There are a number of principles when it comes to animation and the way that things move in order for them to appear natural, here is a just a quick revision of these principles in my own words for future reference as there will be tests later on that will go into these principles in detail.
1. Squash and Stretch: This principle states that as an object moves in certain ways it will squash and stretch depending on the forces being applied to it while it's moving. It's important to note that the shape retains it's mass and as it stretches in one direction it thins on the opposite axis. The most simple example of this is a ball as it hits a flat surface and bounces.
2. Anticipation: This means prepaing the audience for the action that is about to occur, for example a dancer jumping off of a platform would bend their knees and a golfer would raise a golf club up above their head before swinging. Removing the anticipation creates gag moments where an action occurs without the audience expecting what comes next.
3. Staging: Staging is the idea that the idea and meaning of what is happening on screen is unmistangly clear what is happening and what is going to occur. This is akin to staging on theatre and film.
4. Straight Ahead Action and Pose to Pose: These are animating techniques where Straight ahead action involves drawing subsequent drawings from an original frame, one after the other that creates a more fluid movement and makes for really good action sequences however it is hard to mantain proportions of an object over a number of drawings. Pose to pose involves drawing the key poses of an action and is a more planned out approach to animation that is more suitable for scenes with high drama.
5. Follow Through and Overlapping Action: These are elements that make an animation more realistic as it gives the impression that they adhere to the laws of physics. For instance as a character moves it may take a few frames for limbs and hair to catch up to the motion of the main body.
6. Slow In and Slow Out: This is the idea that objects accelerate and decelerate with any movement that they do, akin to a car starting and stopping. this applies to all motion as nothing can go from no mevement to full speed.
7. Arcs: Most human and animal movement occurs across arced trajectories, this should be applied to everything that moves from a joint such as arms and legs.
8. Secondary Action: Secondary actions are used to give actions more life. An example of a secondary action is a character who swings their arms as they walk or they whistle as they move, these actions need to compliment the primary action.
9. Timing: Timing in animation is the amount of frames given for an action that determines the speed of the film. Correct timing gives the impression of realism and can help flesh out the emotion of the character.
10. Exaggeration: Exaggeration is the act of making an animation look more alive by stretching movements or dimensions of a character as drawing the characters as like-like as possible creates a dull movement and can make an animation appear lifeless.
11. Solid Drawing: Solid drawing means drawing objects in a way that conveys three dimensions, giving the objects and characters weight and volume.
12. Appeal: Appeal in a character is akin to the charsima of an actor in that the characters have to appeal to an audience whether they make themselves out to be protagonists or the villian of the piece, the character has to be able to connect to the audience in order for the animation to be effective.