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Answers to Readers' Questions on Physical Science:

Friction

The following 115 comments and questions have been sent in. They are listed according to date.

List of first 10 items

• How to calculate rolling friction
• What will happen if friction is not there?
• Can work by friction be constant?
• Rotating a 2600 lb obelisk
• Imagine that friction suddenly vanishes
• Effect of different surfaces on velocity
• What are the evils of friction?
• Factors in determining coefficent of friction on a lathe
• Do rolling and static friction occur at the same time?
• Force to make the sliding object remain in static position

Next 10

How to calculate rolling friction

Question

August 21, 2010

I want to know how to calculate rolling friction in the wheel and how the components are shown in it. also want to know the vector analysis for it

Mayur - India

20268

Answer

For information on the subject, see:
http://www.school-for-champions.com/science/friction_rolling.htm
and
http://www.school-for-champions.com/science/friction_rolling_tires.htm

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What will happen if friction is not there?

Question

August 13, 2010

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

Aninda - India

20236

Answer

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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Can work by friction be constant?

Question

July 31, 2010

can the work done by any kind of friction in any case be constant?

Richa - India

20163

Answer

Work = Force X Distance
However, the friction force varies with the coefficient of friction between materials and their normal force.
The answer is: no.

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Rotating a 2600 lb obelisk

Question

July 5, 2010

I am trying determine the force required to rotate a granite obelisk weighing 2600 lbs with a square base 20"x20" that sits on a 4'x4'granite base block. I plan to glue obelisk to base with 3m 5200 or 2part epoxy. I intend to use a Come-a-along and manpower to rotate obelisk about 5 degrees about its center. I'm counting on the lubricating fluid friction of 3m 5200 before setup to facilitate the rotation. The rotation is part of a locking scheme. Assuming the torque required is 2600x 10/12'=2165#-ft/3( for the come-along)=722#-ft. Now I need ballpark friction estimate. Can you help?

Rodger - USA

20016

Answer

It sounds like quite a project. It is very difficult to calculate the friction, since the coefficient of friction for the 3M 5000 is really unknown. I imagine it would be a very thin layer, such that there would still be some granite-on-granite friction.

Suppose the coefficient was 0.4. That means you would have to apply 940 lbs linear force to move the obelisk. A big problem can be to overcome the inertia of the weight, no matter what the friction is. Once you get it moving, it may be easier.

Since you are rotating the obelisk, you get a mechanical advantage in applying the torque. Guessing a a coefficient of 0.4, that would put your torque at 0.4*722 = 289 ft-lbs.

I don't know if that is valid. It may be just a wild guess. I guess you'll just have to give it a try to see what happens.

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Imagine that friction suddenly vanishes

Question

June 8, 2010

Imagine that friction suddenly vanishes. List ten situations how would life be affected?(as a project)

Iram - India

19868

Answer

You could not sit in your chair, because you could slide off. You could not walk, because you need friction to move forward. You could not hold a pencil.

There are many similar situations. I am sure you can think of them.

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Effect of different surfaces on velocity

Question

June 4, 2010

what is effect of different surfaces on velocity of a body?

- USA

19837

Answer

When an object is sliding or moving along some other surface, the types of surfaces determine the amount of friction between them. The greater the friction, the more the resistance is, thus slowing down the velocity.

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What are the evils of friction?

Question

May 21, 2010

this website was helpful in providing information about friction.I have some questions in mind:what are the evils of friction?how to increase and decrease friction?? pls reply soon as possible.

- UAE

19766

Answer

Friction can cause problems when you want machinery to run smoothly. It can also cause problems when it causes machinery to overheat. Pressure between objects and surface finish can increase friction, what lubrication can decrease friction.

Look at our other lessons on friction to learn more about it.

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Factors in determining coefficent of friction on a lathe

Question

April 8, 2010

thanks for ur repla.. abut the coefficient of friction of turned (turning by lathe) of die steel member?

can u tell the what are the variables effect the value?...
i really need this value to solve my peoblem...

i search in some of the visiting sites, in that they are given some times 0.75 value, in some of the sites 0.2 given.... what basis those values got..

pls send repla..
thank u sir

madduri - India

19516

Answer

The friction is a function of the force pushing the objects together, the surface roughness, the hardness of each material and their shapes. In some cases, temperature may come into play.

It is much better to perform a typical test run, simply measuring the force required to turn the lathe on the die steel member and the force pushing the two objects together. Divide the force to turn the lathe by the normal force on the objects to get the coefficient of friction. You can then see a true value.

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Do rolling and static friction occur at the same time?

Question

March 6, 2010

When a car moves forward, there is a static friction acting on the tire, because the tire is instantaneously in contact with the road. Once the rolling starts, there is a rolling friction acting on the tire. Does this mean the two types of friction act on the tire in the same time?

- USA

19339

Answer

Static friction at the point of contact helps cause the wheel to roll. Without it, the wheel could just slide. Rolling friction can be complete. With tires, there is also an effect in rolling friction caused by distorting a soft tire.

See: http://www.school-for-champions.com/science/friction_rolling.htm

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Force to make the sliding object remain in static position

Question

October 30, 2009

Will the frictional force takes place in both objects to make the sliding object remain in static position?

- India

18598

Answer

If the force pushing an object is less than the force of static friction, it will not slide. Once that resistance is overcome by sufficient force, the object will readily slide.

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