The 12 basic animations principles were introduced by Disney Animators Ollie Johnston and Frank Thomas in their 1981 book The Illusion of Life: Disney Animation. Based in the work of Disney from the 1930s onwards, the principles make an effort of producing more realistic animations; its main purpose is to produce and create the illusion of physical laws into characters. Following a recount of the principles (Vanhemert, 2014)
1. Timing and Spacing: The illusion of moving in object animation is created through Timing and spacing following the laws of physics. Timing refers to the number of frames in-between two poses. The spacing refers to how those individual frames are placed (hallucinationrain, 2014).

2. Squash and Stretch: The purpose of this principle is to give sense of weight and flexibility to drawn objects. It can be easily apply in a bouncing ball but also for more complex objects as human face musculature. The example shows how A is a ball bouncing with a rigid, non-dynamic movement. In example B the ball is "squashed" at impact, and "stretched" during fall and rebound(Ratner, 2013).

4. Ease-In and Ease-Out: All objects or persons which moves, comes to a stop. Therefore it needs to be a time for acceleration and deceleration. Without ease in and ease out or slow in slow out, movements become very unnatural and robotic (EVL, no date).

6. Arcs: Real-life objects normally moves in some type of arcing motion, and in animation following this ensure the animation is smooth and moves in a realistic way. An exception of it is mechanical movement which follows a straight line form (EVL, no date).

8. Solid Drawing: It means taking into account forms in three-dimensional space, like volume and weight,thinking about the balance and anatomy in a pose. Despite now animators not only relied in their drawings is important to have the drawing skill and undestand the basics concepts of it(EVL, no date).
9. Appeal: In character design it correspond to create thinking to connect with viewers feelings, making it interesting for the audience(Vanhemert, 2014).
10. Straight Ahead Action and Pose to Pose: Straight ahead means creating each pose in a linear approach, one animation after another. Pose to Pose is more methodical and recalls to create and action from the key poses(Ratner, 2013).
11. Secondary Action: Secondary actions gives a scene of life, and can help to support the main action. An example is a person walking -primary action- who can simultaneously swing his arms as a secondary action (Ratner, 2013).
12. Staging: It refers to the background and foreground prepared for placing the characters, lights, space, camera angle, etc.(Ratner, 2013).
Based in Principles of Animation, I did some examples of them in the folowing exercises:
References:
Ratner, P. (2013). 3-D human modeling and animation. 3rt edition. Wiley: John Wiley & Son.
hallucinationrain (2014). Principles of animation- exaggeration & timing [Online]. Available https://hallucinationrain.wordpress.com/2014/03/06/principles-of-animation-exaggeration-timing/. [Accessed:08th November 2014]
EVL (no date). Follow Through and Overlapping Action. Electronic visualization Laboratory, EVL [Online]. Available https://www.evl.uic.edu/ralph/508S99/contents.html [Accessed:08th November 2014]
Vanhemert, K. (2014) Disney's 12 principles of Animation. Wired [Online] Available http://www.wired.com/2014/05/12-principles-of-animation/ [Accessed:08th November 2014]
Vanhemert, K. (2014) Disney's 12 principles of Animation. Wired [Online] Available http://www.wired.com/2014/05/12-principles-of-animation/ [Accessed:08th November 2014]