[what the friction]

[Defining the Force of Friction]

[Koji ezaki][Block 2-4]

Table of Contents

Introduction 2Research Questions 4Hypothesis 4Materials 5Method

Claim 1 5 Claim 2 6 Claim 3 7

Results and Analysis Claim 1 8 Claim 2 10 Claim 3 13

Conclusion 15

IntroductionForces:

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1In physics, a push or pull created upon objects interacting with each other is called a force. There are multiple types of forces which are divided into two broad categories based on whether they are touching each other or not; contact force and action-at-a-distance force.

Normal Force:The normal force is the force created upon an object that is in contact with another stable object; can occur vertically or horizontally. For example, in a vertical situation, when a person is standing on the stool, the stool is exerting an upward force on the person in order to support the weight of the person. In a horizontal situation, if a ladder in being leaned against a wall, the wall is pushing back horizontally on the ladder. In either case, if the normal force is not strong enough to support the objects, the stool/wall would break letting the person/ladder to break through. The normal force can be calculated using the formula: Fn=ma ; m = mass, a = acceleration.

2Friction Force:Friction force is categorized in the contact forces as it is a force caused by surfaces of objects moving across each other or attempting to move across. In further detail, friction is a force caused by two surfaces being closely pressed together, causing intermolecular attractive forces between molecules of different surfaces. Friction opposes the motion of an object such as when a car pulls the brakes, it causes a force opposite of the direction of motion. The maximum amount of friction force that a surface can exert upon an object can be calculated using the formula: Ff=μ×Fn

Dynamic Friction (Also known as kinetic friction)

Two kinds of friction forces exist. Dynamic friction is the force of friction caused when an object is moving across a surface. For example, dynamic friction occurs when a book is sliding across a table as a result of a variable pushing it. The table gives resistance to the movement of the book. This is an example of dynamic friction because it results from a sliding motion of the book. Dynamic friction can be calculated using the formula is: Ff (kinetic)=μ (kinetic)×Fn

The symbol μ(kinetic) represents the coefficient of dynamic friction between the two surfaces. The values of μ provide a measure of the relative amount of adhesion or attraction of the two surfaces for each other. The more that surface molecules tend to adhere to each

1 "Friction." Force. N.p., n.d. Web. 27 Dec. 2016.2 "Types of Forces." Types of Forces. N.p., n.d. Web. 27 Dec. 2016

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other, the greater the coefficient values and the greater the friction force.

Static Friction The other kind of friction force is static friction. Static friction occurs when two surfaces are not moving across each other. Static friction results when the surface of two objects are at rest relative to one another and a force exists on one of the objects to set it into motion relative to the other object. For example, suppose you were to slightly push on a large box to move it across the floor. The box might remain in place. A static friction force exists between the surfaces of the floor and the box to prevent the box from being set into motion. The static friction force balances the force that you exert on the box such that the stationary box remains at rest. This relationship is shown as: Ff (static)≤μ (static)×Fn The symbol μ(static) represents the coefficient of static friction between the two surfaces. Like the coefficient of sliding friction, this coefficient is dependent upon the types of surfaces that are attempting to move across each other.

Velocity:

Velocity is a vector quantity, which means it has a magnitude and a direction; speed and direction in velocity’s case. Velocity is the rate of change in an object’s position. To calculate velocity, one must divide the change in distance by the change in time. Constant velocity is when an object moves the same number of units for the same time measurement; no acceleration.

Acceleration:

Acceleration is also a vector quantity. It is the measurement of change in velocity. To calculate acceleration, one must divide the change in velocity by the change in time.

Mass and Weight:3Mass is the amount of matter contained in a body, it is the constant quantity and does not change with the change of position or location. Weight is the force by which the earth attracts a body toward its centre; the force on the

3  "What Is the Difference between Weight and Mass?" Newtonian Mechanics - What Is the Difference between Weight and Mass? - Physics Stack Exchange. N.p., n.d. Web. 27 Dec. 2016.

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object which is offered by the gravity. Weight of the body is the variable quantity and changes with the change in position and location due to the acceleration of the gravity acting on it.

Research QuestionsClaim 1: To investigate whether the mass (normal force) of an object is affecting μ ,the coefficient of friction, in any way. To investigate, the mass of a friction block will be manipulated by adding masses to evaluate the value of μ.

Claim 2:To investigate whether the surface area (interacting surface of contact) in objects in different types of surfaces changes the friction force. To investigate, the surface area of a friction block will be manipulated to evaluate the friction force.

Claim 3:To investigate whether the coefficient of static friction is greater than the coefficient of dynamic friction. To investigate, the static and dynamic friction of a friction block will be measured to evaluate the difference between the two values.

HypothesisClaim 1:Research Hypothesis: If the mass of the friction block changes, the value of μ will not change because the force of friction is equal to the normal for multiplied by μ, meaning that it in independent.

Null Hypothesis: If the mass of the friction block changes, the value of μwill change.

Claim 2:Research Hypothesis: If the force of friction is measured on different types of surfaces, it will show differing results depending on how rough or smooth the object is. If the force of friction is measured in different surface areas interacting between objects, it will show the same results because by

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Claim 2: Flat Wood

Surface Friction Block Printing Paper Tape Table Cloth Newton Scale

Claim 3: Flat Wood

Surface Friction Block Newton Scale Scale Masses

o 200g x 2o 500g

changing the contact area because it is only changing how the force is concentrated.

Null Hypothesis: If the force of friction is measured on different types of surfaces, it will show the same results. If the force of friction is measured in different surface areas interacting between objects, it will show different results because the contact area is different in size.

Claim 3:Research Hypothesis: If the coefficient of friction on a friction block is measured, the coefficient of kinetic friction will be greater than the coefficient of static friction because it takes more effort for an object to start/stop moving then it does to continue moving.

Null Hypothesis: If the coefficient of friction on a friction block is measured, the coefficient of kinetic friction will be equal to the coefficient of static friction.

Null Hypothesis: If the coefficient of friction on a friction block is measured, the coefficient of kinetic friction will be smaller than the coefficient of static friction.

MaterialsClaim 1:

Flat Wood Surface Friction Block Newton Scale Scale Masses

o 200g x 2o 500g

MethodClaim 1:

1) Prepare a flat, clean and dry wood surface with at least 1 meter in length as a base for measuring the friction force.

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2) Measure the mass of the friction block on the scale and record finding in a table.

3) Correct the newton scale to start at zero (if not already) before using it, as it may cause error in findings.

4) Connect the friction block to the newton scale and pull at a constant velocity to measure the force of friction accurately. Record finding in a table.

5) Add 200 grams of mass to the friction block and pull the newton scale at a constant velocity. Record findings in a table.

6) Add 400 grams of mass to the friction block and pull the newton scale at a constant velocity. Record findings in a table. (Add 400 grams onto the friction block, not an additional 400 grams on top of the 200 grams)

7) Add 500 grams of mass to the friction block and pull the newton scale at a constant velocity. Record findings in a table. (Add 500 grams onto the friction block, not an additional 500 grams on top of the 400 grams)

8) Add 700 grams of mass to the friction block and pull the newton scale at a constant velocity. Record findings in a table. (Add 700 grams onto the friction block, not an additional 700 grams on top of the 500 grams)

9) Repeat steps 4-8 ten times to make up for human error; average of the recordings will be used to make a graph.

10) Analyze data and show reasons to accuracy and precision.

Claim 2:1) Prepare a flat, clean and dry wood surface with at least 1 meter in

length as a base for measuring the friction force.2) Correct the newton scale to start at zero (if not already) before using

it, as it may cause error in findings.3) Connect the wooden friction block to

the newton scale and pull Side A at a constant velocity to measure the force of friction accurately. Record finding in a table.

4) Connect the same wooden friction block to the newton scale and pull Side B at a constant velocity to measure the force of friction accurately. Record finding in a table.

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Side A

Side Side

5) Connect the same wooden friction block to the newton scale and pull Side C at a constant velocity to measure the force of friction accurately. Record finding in a table.

6) Wrap a sheet of printing paper around the friction block using tape to attach the ends.

7) Connect the paper wrapped friction block to the newton scale and pull Side A at a constant velocity to measure the force of friction accurately. Record finding in a table.

8) Connect the same paper wrapped friction block to the newton scale and pull Side B at a constant velocity to measure the force of friction accurately. Record finding in a table.

9) Connect the same paper wrapped friction block to the newton scale and pull Side C at a constant velocity to measure the force of friction accurately. Record finding in a table.

10) Wrap a table cloth around the friction block.11) Connect the cloth wrapped friction block to the newton scale

and pull Side A at a constant velocity to measure the force of friction accurately. Record finding in a table.

12) Connect the same cloth wrapped friction block to the newton scale and pull Side B at a constant velocity to measure the force of friction accurately. Record finding in a table.

13) Connect the same cloth wrapped friction block to the newton scale and pull Side C at a constant velocity to measure the force of friction accurately. Record finding in a table.

14) Repeat steps 3-13 five times to make up for human error; average of the recordings will be used to make a graph.

15) Analyze data and show reasons to accuracy and precision.

Claim 3:1) Prepare a flat, clean and dry wood surface with at least 1 meter in

length as a base for measuring the friction force.2) Measure the mass of the friction block on the scale and record finding

in a table.3) Correct the newton scale to start at zero (if not already) before using

it, as it may cause error in findings.4) Connect the friction block to the newton scale and slowly pull it until

the friction block starts moving in order to measure static friction. Record finding in a table.

5) Using the same mass, pull the newton scale at a constant velocity to measure the force of dynamic friction accurately. Record finding in a table.

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6) Add 200 grams of mass to the friction block and pull the newton scale slowly until the friction block starts moving in order to measure static friction. Record finding in a table.

7) Using the same mass, pull the newton scale at a constant velocity to measure the force of dynamic friction accurately. Record finding in a table.

8) Add 400 grams of mass to the friction block and pull the newton scale slowly until the friction block starts moving in order to measure static friction. Record finding in a table. (Add 400 grams onto the friction block, not an additional 400 grams on top of the 200 grams)

9) Using the same mass, pull the newton scale at a constant velocity to measure the force of dynamic friction accurately. Record finding in a table.

10) Add 500 grams of mass to the friction block and pull the newton scale slowly until the friction block starts moving in order to measure static friction. Record finding in a table. (Add 500 grams onto the friction block, not an additional 500 grams on top of the 400 grams)

11) Using the same mass, pull the newton scale at a constant velocity to measure the force of dynamic friction accurately. Record finding in a table.

12) Add 700 grams of mass to the friction block and pull the newton scale slowly until the friction block starts moving in order to measure static friction. Record finding in a table. (Add 700 grams onto the friction block, not an additional 700 grams on top of the 500 grams)

13) Using the same mass, pull the newton scale at a constant velocity to measure the force of dynamic friction accurately. Record finding in a table.

14) Repeat steps 4-13 ten times to make up for human error; average of the recordings will be used to make a graph.

15) Analyze data and show reasons to accuracy and precision.

Results and AnalysisClaim 1: Precision

Precision is a way to show how well the equipment was used and the quality of the experiment in getting results; how close or far the results was between the number of results. Shown in (± x).

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0.2294kg: ±0.06

0.54+0.55+0.61+0.57+0.53+0.55+0.54+0.56+0.52+0.5310

=5.510

=0.55

0.4294kg:±0.07

0.94+1.02+0.98+0.93+0.96+1.06+1.01+1.02+1.02+1.0610

=1010

=1

0.6294kg:±0.068

1.59+1.55+1.61+1.56+1.54+1.49+1.61+1.53+1.57+1.5310

=15.5810

=1.558

0.7294kg:±0.098

1.78+1.65+1.76+1.66+1.62+1.63+1.72+1.68+1.67+1.6510

=16.8210

=1.682

0.9294kg:±0.112

2.25+2.15+2.35+2.3+2.3+2.19+2.22+2.24+2.36+2.2610

=22.6210

=2.262

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Force of Friction on different weights0.2294 kg

0.4294 kg

0.6294 kg

0.7294 kg

0.9294 kg

0.54 0.94 1.59 1.78 2.250.55 1.02 1.55 1.65 2.15

0.61 0.98 1.61 1.76 2.350.57 0.93 1.56 1.66 2.30

0.53 0.96 1.54 1.62 2.300.55 1.06 1.49 1.63 2.19

0.54 1.01 1.61 1.72 2.220.56 1.02 1.53 1.68 2.24

0.52 1.02 1.57 1.67 2.360.53 1.06 1.53 1.65 2.26

The error in raw data are mostly due to human error of not being able to pull an object at a perfectly constant velocity to measure the precise coefficient of dynamic friction. Other possible factors of errors include the 3 dents in the wooden friction block the size of 0.9cm, 1.2cm, and 1.3cm in diameter, which may have caused for differing results. Also, the wooden surface used showed some adhesiveness, which may have caused error in the results.

Individual Coefficient Values:

0.2294 Kg : μ= Ffmg

= 0.550.2294×9.8

=0.24 0.4294 Kg : μ= Ffmg

= 10.4294×9.8

=0.24

0.6294 Kg : μ= Ffmg

= 1.5580.6294×9.8

=0.25 0.7294 Kg : μ= Ffmg

= 1.6820.7294×9.8

=0.24

0.9294 Kg : μ= Ffmg

= 2.2620.9294×9.8

=0.25

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μ=2−0.58.3−2

=0.24

Claim 2: Precision: Paper

Side A: ±0.018

(0.51 )+(0.53 )+(0.54 )+ (0.53 )+(0.53)5 =

2.645 =0.528

Side B:±0.012

(0.50 )+(0.52 )+(0.51 )+(0.52 )+(0.51)5 =

2.565 =0.512

Side C:±0.012

(0.52 )+(0.51 )+(0.53 )+(0.52 )+(0.51)5 =

2.595 =0.518

The error in raw data are mostly due to human error of not being able to pull an object at a perfectly constant velocity to measure the precise coefficient of dynamic friction. Also, the wooden surface used showed some adhesiveness, which may have caused error in the results.

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Side A Side B Side C

Average of Paper: ±0.008667

0.528+0.512+0.5183

=1.5583

=0.519333

Friction Force (newtons) on different surface areas

Side A Side B Side C

0.51 0.50 0.52

0.53 0.52 0.51

0.54 0.51 0.53

0.53 0.52 0.52

0.53 0.51 0.51

Precision: Wood

Side A:±0.026

(0.68 )+(0.65 )+(0.68 )+ (0.69 )+(0.68)5 =

3.385 =0.676

Side B:±0.026

(0.65 )+(0.64 )+ (0.66 )+(0.68 )+(0.64)5 =

3.275 =0.654

Side C:±0.02

(0.64 )+(0.67 )+(0.68 )+(0.66 )+(0.65)5 =

3.35 =0.66

The error in raw data are mostly due to human error of not being able to pull an object at a perfectly constant velocity to measure the precise coefficient of dynamic friction. Other possible factors of errors include the 3 dents in the wooden friction block the size of 0.9cm, 1.2cm, and 1.3cm in diameter on Side A, which may have caused for differing results. Also, the wooden surface used showed some adhesiveness, which may have caused error in the results.

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Side A Side B Side C

Average of Wood: ±0.012667

0.676+0.654+0.663

=1.993

=0.663333

Friction Force (newtons) on different surface areas

Side A Side B Side C

0.68 0.65 0.64

0.65 0.64 0.67

0.68 0.66 0.68

0.69 0.68 0.66

0.68 0.64 0.65

Precision: Towel

Side A:±0.02

(1.00 )+(0.97 )+(0.96 )+ (1.00 )+(0.97)5 =

4.95 =0.98

Side B:±0.03

(0.99 )+(0.94 )+ (0.95 )+(0.97 )+(0.95)5 =

4.85 =0.96

Side C:±0.02

(0.98 )+(0.99 )+(0.95 )+ (0.97 )+(0.96)5 =

4.855 =0.97

The error in raw data are mostly due to human error of not being able to pull an object at a perfectly constant velocity to measure the precise coefficient of dynamic friction. Also, the towel and wooden surface used showed some adhesiveness, which may have caused error in the results.

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Side A Side B Side C

Average of Towel: ±0.01

0.98+0.96+0.973

=2.913

=0.97

Friction Force (Newtons) on different surface areas

Side A Side B Side C

1.00 0.99 0.98

0.97 0.94 0.99

0.96 0.95 0.95

1.00 0.97 0.97

0.97 0.95 0.96

Claim 3:Friction Force Static (newton)

Friction Force dynamic (newton)

Friction Force Static (newton)

Friction Force dynamic (newton)

Friction Force Static (newton)

Friction Force dynamic (newton)

229.4 grams 229.4 + 500 grams 229.4 + 400 grams0.91 0.54 3.98 1.78 3.78 1.591.02 0.55 3.67 1.65 3.82 1.551.03 0.61 4.15 1.76 3.71 1.610.92 0.57 3.86 1.66 3.81 1.560.95 0.53 4.21 1.62 3.72 1.540.89 0.55 3.91 1.63 3.83 1.490.96 0.54 4.01 1.72 3.69 1.611.12 0.56 4.12 1.68 3.76 1.530.98 0.52 3.96 1.67 3.79 1.570.93 0.53 4.21 1.65 3.80 1.53229.4 + 200 grams 229.4 + 700 grams

Note:

The mass of the friction block is 229.4 grams.

2.56 0.94 5.12 2.252.34 1.02 4.96 2.152.13 0.98 4.72 2.352.36 0.93 4.63 2.302.15 0.96 4.58 2.302.38 1.06 4.84 2.192.48 1.01 4.92 2.222.31 1.02 4.65 2.242.21 1.02 5.03 2.362.25 1.06 5.05 2.26

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Paper Wood Towel

Surface Type

Precision: Dynamic Friction: (Refer to Pages 9 and 10)

Static Friction:

0.2294 Kg ±0.043

1.21+1.18+1.23+1.19+1.2+1.23+1.16+1.22+1.18+1.2310

=12.0310

=1.203

0.4294 Kg ±0.243

2.56+2.34+2.13+2.36+2.15+2.38+2.48+2.31+2.21+2.2510

=23.1710

=2.317

0.6294 Kg ±0 .049

3.48+3.46+3.46+3.53+3.48+3.45+3.51+3.49+3.47+3.4810

=34.8110

=3.481

0.7294 Kg ±0 .338

3.98+3.67+4.15+3.86+4.21+3.91+4.01+4.12+3.96+4.2110

=40.0810

=4.008

0.9294 Kg ±0.27

5.12+4.96+4.72+4.63+4.58+4.84+4.92+4.65+5.03+5.0510

=48.510

=4.85

The error in raw data are mostly due to human error of not being able to pull an object slow enough to measure the precise coefficient of static friction. Other possible factors of errors include the 3 dents in the wooden friction block the size of 0.9cm, 1.2cm, and 1.3cm in diameter, which may have caused for differing results. Also, the wooden surface used showed some adhesiveness, which may have caused error in the results.

Individual Coefficient Values:

0 .2294Kg :μ= Ffmg

= 1.2030.2294×9.8

=0.54 0.4294 Kg : μ= Ffmg

= 2.3170.4294×9.8

=0.55

0.6294Kg : μ= Ffmg

= 3.4810.6294×9.8

=0.56 0.7294 Kg : μ= Ffmg

= 4.0080.7294×9.8

=0.56

0.9294 Kg : μ= Ffmg

= 4.850.9294×9.8

=0.53

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ConclusionClaim 1: Investigation of an object’s masses’ influence on μ ,the coefficient of friction, showed that the mass of an object does not affect μ ,the coefficient of friction, in any way. This can be shown in the experiments conducted, as all the different masses experimented show very similar results.

Claim 2:Investigation of a surface areas’ influence on the friction force of different types of surfaces showed that the surface area of an object does not affect the friction force. However, the different types of surfaces interacting affects the friction force. This can be seen in the experiments conducted, as all the different surface areas show very similar results within its surface types; however, different surface types show very different results.

The surface area does not affect the friction force because although the number of atoms interacting between the surfaces are different, the concentration of weight per square unit is divided differently, causing the force of different surface areas within the types to be the same.

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μ= 5−09.1−0

=0.55

Claim 3:Investigation of the difference between static friction and dynamic friction showed that the coefficient of static friction is always greater than the coefficient of dynamic friction. This can be seen in the experiments conducted, as all the different masses’ coefficient of friction showed that static friction was greater. This is because an object requires more energy to start moving compared to continuing moving.

Overall Conclusion

Evaluation of the force of friction in the form of an experiment showed the strength of maximum control. The environment of the experiment being conducted was controlled in a way to not affect the way the experiment was conducted by excluding irrelevant variable; sources of errors. For example, the use of one flat smooth surface when pulling the friction block allowed for exclusion of bumpy surfaces and slight differences between surfaces when using multiple surfaces. However, weaknesses in the experiment did exist. For example, the quality of the friction block provided was not very high. It contained three dents of various sizes which may have accounted for some errors in the experiment. The largest weakness of this experiment is the low reliability of human capabilities. Multiple times in the experiments, the experimenter would be asked to pull the friction block at a constant velocity to measure the coefficient of dynamic friction or pull the friction block slow enough to measure the coefficient of static friction. However, a human is not capable of pulling slow enough at a microscopic level or conditioned to pull at a constant velocity. Hence, they have to roughly estimate a constant velocity or pull to the slowest of their capabilities, which does not always turn out to be accurate. When conducting this experiment, the use of a gadget programed to pull slowly and/or at a constant velocity should be prepared to lessen the effects of human errors.

Since the characteristic of friction force has been shown. The next question would be the effects of liquids on the force of friction.

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