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Feedback Comments on Friction

by Ron Kurtus

A total of 120 comments and questions have been sent in. They are listed according to date.

You can read them to further your understanding of the subject.

List of next 10 letters




Friction Uses Does spreading of light have effect on air? India
Friction Start Rolling Why is rolling friction less than sliding friction? India
Friction Causes What is friction and wear rate? India
Friction What will happen if friction is not there? India
Coefficient of Friction Tables Coefficient of friction of turned die? India
Friction Equation Making a mobile home for Haiti earthquake USA
Friction Equation Friction is much less when object is on its edge India
Coefficient of Friction Tables Wants friction factorfor steel on steel and lithium grease Canada
Traction Why do tyres have treads? India
Friction Uses Is there any limit for friction? India

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First 10 letters

Does spreading of light have effect on air?

Topic: Friction Uses


September 18, 2010

does spreading of light has effect of air ?

vitrag - India



Light can heat up the air. Also, the air can disperse and spread out the light.

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Why is rolling friction less than sliding friction?

Topic: Friction Start Rolling


September 5, 2010

Explain how rolling friction is smaller than sliding friction?

Sheersa - India



With sliding friction, the surface on the ground is dragged along, resulting in the resistance of friction. However, with rolling friction, the point of the wheel on the ground is stationary and not sliding. As the wheel turns, the contact surface is picked up and a new contact surface is place in the ground. The friction is only a result of the surface being placed down and pulled up.

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What is friction and wear rate?

Topic: Friction Causes


August 30, 2010

what is friction,coefficient of friction,frictional force,frictional resistance & wear COF & wear rate or wt loss effected by roughness,smoothness & brittleness?

mayuri - India



Most of your questions are answered in our friction lessons. However, we do not have an information about wear rate.

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What will happen if friction is not there?

Topic: Friction


August 13, 2010

What will happen if friction is not there? Explain briefly.

Aninda - India



Others have asked this question and are seen in Answers to Readers Questions.

You could not walk or pick up a pencil without friction, because everything would slip. You could not even turn over in bed, because friction is needed to do that.

Friction is needed to keep things from sliding or slipping.

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Coefficient of friction of turned die?

Topic: Coefficient of Friction Tables


April 5, 2010


What is the coefficient of friction of turned(turning operation by lathe) die steel member?

surya - India



Since there are so many variables, you really need to experimentally determine the coefficient of friction in such a case.

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Making a mobile home for Haiti earthquake

Topic: Friction Equation


March 27, 2010

We design a mobile home(Single wide)for Haiti. We have to take in consideration earthquake.The mobile home will be resting on polished concrete pads (2' x 2') on the ground,to be located at each corner of the structure .The purpose of doing this is,that when an earthquake horizontal force acts against the structure.the pads on the ground will slide under the structure ,resulting in a minimal shear force(moment force).Resulting in no damage to the structure. The weight of the structure is 36,000.lbs.,the coeficient of kinetic friction of steel over concrete is .35.The horizontal displacement of an earthquake it is suppose to be less than 12 in.Want to know if we are right. Eng. Amador

Demetrio - USA



Many structures in earthquake zones are placed on rubber pads, which allow some give in the case of a tremor. See the articles:

However, considering having the home slide on a steel against concrete base may be a solution, assuming the horizontal ground motion is around 12".

Since I am sure there are many structural engineers versed in earthquake protection doing work in Haiti at this time, it would be good to get a professional's advise, especially if you are investing money in a project.

Best wishes on your work on the mobile home.

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Friction is much less when object is on its edge

Topic: Friction Equation


February 19, 2010

Dear Sir,

I have understood that the friction between two surfaces depends on the normal force and the coefficient of friction It is independent of area of contact. So a rectangular box will need the same force to slide along the longer or shorter sides on a marble floor. But if the box is tilted on the edge or a corner and pushed, much less force is needed meaning that the friction has reduced. ( Here only the area of contact is reduced - but reduced drastically) Why do we experience this as such? Can you please give me a scientific explanation? Thanks in advance.


Anand - India



Friction is due to a certain percentage of points on both surfaces being close to each other at an atomic level. In general, sliding friction is independent of the area of contact.

However, this is really an approximation. If you would measure the friction as you decrease the contact area, the friction would remain close to being constant. But there would be a point where the friction sudden decreased dramatically, such as when the contact area became close to being an edge.

The rule that friction does not vary with area is useful in common situations, but there are a number of situations where it fails.

Likewise, if you increase the normal force, there is a force where the friction would be much greater than expected.

The friction laws are a simplification of a highly complex physical phenomenon.

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Wants friction factorfor steel on steel and lithium grease

Topic: Coefficient of Friction Tables


October 29, 2009

Friction factor for steel sprayed with lithium grease on steel surface.

Does anyone have a friction factor for steel on steel coated with lithium grease?

Paul Salvian
Western Engineering Ltd.

Paul - Canada



I haven't seen any numbers for that combination. If somebody has such statistics, I can pass them on to you.

Typically, it is best to set up a small experiment and measure the coefficient of friction under the conditions that you use the materials. Often, values you see in charts do not apply to specific situations.

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Why do tyres have treads?

Topic: Traction


August 22, 2009

Why do shoes of the athletes are provided with spikes?

Why do cars, trucks and bulldozers have treated tyres?

natasha - India



Running shoes have spikes and tyres have treads to gain traction.

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Is there any limit for friction?

Topic: Friction Uses


August 10, 2009

is there any limit for friction

sanjeev - India



The coefficient of friction can range from zero to infinity. Sliding on ice can be close to zero friction. An object glued to the floor can have close to infinity friction.

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