Arc is a key factor of all animations due to the fact that it imp[lies for almost every action that is seen within a animation, such as arm and leg movement of the characters, the ark principle is also often used for the movement of objects that are thrown or are falling such as a football or even a bullet from a gun. Although you could argue that a bullet is more of a form of mechanical movement where the the object that is moving from above the ground is only moving in a straight line due to the fact that the conditions created that allow the object to move like that are produce by some sort of mechanism. Often when a object doesn’t go through the natural arc movement the movement of it is actual quite erratic and unpredictable.
Here are some excellent example of the Arc Principle:
Here are good example of the arc principle in action:
This example here is the Ultimate Spider-man when he jumps or swings Spider-man either arcs his arms or his swinging or jumping action is arc, you can see proof of this on the video if you watch all the random characters at the beginning or if you skip to 8:20.
Here is another example:
This example is a segment from the Star Wars: Rebels Movie Spark of the Rebellion called the Skirmish on Kessel, this short bit of footage shows a lot of the Arc Principle in action with the movement of the characters e.g. running and walking as well as Kananan swinging his lightsaber to deflect blaster bolts and Ezra jumping over a Stormtrooper with the Force, This clip makes an excellent example.
I have a piece of work that displays the animation principle of Arc, the Flour sac Animation the one I displayed for the first Principle of Animation Bounce, Squash and Stretch. The Flour Sack displays the arc principle when it jumps and when it is done this principle is displayed effectively and is easy to notice.