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Friction: Investigation 3 –










This Investigation is designed to help you to answer the following Focus Questions:

  • What is the relationship between weight and frictional force? 
  • What is the relationship between the surface area of an object in contact with another surface and the frictional force between two surfaces? 

Note: These questions are located in your  SDR at the beginning and end of the Investigation.


As a class, read the Background(s) in Investigation 1. When finished, discuss the following concepts as a class:

  • Frictional force is the force that opposes motion between two surfaces.
  • Frictional force causes negative acceleration.
  • Velocity does not have an effect on frictional force.
  • Acceleration measures the change of speed of an object that is moving is a specific direction.
  • All objects accelerate towards the earth at 9.8 m/s2.
  • Acceleration due to gravity is 9.8 m/s2.


The following list includes the one new Key Term that is introduced in the Investigation Background(s). It should be used, as appropriate, by teachers and students during everyday classroom discourse.

  • force

Note: The definitions of this term can be found on the Introduction page to the CELL.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.


  • Review your findings from Investigation Two.
    • Based on your experiments in Investigation Two, what is the relationship between frictional force and velocity? 
  • During this Investigation, you will be conducting more trials to determine whether or not two more factors influence frictional force.
  • You will conduct your trials using the same method as was used in Investigations One and Two.
    • During these trials, is it important that you pull the woodblock at the same velocity in each trial? No

Note: You should understand based on your conclusions after Investigation Two that frictional force does not depend on velocity. Although you had to maintain a constant velocity throughout a trial, the velocities between trials may differ slightly.

  • Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful in the lab.
  • After the video, divide into your lab group to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video. 


You should review the Investigation and video in preparation for the Lab.