Friction is an important force of nature that you deal with everyday. Friction affects the way you walk, your ability to pick up things and even your ability to drive down the street in your car. Friction is simply the resistant force between two objects moving while in contact with one another. But many people do not understand friction completely and are unaware that there are ways to increase the frictional force between two objects.
SmoothnessGenerally, the more surface contact two objects have, the less the friction between them will be. To increase frictional force between two objects you can make one or both of the object surfaces rougher. For example, it will take more energy to push a block of wood across a wooden tabletop if the block has been cut roughly on the side where it contacts the table. But if you sand down the block to make it relatively smooth, then the block will slide easier. This is because the roughness allowed for less surface contact between the two, which increased frictional force. This is not a universal rule, because two extremely smooth surfaces actually have increased friction because of electrostatic forces between them. Two plates of smooth glass, for example, do not glide across one another easily. WeightAdding weight to one object can significantly increase the frictional force between two moving objects. The more gravity presses the two surfaces together, the more friction exists and the harder it is to move them. The force of gravity will cause more pressure to press the objects together because of the weight of the object pressing down. The change in weight has to be to the object on top however. Consider the block of wood on a table idea again. If the block weighs one pound you could easily slide it across the table with one hand. Now imagine you added a 20-pound weight on top of the block. It would obviously take more energy to move it. This is because the force of friction between the two has increased. Stop MovementOne way to increase frictional force between to two objects is to take them out of motion. Static friction is a different type of friction that indicates the amount of energy required to set an object in motion instead of the energy needed to keep it moving along, which relates to kinetic friction. Static friction always requires more energy to start the object moving than it takes to keep it moving. Imagine pushing a car in neutral on a flat surface. Getting it started can be tough, but once it gets rolling, the momentum makes it much simpler to keep it rolling. This is similar to the theory of static friction. Remove LubricationOne way to reduce friction is to lubricate the surface so the objects slide against one another easily. With that in mind, it is reasonable to assume that taking away lubrication will increase the frictional force. It's true. Think about the wooden block on the table one more time. If the table were covered in motor oil, lubricating the entire surface, the block would slide very easily across the table. It would slide with minimal effort by the pusher. But spray off the table, cleaning up the mess entirely and try the same thing. You would see that it takes much more energy to push the block because the oil is no longer lubricating the surface.
