Friction is a complicated notion that is difficult to define in many instances, however it can be summed up as the force that resists motion of other objects. It is a force that occurs naturally without any human involvement, although humans can initiate its effects by trying to work against it. There are four different types of friction to consider: dry friction, fluid friction, lubricated friction, skin friction and internal friction. Dry friction occurs when two solid objects work against each other. An example of this would be rolling a ball and it stopping. In a friction-less environment it would just keep rolling, but due to friction it eventually stops (assuming no other forces keep pushing it). Fluid friction is essentially the same thing as dry friction except it applies to fluids of different densities working against each other. Lubricated friction is much like dry friction except a layer of fluid separates the two solids. A popular example of this is a slip and slide. The lubrication actually helps work against the friction when you are sliding down on your stomach with the water between your stomach and the slide. Skin friction refers to a solid moving through a liquid such as a boat having to propel itself through water.Although advantages and disadvantages to friction may manifest themselves in specific situations, they are not clearly defined. For example, one advantage to friction is that when you start your car and press the gas you do not keep going until you hit a wall. A disadvantage in the same respect is that you have to use a lot of gas to stop and start your car. It is very difficult to set clear boundaries on the advantages and disadvantages of friction because, like the example I used, a disadvantage might also be an advantage and vice-versa.