A great way to improve the quality of your animations is to make your movements less linear and more curvy.
This is what Disney animators call the arc principle, and it's one of the 12 principles they used in the 1930s to propel their studios to global success.
In this article, you'll discover why arcs are essential and the best ways to use them in your animations for maximum effect.
Read on for practical tips!
What's the Arc Principle?
The arc principle refers to the visual path taken by objects or characters as they move through space. This path is often an arc rather than a straight line to mirror how things move in the real world.
For example, a swinging arm doesn't travel straight from one point to another but rather follows a parabolic trajectory. Note how One Piece animators play with Luffy's arm trajectory to make scenes more appealing:
Why Is the Arc Principle Important?
As previously mentioned, arcs make animated sequences more realistic. In fact, most movements follow a curve: the swing of walking legs, the path of a bouncing ball, or to convey momentum for a follow-through.
But they also make scenes more appealing: our brains are hardwired to appreciate these natural curves. When an animation lacks them, it appears stiff.
Movement paths can also act as storytelling tools to showcase the personality traits of characters or their emotional states: a character who moves in sharp, angular paths seems tense, while another who moves in smooth arcs appears more relaxed.
1. Plan with Thumbnails, Storyboards & Animatics
Good planning makes sure that the arcs remain consistent while saving time and effort: when you know the trajectory the motion should follow, you avoid unnecessary revisions.
- Align arcs with character intentions - Think about the motivations and emotions that underlie your character’s movement. Aligning the arcs with these intentions adds not just to the physical movement but also to the storytelling.
- Sketch thumbnails or storyboards to map out key poses and arcs - Before you animate anything, take the time to sketch out storyboards. These rough drawings give you a bird’s-eye view of your animation to help you lay down key poses and the arcs they’ll follow.
- Use animatics to test flow - Convert your storyboards into animatics—moving storyboards that include timing, motion, and transitions. They'll allow you to visualize how well your arcs and poses flow over time to polish them before committing to the full animation process.
2. Arc Visualization With Motion Paths And Onion Skinning
Visualizing arcs is key to understanding the natural progression of your movement. You can use two DCC tool features for this use case:
- Motion paths - Motion paths allow you to see the trajectory of a movement across a series of frames. By observing these paths, you can adjust the motion to follow smooth, circular arcs rather than linear ones.
In Blender for example, the motion paths are shown in red for past frames and green for future frames:
- Onion skinning - Onion skinning shows you multiple frames at once to see their progression over time. This way, you can make sure your arched animations will render well.
3. Easing For Realism
Without proper timing and spacing, arcs would look off. While timing is the rhythm of your animation, spacing is the distance your object travels between each frame.
Think of a car coming to a stop or a sprinter pushing off the blocks. The secret to animating these motions lies in easing, also known in animation as the slow in/out principle.
By adjusting the spacing of your keyframes, you create the illusion of acceleration and deceleration to make movements look smoother. Start by having more frames closer together at the beginnings and ends of motion.
In Blender, the graph editor is your best friend when it comes to easing. By manipulating ease curves, you can fine-tune how animation properties change over time. Smooth, S-shaped curves tend to produce more natural motion, while sharper curves can create more snappy, dynamic movements.
4. Exaggeration For Storytelling
Animation isn't just about replicating reality: you need to push boundaries for the sake of storytelling.
By amplifying your arcs, you inject energy into scenes.
- Push the boundaries - Begin by stretching the arcs of a character's movement slightly further than you initially planned. Experiment with the degree of exaggeration. For example, when a character runs, consider a more pronounced curve in their pose. Naruto's ninja run is iconic precisely because of the exaggerated arched body:
- Facial expressions - But arcs aren't confined to limbs and bodies: you can use them in facial animations as well. When transitioning from a frown to a smile, watch for the arcs formed by the eyebrows and the corners of the mouth. Emotional states also influence the arc of your lip-syncing. Look at all the arcs used in the body language of Homer Simpson, showing how he goes from discomfort to shock:
5. Don't Forget Follow-Through & Overlapping Action
A fluid arc should include other animation principles like follow-through and overlapping actions.
Follow-through action is the continuation of movement beyond the primary action. A jumping character will have her hair, loose-fitting clothes, and limbs trail behind the main jumping action. If arcs are involved, they'll also influence the follow-through. Same with overlapping actions, where different parts of a character move at different rates.
- Use reference footage - Import reference footage in your DCC tool and notice the delays in movement, like how a hand swings after the arm stops swinging.
- Break down the motion - When planning your animation, divide the actions into primary and secondary movements. Think about which parts should lead and which should follow.
- Animate in layers - Focus first on the core motion, adding follow-through elements afterwards. This method helps keep track of the sequencing and the impact each element has on the overall movement.
6. Anti-Principle: Linear Animations
Rules are great, but they are meant to be broken!
There are scenarios where deviating from arcing motion with linear movements is not just effective, but necessary to convey a specific mood or idea.
Linear motions are perfect for depicting mechanical entities like robots or machines because they come across as precise, calculated, and unnatural. In Cyberpunk Edgerunners, Adam Smasher's animated movements are just translated frames:
They can also be used to create a feeling of tension or unease. Sudden, direct movements break the fluidity of a scene and introduce abrupt moments for horror scenes or plot twists.
Inversely, an abrupt, straight-line exit of a character from a scene, ignoring all physical laws, emphasizes the absurdity or urgency of the action to create laughter.
Conclusion
The arc principle contributes significantly to the visual rhythm, realism, and appeal of movements. You don't need much to improve your animations:
- Start by sketching key poses. Visualize and draw the arc path that connects these poses.
- Use guidelines or onion-skinning techniques in your animation software to see the path of your motion.
- Arcs are not just about positioning but also timing. The speed of motion along the arc affects the animation's fluidity.
- By pushing poses and extending the path beyond what might be realistic, you can amplify the expressiveness of your animation.
- Once your character's primary action concludes, elements like clothing, hair, or limbs continue to follow the arc's path.
Make sure to have a look at the 11 other animation principles to get a better understanding of the arc principle and how they all relate to each other, but don't forget to sometimes break the rules and use linear motions for interesting results!
