In this lesson our instructor talks about friction. First he discusses normal force and friction. Then he talks about friction as an equation, direction o friction, static versus kinetic friction, and how to use static friction. He does some basic examples on frictions. Lastly, he talks about the wheel. Four complete example problems round up this lesson.
Friction changes depending on the two materials involved. Wood on rubber is different than wood on wood is different than wood on ice. (This idea is captured by our coefficient of friction: μ.)
Friction changes depending on how hard the two materials are pushed together. (This idea is captured by the normal force between the two materials: FN.)
Friction changes depending whether or not the two materials are already in motion relative to each other-static vs. kinetic. (This idea is captured by having two different coefficients of friction: μs and μk.)
Friction always opposes motion. Whatever direction the object has (the direction of →v), friction points the opposite way.
The formula for friction is
Ffric = μ·FN.
Kinetic friction is just a continual force of Ffric = μk ·FN, pointing opposite whatever the current direction of movement is.
Static friction is a little different. It opposes the force on the object until it is overcome, at which point it switches to kinetic friction. It can cancel out other forces, but it never exceeds them.
MaximumStaticFriction = μs ·FN.
As usual, be careful when figuring out where all the forces go. A good free-body diagram goes a long, long way. And be extra careful when figuring out the normal force!
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
This book includes a set of features such as Analyzing-Multiple-Concept Problems, Check Your Understanding, Concepts & Calculations, and Concepts at a Glance. This helps the reader to first identify the physics concepts, then associate the appropriate mathematical equations, and finally to work out an algebraic solution.