"Wear and Tear" refers to the gradual damage or deterioration that inevitably takes place over time due to normal usage or aging of an item. This term is commonly used in the context of warranty contracts, where manufacturers generally state that damages arising from wear and tear are not covered. It's a form of depreciation that's expected to happen even when an item is used proficiently, cared for, and maintained properly.
For instance, the repeated impact of a hammer hitting nails causes unavoidable stress on the hammer's head. Even with careful use and maintenance, this stress accumulates over time, demonstrating wear and tear. However, this wear is considered normal and the hammer isn't expected to break beyond repair until it has undergone a significant amount of use.
Wear and tear is a practical manifestation of the second law of thermodynamics: over time, objects deviate from their original form and function (i.e., they have higher entropy) unless external energy is applied to maintain or, in some cases, restore them to their original condition.
In cases of certain items, known as consumables, restoration may not be possible. Parts intended to wear within a machine, like bearings or O-rings, are designed to be replaced over time. Similarly, consumable items such as paper, cardboard, and packaging are designed with a service lifespan that matches their intended use.
Long-lasting goods, like vehicles or musical instruments, are designed with replaceable wear parts. These goods are typically maintained through the replacement of these parts when required. A good way to determine if an item is durable is to establish if a service technician would typically attempt repairs on it.
Most warranties on durable goods limit coverage to a period where significant wear and tear is unlikely to severely impede the product's functionality. The length of a warranty can also be influenced by the customer's willingness to replace the product and the nature of the product itself. For instance, a screwdriver, which is a mass-produced consumable, would likely have a different warranty than a durable good.