### Friction

Resource:
Science Reasoning Center: Friction

Description:
This passage describes a complex set of three experiments exploring the effect of several variables upon the amount of friction experienced by a wooden block dragged across a surface. Data is presented in the form of three different data tables. Questions target a student's ability to understand the experimental design, to recognize the effect of one variable on another, to extrapolate from the provided data in order to predict the result of conducting additional trials, and to represent the data in the form of a graph.

This activity aligns with the three dimensions of the Next Generation Science Standards in the manner described below:

Disciplinary Core Ideas
 Force and Motion (HS-PS2.A.1): Newton's 2nd Law accurately predicts changes in the motion of macroscopic objects. Although not explicitly stated in this passage, in each of the three experiments outlined students are applying a result of Newton’s 2nd Law.  In all trials the ‘applied’ or pulling force is assumed to be equal to the frictional force.  This is true in each of the situations described since objects that are moving at a constant speed must have a net force of zero.  This result—which comes directly from Newton’s 2nd Law—is what allows the reader to make this assumption.

Crosscutting Concepts
 Cause and Effect: Cause and effect relationships can be suggested and predicted for complex natural and human designed systems by examining what is known about smaller scale mechanisms within the system. Three cause-effect relationships are explored in this passage.  The effect of increasing load on frictional force is investigated in experiment 1.  Experiment 2 considers the frictional effect of changing the surfaces that are in contact.  Finally, experiment 3 explores a relationship that—interestingly enough—surface area has no effect on frictional force!

Practices

Associated Reading from The Physics Classroom

Other Supporting Pages at The Physics Classroom:
• The Curriculum Corner: Balanced vs. Unbalanced Forces; Net Force Help Sheet; Recognizing Forces; Friction

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