Module 23: Introduction – Coulomb Friction

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From the course by Georgia Institute of Technology

Applications in Engineering Mechanics

324 оценки

Georgia Institute of Technology

Applications in Engineering Mechanics

324 оценки

This course applies principles learned in my course “Introduction to Engineering Mechanics” to analyze real world engineering structures. You will need to have mastered the engineering fundamentals from that class in order to be successful in this course offering. This course addresses the modeling and analysis of static equilibrium problems with an emphasis on real world engineering systems and problem solving. --------------------------- Recommended Background: You will need to have successfully completed my earlier course “Introduction to Engineering Mechanics” in order to be successful in this course. --------------------------- The copyright of all content and materials in this course are owned by either the Georgia Tech Research Corporation or Dr. Wayne Whiteman. By participating in the course or using the content or materials, whether in whole or in part, you agree that you may download and use any content and/or material in this course for your own personal, non-commercial use only in a manner consistent with a student of any academic course. Any other use of the content and materials, including use by other academic universities or entities, is prohibited without express written permission of the Georgia Tech Research Corporation. Interested parties may contact Dr. Wayne Whiteman directly for information regarding the procedure to obtain a non-exclusive license.

From the lesson

Coulomb Friction and Belt Friction

In this section students will learn about coulomb friction and belt friction.

Module 23: Introduction – Coulomb Friction4:55

Module 24: Coulomb Friction (cont.)8:28

Module 25: Coulomb Friction (cont.)5:41

Module 26: Coulomb Friction (cont.)11:24

Module 27: Coulomb Friction (cont.)7:28

Module 28: Belt Friction5:29

Module 29: Belt Friction - Examples7:22

Meet the Instructors

Dr. Wayne Whiteman, PE
Senior Academic Professional
Woodruff School of Mechanical Engineering

Hi this is Module 23 of Applications in Engineering Mechanics.

We've come quite a ways in the course.

We've, we've, we done the review of

my earlier course, introduction to engineering mechanics.

We've looked at a number of different

Structural Applications, Frames and Machines both plane and

3d Trusses or, or Space Trusses and also

systems supported by cable system, cable support systems.

We've looked at graphing

the internal Shear Forces and Bending Moments for beams.

And now we're at the final block of instruction, where we

look at the Friction or Effects of Friction on Static Equilibrium.

So for today's learning outcomes, I'm

going to describe this concept of Coulomb friction.

And how and where friction acts on a rigid body.

we're going to graph the conditions for coulomb

friction in situations where our rigid body.

Does not slip and where it

experiences slipping and then finally we're going to explain the condition for

Coulomb friction when a rigid body is about to experience impending tip.

So first of all the con, concept of Coulumb friction which you hopefully

have seen before in the physics background that you have for this course.

if I have a, a body

[SOUND]

sitting by itself no forces acting left or right

the, the weight is down at the mass center.

And we see that the, the, the resultant normal forces acting up

through the center of the body to balance that weight for us.

Now, if I come along and I push on the body, then we see

that the, from, from the equilibrium equations

that the normal force is going up

the migra away from the center.

Hence at that time we also get a friction force which is tangent

to the surface down here, and

it's going to oppo, oppose the impending motion.

And that friction force if you recall from your earlier physics days,

is a function of both the surface material and the normal force.

And the way that we account for the

surface material is through something we call the coefficient

of friction, which is given the symbol mu.

So here's, here's the situation with impending slip.

I start off with no force being applied, my normal force

is in the center as I apply a force to push this.

What I'll see is my, my normal force migrates and I, I gain a friction force.

And that friction force gets larger and larger depending on

the force P that I push on the rigid body.

And so if I start with a, a, a push of let's say 1 Newton and increase it

to 2, 3, 4, 5.

Eventually I'm going to get to the point where I have

no more friction available to stop the system from moving.

And so let's say that's at 5 Newtons for our thought experiments and then all

of a sudden it's going to break free and it's going to start to, to slide.

And the friction will go down slightly at that, at that point.

So let's look over here on this graph.

As I pushed with one,

zero, one, two, three, four, all of a sudden I got to my max friction.

Which was equal to the coefficient of what we call static friction times N.

And then, once the system breaks free, once

that rigid body starts to slide, we find

experimentally, that the friction goes down slightly, and

that value is mu sub K times N.

Where mu sub K is the kinetic

friction constant for sliding motion. And so what we do is we idealize

this actual experimental graph to show it like I, I've shown over here on the left.

We have a no-slip zone, and a slip zone.

In the no-slip zone, the friction can be

anything from zero up to the maximum value.

it can achieve use of S times N and then it

breaks down once it starts slipping and we just made this

more sharp curve where the friction drops down

to kinetic friction coefficient times the normal force.

So that's, that's how we understand impeding slip.

Now let's look at Impending tip.

There will be cases when the friction is large enough so that, the friction back is

large enough so when I push on a, on, on, on, the body with a force

P, it will actually start to tip.

And so at that point, once it tips, the normal force

has migrated all the way over to the corner of our body.

And fa, fi, the friction must be in the

no-slip zone, so it's gotta be somewhere in between

zero and the maximum friction we can, we can

achieve, and the end obviously must act on the body.

So here, we can find we'll

find as we do example problems, at what point, if

we have enough friction, will the body experience impending tip.

And we'll do all this in future modules, as we

look at actual real world examples and I'll see you then.

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