This is a ringing that sets in after excessive noise exposure, such as in a rock concert (being too near the speakers) or the explosion of a firecracker. This excessive noise can cause injury to the ear, causing the ringing. The tinnitus will usually clear up on its own, and will last anywhere from minutes to hours.
Mechanical digestion is the actual physical break down of food into smaller pieces. One example of this is mastication (chewing) which occurs in the mouth by the teeth, which act to cut and grind food into smaller pieces. This makes them easier to later digest as it increases the SA of the food molecules.
Both mechanical digestion and chemical digestion are necessary for the digestion of foods and beverages into pieces and molecules that are small enough to be absorbed in the small intestine. Both types of digestion are important and complement each other in the digestive process. There are, however, significant differences in the two types of digestion. Mechanical digestion involves the process of physically breaking down the food into ever smaller parts. The major player in mechanical digestion is mastication, which is the act of chewing and using the teeth to break the food into pieces small enough to be swallowed into the esophagus.