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.
Variables:
Part A;
Independent : The surface of the objects
Dependent : The value of the coefficient of the static friction
Constant : The surface of the plane/track
Part B;
Independent : The surface of the objects
Dependent : The value of the coefficient of the kinetic friction
Constant : The surface of the plane/track, the power supply.
Apparatus:
Wooden block, sand paper, glass block, time ticker, ticker tape, ac-power supply, wooden track, meter ruler, retort stand
Method:
Part A;
- A wooden plane is measured and a wooden block is positioned onto it.
- One of the ends is elevated gradually until the block starts to move.
- The vertical height is measured.
- The static coefficient is calculated by using the ratio of the vertical height to the horizontal height of the plane.
- The experiment is then repeated by altering the surfaces.
Part B;
- The apparatus in Part A is used in this portion of experiment.
- However, a set of time ticker is set up and a strip of ticker tape is attached to the block.
- In determining the kinetic coefficient, the acceleration of the block is needed and it is calculated from the dots marked on the ticker tape.
-
The coefficient is determined by using the formulae of.
Results and calculation:
Part A;
e.g; surfaces : wood / wood
Uncertainty;
e.g
Part B;
F = ma
mg sin - = ma
Through out the experiment, the angle of the elevation is fixed at 30.
Determination of the acceleration of the block;
e.g Surface; wood / wood
initial velocity, u = = cms-1
final velocity, v = = cms-1
acceleration, a = = = 2.11 cms-1
Determination of the kinetic coefficient;
e.g
=
= 0.3290
Discussion & evaluation:
- The roughness of the surface of the objects and the plane/track used in the experiment should be in even condition. Meaning the experimenter should check the roughness by touching the surfaces. For instance, in this experiment, a piece of sand paper is wrapped to the wooden block (to investigate the coefficient of the sand paper surface due to the plane surface which is wood). The sand paper should be the one that has not been used before. This is due to the fact that even though the sand paper can be used for many times, however the roughness is already not the same.
- There might be a very large range of the uncertainty of the height of the lifted end of the plane. This is due to the action of elevating the end of the plane which is done manually by the experimenter. As to reduce to error, the position of the plane when the object starts to slide is held still using a retort stand. This is done while taking the measurement of the height.
-
In determining the coefficient of the static friction, the formula of = tan can be used. Nevertheless, since the method used in this portion of experiment allows the experimenter to choose between two options which are either to use the above equation of to use the ratio of the height of the elevated end of the plane to the horizontal length of the plane. The experimenter choose to use the ratio as error is minimized, compared to the equation.
Conclusion:
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.
Contribution:
- I suggested to use the acceleration method to determine the kinetic friction
- I recorded the results obtained.
- I elevated the track.
References: