Traditionally, the standard frame rate for an animation is 24fps (frames per second). Originally animators would create a separate drawing for each frame. This would be a lot of work!
Now it is more common to use 12 frames where each frame is duplicated once. This allows animators to use only 12 images to create the full 24 frames and saves a lot of time, yet looks the same to our eyes.
When each frame displays 2 times, this is called having a "step" of 2.
The amount of visual space between one image and the next (within a set period of time) creates a sense of speed:
Changes in Speed
Gradual increases or decreases of the visual space (between consecutive drawings) leads to acceleration or deceleration:
The strength of movement and gravity both have an impact on the timing of an animation and can add to believability.
- A ball dropped from a high place will gradually accelerate due to gravity
- A ball dropped from a lower height will accellerate less
- A ball thrown with a lot of force will start out fast and slow down over time
- The same ball thrown with less force will still slow down but also will be slower overall and travel a smaller distance
- A bouncing ball gradually slows down as it reaches the apex of it's arc
- A bouncing ball speeds up as it reaches the bottom of it's arc
Anticipation is the preparation for an action. Using anticipation adds both complexity and believability to the movement.
Since this is a bouncy ball, it will squash as the ball hits a surface and stretch as the ball bounces away from that surface.
In the case of a bouncing ball, if the size of the ball keeps changing randomly, the ball loses a sense of believability. Adjustments to scale can be a good thing - if they are deliberate. If the ball (or any object) gets smaller as it moves it will look like it is moving further away. If the ball (or any object) gets larger as it moves, it looks like it is moving closer. This is especially true if the position of the ball/object changes position closer or farther away from the horizon line.There are many other aspects where consistency is important.
Characters rely on consistency. If the size or shape or position or sometimes even color of a facial feature or other body part keeps changing, the lack of consistency leads to a lack of believability.