# Curricular Unit:The Force of Friction

### Quick Look

Choose From: 2 lessons and 3 activities

Subject Areas: Measurement, Physical Science

### Summary

In the first of two lessons of this curricular unit, students are introduced to the concept of friction as a force that impedes motion when two surfaces are in contact. Student teams use spring scales to drag objects, such as a ceramic coffee cup, along a table top or the floor, measuring the frictional force that exists between the moving object and the surface it slides on. By modifying the bottom surface of the object, students find out what kinds of surfaces generate more or less friction. They also discover that both static and kinetic friction are involved when an object initially at rest is caused to slide across a surface. In the second lesson of the unit, students design and conduct experiments to determine the effects of weight and surface area on friction. They discover that weight affects normal friction (the friction that results from surface roughness), but for very smooth surfaces, the friction due to molecular attraction is affected by contact area.
This engineering curriculum aligns to Next Generation Science Standards (NGSS).

### Engineering Connection

Friction is involved in many aspects of skateboarding. For example, while the wheel bearings should produce little friction, enough friction is needed between the wheels and the floor to keep the board from skidding during tight turns.Engineers must understand how friction affects a wide range of situations as they design consumer products, such as ski bottoms in which friction is a disadvantage and hiking boots where friction provides traction.

### Educational Standards Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards. All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org). In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

###### NGSS: Next Generation Science Standards - Science
NGSS Performance Expectation

MS-PS2-2. Plan an investigation to provide evidence that the change in an object's motion depends on the sum of the forces on the object and the mass of the object. (Grades 6 - 8)

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This unit focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts
Plan an investigation individually and collaboratively, and in the design: identify independent and dependent variables and controls, what tools are needed to do the gathering, how measurements will be recorded, and how many data are needed to support a claim.

Alignment agreement:

Science knowledge is based upon logical and conceptual connections between evidence and explanations.

Alignment agreement:

The motion of an object is determined by the sum of the forces acting on it; if the total force on the object is not zero, its motion will change. The greater the mass of the object, the greater the force needed to achieve the same change in motion. For any given object, a larger force causes a larger change in motion.

Alignment agreement:

All positions of objects and the directions of forces and motions must be described in an arbitrarily chosen reference frame and arbitrarily chosen units of size. In order to share information with other people, these choices must also be shared.

Alignment agreement:

Explanations of stability and change in natural or designed systems can be constructed by examining the changes over time and forces at different scales.

Alignment agreement:

###### Common Core State Standards - Math
• Summarize numerical data sets in relation to their context, such as by: (Grade 6) More Details

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• Reporting the number of observations. (Grade 6) More Details

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• Describing the nature of the attribute under investigation, including how it was measured and its units of measurement. (Grade 6) More Details

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• Fluently add, subtract, multiply, and divide multi-digit decimals using the standard algorithm for each operation. (Grade 6) More Details

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### More Curriculum Like This

Factors Affecting Friction

Based on what students have already learned about friction, they formulate hypotheses concerning the effects of weight and contact area on the amount of friction between two surfaces.

Middle School Lesson
A Tale of Friction

High school students learn how engineers mathematically design roller coaster paths using the approach that a curved path can be approximated by a sequence of many short inclines. They apply basic calculus and the work-energy theorem for non-conservative forces to quantify the friction along a curve...

High School Lesson
Discovering Friction

With a simple demonstration activity, students are introduced to the concept of friction as a force that impedes motion when two surfaces are in contact. Then, in the associated activity, Sliding and Stuttering, they work in teams to use a spring scale to drag an object such as a ceramic coffee cup ...

Middle School Lesson
What Is Newton's First Law?

Students are introduced to the concepts of force, inertia and Newton's first law of motion: objects at rest stay at rest and objects in motion stay in motion unless acted upon by an unbalanced force. Students learn the difference between speed, velocity and acceleration, and come to see that the cha...

Middle School Lesson

### Assessment

Unit Summary Assessment: As a writing assignment or quiz, ask students to:

• define friction
• distinguish between static friction and kinetic friction
• explain why friction occurs
• describe common occurrences of friction, including those in which friction can be used to advantage in everyday life
• describe ways in which friction can be reduced
• describe how weight affects normal friction
• describe how surface area affects friction due to molecular attraction

### Contributors

Mary R. Hebrank, project writer and consultant, Pratt School of Engineering, Duke University

### Supporting Program

Engineering K-PhD Program, Pratt School of Engineering, Duke University

### Acknowledgements

This content was developed by the MUSIC (Math Understanding through Science Integrated with Curriculum) Program in the Pratt School of Engineering at Duke University under National Science Foundation GK-12 grant no. DGE 0338262. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

The lessons and associated activities of this curricular unit were originally published, in modified form, by Duke University's Center for Inquiry Based Learning (CIBL). Visit http://www.ciblearning.org/ for information about CIBL and other resources for K-12 science and math teachers.