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PBS
Wgbh: Peep and the Big Wide World: Steep and Steeper
Students explore what happens to a rolling object when the steepness of the ramp is increased.
PBS
Wgbh: Peep and the Big Wide World: Roll or Slide?
A classroom activity where students discover whether an object rolls, slides, or stays put.
Khan Academy
Khan Academy: What Is Friction?
Learn about the force of friction on this reference page which defines why friction is important and how it can change physic problems.