## The kinetic friction coefficient

This experiment is conducted in two different parts; part A is the determination of the static friction coefficient whilst part B is the determination of the kinetic friction coefficient. In part A, after the apparatus are set up as shown in the diagram, the length of the wood plane used as the track is measured. Then, the plane is elevated gradually at one of its end. The plane is held still using a retort stand when the block rested on the plane is moving, in order to reduce the error in measuring the height of the elevated end of the plane from the desk surface. The experiment is then repeated by using different surfaces which were between glass/wood and wood/sand paper.

The value of the static friction coefficient is calculated by using the formula of = tan or by using the ratio of the height of the elevated end of the plane to the horizontal length of the plane. From the experiment, it can be determined that the static coefficient for wood surface with wood surface is 0.454, glass and wood is 0.315 while the sand paper surface with wood is 0.785. In part B, the kinetic friction coefficient is determined by using the acceleration of the object while it is moving. The acceleration is calculated by using the marks dotted onto a strip of ticker tape. The value of the coefficient is determined by using the formula of. From the experiment, it can be determined that the kinetic coefficient of wood surface with wood surface is 0.3290, glass surface with wood surface is 0.2390 and between the sand paper surface and wood surface is 0.4780.

Research question: Part A : What is the static friction coefficient of a certain surfaces that are in contact? Part B : What is the kinetic friction coefficient of a certain surfaces that are in contact? Hypothesis: Part A : The greater the coefficient, the rougher the surfaces. The coefficients are different between different surfaces. This is due to the fact that if the object is having bigger angle of inclination, it shows that the coefficient is bigger. Thus, it can be concluded that the surfaces are rougher.

Part B : The greater the coefficient, the rougher the surfaces. The coefficients are different between different surfaces. This is due to the fact that if the object is having bigger force to be applied in order to move it, it shows that the coefficient is bigger. Thus, it can be concluded that the surfaces are rougher. Basically, the hypothesis for both experiment are the same as the difference is only due to the static and the kinetic motion Theory:

In life, there is two types of friction; static friction and kinetic friction. Static friction has to be overcome by any objects in order to move. Once the object has already moved, it will experience kinetic friction. Both frictions have their own coefficient. Static frictional forces from the interlocking of the irregularities of two surfaces will increase to prevent any relative motion up until some limit where motion occurs. It is that threshold of motion which is characterized by the coefficient of static friction.

The coefficient of static friction is typically larger than the coefficient of kinetic friction. This is because when surfaces are in static contact, their microscopic hills and valleys can nestle down deeply into one another, thus forming a strong connection between the surfaces. The constant of proportionality is called, the coefficient of static friction. Kinetic friction is the friction encountered when surfaces slide against one another with a finite relative speed. The force generated by this friction, which will be designated with the symbol fk , acts to oppose the sliding motion at the point of contact between the surfaces.