Subject: Physics / General Physics
Question
Friction
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Peter Jeschofnig, Ph.D. Version 42-0262-00-01
LabReportAssistant
Thisdocumentisnotmeanttobeasubstituteforaformallaboratoryreport.TheLabReport Assistantissimplyasummaryofthe experiment’squestions, diagramsifneeded,anddatatables that shouldbeaddressedinaformallabreport.Theintentistofacilitatestudents’writingoflab reportsby providing this informationin an editable filewhichcan be sentto an instructor.
Observations
Massofblock: .419Kg Weight4.11N
DataTable 1:Flatboard
Flat Board
Force of KineticFriction,N
Force of StaticFriction,N
Trial 1
.8N
1.2N
Trial 2
.9N
1.4N
Trial 3
.9N
1.3N
Average
.87N
1.3N
Mass of block:.419 Kg Weight4.11 N
DataTable 2:FlatBoard- Block Sideways
Flat Board – Block
Sideways
Force of KineticFriction,N
Force of StaticFriction,N
Trial 1
.9N
1.4N
Trial 2
.9N
1.35N
Trial 3
.85N
1.4N
Average
.88N
1.38N
DataTable 3:DifferentSurfaces
Surfaces Tried: Glass Surface
Force of KineticFriction
Force of StaticFriction
Trial 1
.4N
.6N
Trial 2
.4N
.6N
Trial 3
.3N
.5N
Average
.37N
.57N
DataTable 4:DifferentSurfaces
Surfaces Tried:
Sandpaper
Force of KineticFriction
Force of StaticFriction
Trial 1
1.3N
1.7N
Trial 2
1.4N
1.8N
Trial 3
1.4N
1.7N
Average
1.37N
1.73N
DataTable 5:DifferentSurfaces
SurfacesTried:
Wood on Carpet
Force of KineticFriction
Force of StaticFriction
Trial 1
1.8N
2.4N
Trial 2
1.8N
2.4N
Trial 3
1.7N
2.3N
Average
1.77N
2.37N
DataTable 6:RaisedBoard
Height
BaseLength
?max
?s
Trial 1
25cm
61cm
22.3
.41
Trial 2
26cm
64cm
22.1
.41
Trial 3
25.5cm
63cm
22
.40
Average
25.5cm
62.67cm
22.1
.41
Calculations
1. Using the mass of the block and the average force of kinetic friction from Data Table 1, calculate the coefficient of kinetic friction from Equation 1:
Ffr(k) = uk FN. Thereforemk = Ffr(k) / FN
.87N= uk (4.11N)
uk= .87N/4.11N
uk= .211N
2. Using the mass of the block and the average force of kinetic friction from Data Table 2, calculate the coefficient of kinetic friction for the wood block sliding on its side. Record your results and see how it compares with the value of Uk obtained
from Data Table 1.
Uk = Ffr(k) / FN
Uk= .88N/ 4.11N
Uk= .214N
It is very similar, which leads me to conclude that sliding friction is proportional to the mass of an object, not the surface area.
3. From the data in Data Table 3, 4, and 5, compute the coefficient of static friction,Us, for the
glass surface on wood, the sandpapered surface on wood, and wood on carpet, etc., from
each of your three trials. Calculate an average value of Us. Record your results in your own
data sheets.
Glass
Us = Ffr(s) / FN
Us= .6N/4.11, 6.N/4.11N, .5N/4.11N
Us= .15N, .15N, .12N
Us average= .14
Sandpaper
Us = Ffr(s) / FN
Us= 1.7N/4.11N, 1.8N/4.11N, 1.7N/4.11N
Us= .41N, .44N, .41N
Us average= .42N
Carpet
Us = Ffr(s) / FN
Us= 2.4N/4.11N, 2.4N/4.11N, 2.3N/4.11N
Us= .58N, .58N, .56N
Us average= .57N
4. From the data obtained in Data Table 6 calculateUs for wood on wood from each of your three
trials.
Us = tan ? = sin ? max/ cos ? max or Us = tan ? = height/base
Trial 1= tan 22.3=.41 or 25/61 = .41
Trial 2=tan 22.1= .41 or 26/64 =.41
Trial 3= tan 22= .40 or 25.5/63=.40
5. Calculate an average value ofUs. Record your result on the data sheet.
(.41+.41+.40)/3 = .41
Questions
A.Howdoesthecoefficientofstaticfriction comparewiththecoefficientofkineticfriction for
thesamesurfacesand areas?
The coefficient of static friction is always larger than kinetic friction for the same surfaces and areas. This is because it takes more force to get an object moving than to keep it moving.
B. Why is it importanttoreduce frictionduring the operationof machinery?
If you reduce friction during the operation of machinery you will increase the energy efficiency of the machine which will allow you to get more work done without having friction act against you.
C. How does grease or oilaffectthecoefficientof friction?
Oil and grease are used to decrease the friction between two objects. This allows machines to operate more efficiently by reducing energy lost.
Summary- Overall I conducted an experiment to find out how much friction different surfaces had sliding over each other, and also wanted to find out if it took more force to get something moving or keep it moving. I learned that it takes more force to start something moving than to keep it moving, and also learned friction is proportional to mass of an object and texture rather than surface area. I also learned about how to calculate what degree an object will break free of friction if I know the coefficient of static friction, and how to find the coefficient given the height and length of a ramp that a block starts moving on.
