Conditions for Producing Sliding Friction
There are several conditions people need to consider about. Firstly, the surface must be rough enough to let the object slide slowly and we can measure and do some experiments. Although there is no frictionless surface ever exist on the earth, scientists still have to find a place easy for them to study this research. Secondly, kinetic friction only occurs when two objects contact each other. During the same time, the moving energy toward two objects convert into heat energy. A typical example is that people rub hands to keep warm in the winter. Moreover, two objects are sliding on the surface of the other object. The direction of kinetic friction is against the direction of sliding motion and action point is on the object that is affected by it.
The Advantages and Disadvantages of Sliding Friction
Because friction work to prevent changing of the motion, so whether it is helpful or harmful depending on its situation. If people want to move something easier, it is harmful because they should use more strength to move that object. A way to reduce that force is to add a ball or wheel under that object, because at this time, rolling friction is less than kinetic friction. There are a lot of common examples to explain this statement such as cars we drive which have four wheels, large suitcases we use to travel which have two or four wheels, even huge trucks which have several rows of wheels to help reduce the force. Another way to reduce the friction is to change the materials of the surface. For instance, it is easier to move an object on the ice than on the wood because ice is smoother than wood. Moreover, in order to let machines and engines last longer, workers put oil on them, as a result they will not erode or damage very soon.
However, there is advantage of it is to help us to keep the original motion. Sometimes we need this kind of force to get a stationary motion, and we even have to increase the sliding force. When it is raining, the road becomes smoother, so smart people make wheels rougher like tyre tread to prevent cars slipping. When people are hiking, they wear special hiking shoes which use more rubber and add shoe prints to keep people steadily stand on rocks.
Experiment to Figure Out the Main Factors Affecting Sliding Friction
Scientists take three same slopes and three wooden blocks which have same shape and mass on a horizontal table, but they use different materials of surface such as glass, wood and sand and put them evenly on the slope. They use a spring dynamometer to measure the sliding friction to move the object at a constant speed. The greater the sliding friction, the rougher the surface. Consequently they can summarize that the coefficient has an influence. If scientists keep all the conditions except mass of the object and material of surface. This time they use objects that have different mass (various force between slope and block) and change the surface from various materials to the same. The result is that the greater the mass, the greater the sliding friction. In summary, two main factors influenced the kinetic friction are coefficient and the force between two objects.