only start to squash when it hits the ground instead of changing shape too early or too late. To simulate the actual squash, the pivot point of the object should be moved to the surface that its making contact with by selecting the object and holding the alt key and then scaling the ball horizontally. This will make the ball squash towards the surface instead of away from it. After scaling it, a key should be set and the same should be done at every bounce but it should be scaled less than the previous bounces.

There are other kinds of movements in animation that relate to the movement of a bouncing ball. The walking motion of a character is similar to this. A foot also moves to and from a surface much like the bounce of a ball. This is because it would make contact with the floor and separate sharply just like the bounce of the ball. The general movements of animated objects move through time and space and also include slow in and slow out movements that can be controlled with the animation editor.

References:
http://www.iop.org/EJ/article/0031-9120/33/3/018/pe8308.pdf?request-id=AICepCjl3BGk1_wf3Ai7Kg