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Physics in Context - 1st Edition

Chapter 4: Resistance

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4.1  Friction in Mechanical Systems

Newton's Second Law of Motion
Using the force of gravity exerted on a hanging mass, a string draped over a pulley can apply force to a cart riding on an "frictionless air track." This force F causes the cart of mass m to accelerate a according to Newton's Second Law, F = m a. Use this Java applet to collect "experimental data" from trials using different masses and different "photogate" positions on the track.

Newton's Second Law of Motion
This series of lessons from The Physics Classroom has a detailed explanation of Newton's second law, examples, and practice problems.

Using Newton's Second Law to Solve Problems
This site gives a 10-step method for solving problems in mechanical systems.

Sir Isaac Newton
This site provides detailed biographical information about Sir Isaac Newton’s impact on mathematics, physics, and religion.

This page defines static friction and kinetic friction between two surfaces, including links to videos illustrating these forces.

The Force of Friction
This page summarizes the force of friction, as it is dependent on the normal force, and gives typical coefficient of friction values for various surfaces.

This PhET applet simulates pushing of various masses with various forces, with one option including friction. (Uses HTML5.)

Science of Football: Newton’s Second Law of Motion
This short video segment (from a 10-part series) demonstrates how a NFL kicker uses Newton’s Second Law to send a football through the goalposts. For more like this, see link to “Science of NFL Football” videos.

4.2  Viscosity in Fluid Systems

This page has a discussion and examples of viscosity, as well as abbreviated biographies of Jean Louis Poiseuille, George Stokes, and Osborne Reynolds.

Types of Fluid Flow
This site contains a PowerPoint-style presentation on fluid flow, Bernoulli's equation, viscosity, Stokes law, and Poiseuille's law. [Frames 1-12]

Poiseuille's Law and Blood Flow
This page uses Poiseuille's equation to analyze the blood flow in the human body.

Effect of Aerodynamic Drag Forces
This page discusses and analyzes the effects of wind resistance on cyclists.

The Physics of a Curveball
This site discusses why drag effects on a baseball can make it curve, including links to some helpful videos.

Aerodynamic Drag Forces on Kites
This NASA site presents the equations and physics for calculating the drag and lift forces that make it possible to fly a kite. For your advanced students: Don't miss the link to the "Kite Modeler."

4.3  Resistance in Electrical Systems

Ohm's Law
This page from the Physics Classroom discusses the importance of applications of Ohm’s Law, including practice problems.

Resistor Color Code Calculator
This handy calculator will show the resistance for given color codes, or provide the color codes from a given resistance value, and indicate whether it matches one of the EIA standard values for three-, four-, or five-band resistors. A standard resistor color code table is also provided.

Ohm's Law
This chapter of the Lessons in Electric Circuits Volume 1: DC begins with a discussion of the relationship between current, voltage, and resistance, then presents the water pipe analogy. The latter half of the page covers more advanced topics.

Ohm’s Law Simulation
This PhET applet simulates an electric circuit with varying voltage and resistance. Explore the changing current. (Uses HTML5.)

Basics of Electronics
This site has an online text designed to teach troubleshooting skills required by IT and electronics specialists, starting with the basic circuit skills for our course, in the first five chapters.

Basic Car Audio Electronics
This site applies the series/parallel resistance formulas and calculators to the real-world problem of wiring multiple speakers in a car sound system, including a water-pump analogy to explain why too many speakers wired incorrectly can damage your amplifier.

Learning Objects for Electronics (Gateway Technical College)
This site has a large collection of excellent interactive Flash lessons on various topics in electronics, including practice problems in series/parallel resistances, from basic to advanced. Of particular significance to this chapter are those under the heading, “DC/AC I & II”

Series-Parallel DC Circuits
This site provides a textbook approach to calculating total resistances in combination series-parallel circuits.

Building Series-Parallel Resistor Circuits
This page discusses strategies for building series and parallel resistive circuits using solderless breadboards and terminal strips. At the end there are several links to practice worksheets.

4.4  Resistance in Thermal Systems

Heat Transfer Fundamentals
This site gives a series of pages discussing the basic theory behind thermal conductivity as a rationale for cooling electronics.

Basic Theory of Heat Transfer
This page presents the heat flow equation and relates thermal conductivity to thermal resistance or impedance, as it would be applied to various materials able to insulate or conduct heat energy from electronic devices.

Insulation Fact Sheet
This Department of Energy fact sheet provides information on insulation, how to calculate how much you need, how to install it, and so forth.

Thermal Conductivity for Common Materials
This page lists the thermal conductivity values for several common substances, in both SI and English units.

Thermal Properties of Brick/Masonry Walls
An in-depth discussion (pdf) of thermal resistance in brick and masonry walls.