Sliding Motion

1
Sliding Motion

• Alexis Jaramillo, Chris Petrie, Elana Seiti

2
Various Terms

• Sliding the process of translating an object
  across a plane so that it maintains contact with
  the plane
• Friction the resistance of an object to movement
• Force of Static Friction the initial force
  necessary to get object into motion the force of
  molecular cohesion between two surfaces that are
  in contact before sliding begins typically 20
  greater than kinetic friction
• Force of Kinetic Friction the force required to
  keep an object that is moving into constant
  movement
• Coefficient of Static Friction dimensionless
  constant (?s) representing the amount of static
  friction between 2 surfaces
• Coefficient of kinetic friction magnitude of the
  force of kinetic friction between two surfaces
  (?k)

3
Formulas Used

• Force equals mass multiplied by acceleration
• Normal Force to the surface is equal to mass of
  the object multiplied by the acceleration pulling
  the object against the surface
• The standard unit for measuring force is Newtons
  (N) - One Newton is equal to 1 kilogram
  multiplied by 1 meter divided by seconds squared
• Force of Static Friction
  
• Force of Kinetic Friction
• Coefficient of Static Friction is equal to the
  static friction of the object divided by its
  normal force to the surface
• Coefficient of Kinetic Friction is equal to the
  kinetic friction of the object divided by its
  normal force to the surface

4
Variables and Constants

• Variables
• Surface Area of Object in Contact
• Mass of Object in Contact
• Surface Type of the in Contact
• Velocities at Which Force is Applied

• Constants
• Opposing Contact Surface
• Acceleration Due to Gravity
• Angle of Force

5
Experimental Design
Figure 1.
6
Data Tables
Data Table 1. Measured With Spring-Scale
Data Table 2. Measured With Force Sensor
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Static Force Contact Area Comparison
Graph 1.
8
Static Force Contact Area Comparison
Graph 2.
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Static Force Contact Area Comparison
Graph 3.
10
Analysis Graphs 1-3

• Because of the slopes with the lines, a
  relationship between the contact area and Static
  Force required is shown.
• Slightly more Static Force is required to set an
  object into motion when the contact area is
  greater.
• Wood Doubling Contact Area Required 1.33 Times
  More S. Force
• Fuzz Doubling Contact Area Required 1.11 Times
  More S. Force
• Due to lack of time and funding, a similar
  experiment could not be conducted with examining
  the kinetic forces. However, because the forces
  have similar properties, it can be hypothesized
  that a there would be a similar result.

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Static Force Different Masses Comparison
0.882
0.666
261.72
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Analysis Graph 4

• Because the lines slope, it can be established
  that there is a relationship between static
  force, and the mass of an object.
• As the mass increases, the Static Force required
  to move the object also increases.
• When the mass first doubled, the static force was
  about 1.53 times greater for the wood block, and
  1.48 times greater for the fuzz.
• As the lines seem like they could possibly be
  almost parallel, that would mean that the
  increase in static force for each mass would be
  the same only the starting force value would be
  different.
• It cannot be established if the relationship
  shown is linear, as there are not enough points
  to show anomalies in the data.

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Kinetic Force Different Masses Comparison
1.60
1.16
261.72
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Analysis Graph 5

• Because the lines slope, it can be established
  that there is a relationship between kinetic
  force, and the mass of an object.
• As the mass increases, the Kinetic Force required
  to move the object also increases.
• When the mass first doubled, the kinetic force
  was about 1.40 times greater for the wood block,
  and 1.26 times greater for the fuzz.
• As the lines seem like they could possibly be
  almost parallel, that would mean that the
  increase in kinetic force for each mass would be
  the same only the starting force value would be
  different.
• It cannot be established if the relationship
  shown is linear, as there are not enough points
  to show anomalies in the data.

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Static vs. Kinetic Force
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But how would you calculate the coefficients?

• To calculate of coefficients of kinetic and
  static friction for any object against a surface,
  the Normal Force must first be known.
• With this, the following formulas can be solved.

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Example Calculating the Normal Force

• Normal Force (n) is the force pushing up on the
  object, equal to the force pushing down due to
  gravity.
• n Mass (kg) Accelleration of Gravity (m/s²)
• Ex.
• Mass 130.86 g 0.13086 kg
• n 0.13086 9.8
• n 1.282428

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Example Calculating the Coefficients

• As an example, we found the kinetic and static
  force that it required to move the 130.86 g
  object over the plastic table.
• Static Force 1.032 Newtons
• Kinetic Force 0.83 Newtons
• Normal Force (From Previous Example) 0.13086
• µs 1.032 / 0.13086
• µs 7.886
• µk 0.83 / 0.13086
• µk 6.343

(Notice that the coefficient of static friction
is less than that of kinetic.)
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According to the textbook
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Thank You For Your Patience!

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