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.
Mechanical digestion occurs as layers of muscle in the stomach lining contract to produce a mixing and churning motion. Chemical digestion is carried out by stomach juices that contain enzymes and hydrochloric acid. When the food has been turned into liquid form, it moves onto the small intestine. 4.