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Answers to Readers' Questions on Physical Science:

Friction

The following 106 comments and questions have been sent in. They are listed according to date.

List of first 10 items

• Force to make the sliding object remain in static position
• Why do erasers become dusty?
• Rolling resistance and frictional force on a wheel
• Why do tyres have treads?
• Why does carpet move when there is no friction on it?
• When does friction occur in swimming?
• Overcoming static and sliding friction
• Why is friction reduced when we lubricate?
• Friction in direction of motion
• Ways to avoid friction

Next 10

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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Why do erasers become dusty?

Question

October 9, 2009

why are erasers become dusty at times while rubbing

Shramona - India

18463

Answer

Erasers use friction to erase writing. If it is a chalk eraser, tiny pieces of the chalk are collected as dust. If it is a pencil eraser, parts of the erase break off and roll up the pencil writing to create a form of dust.

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Rolling resistance and frictional force on a wheel

Question

August 25, 2009

Do the driving wheels (drive from engine) of the automobile have rolling resistance other than frictional force which helps to propel the vehicle.?
Rolling resistance = mu*w (driven wheel)
Frictional force = Tractional force (Driving wheel)
Is this frictional force is also = mu*w..?
please reply soon.......
Regards
karthik

KARTHIK - India

18199

Answer

When the engine puts a torque on the wheel, it is static friction that prevents the tire from slipping and moves the vehicle forward. In some cases, traction from tire trends helps the motion. Rolling friction is mainly a resistance to moving as the tire is rolling forward.

Static friction on the tire is Fr = mu*W, where W is the weight on the tire or wheel.

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Why do tyres have treads?

Question

August 22, 2009

Why do shoes of the athletes are provided with spikes?

Why do cars, trucks and bulldozers have treated tyres?

natasha - India

18182

Answer

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

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Why does carpet move when there is no friction on it?

Question

April 17, 2009

I am curious to learn why a hand-knotted woolen carpet (without any synthetic yarns used) weighing 5 kilos, laid on a wall-to-wall synthetic carpet moves almost one foot per one week, even without any friction on the upper carpet, and that too only in one direction (westward). Generally the static actions take place only if there is a friction between two objects. Please explain.

m - Netherland

17620

Answer

When there in pressure on the upper carpet, its fibers, as well are those of the lower carpet bent to the side. Usually, it is the synthetic carpet that is the culprit. When the pressure is relieved, the fibers bounce back all in one direction, moving the upper carpet a tiny fraction in one direction.

This process is repeated until you notice the shift in position.

We have a throw rug on a carpet that is always shifting away from where it is supposed to be. It is quite annoying.

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When does friction occur in swimming?

Question

March 22, 2009

Hi, I'm Scarlett and for school I am doing a project.
In my project I need to know when does friction occur in swimming.
Please respond as asap, my project is due on 3/26/09.
Sincerely,

Scarlett - USA

17486

Answer

When you are swimming, there is friction of the water against your skin. It is much smaller than the water resistance from the shape of your body plowing through the water.

Special swim suits were used in the Olympics to reduce the friction of water against the skin.

See the lesson on fluid friction at:
http://www.school-for-champions.com/science/friction_changing_fluid.htm
for more information.

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Overcoming static and sliding friction

Question

March 16, 2009

What can you use to help you overcome static and sliding friction?

- USA

17447

Answer

Lubrication is used to overcome friction. Usually a liquid like oil is used for lubrication, although water can lubricate too. (Ever slip on a wet floor?)

Also see:
http://www.school-for-champions.com/science/friction_changing_sliding_hard.htm

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Why is friction reduced when we lubricate?

Question

March 6, 2009

why is the friction reduced when we lubricate two things?

abhishek - India

17393

Answer

Friction is usually caused by the rubbing of solid materials together. A lubricant is usually a liquid (such as oil) that allows the materials to slide across each other. A liquid rubbing against itself has little friction.

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Friction in direction of motion

Question

March 3, 2009

1- (3)examples in which friction is in the diriction of motion.

2- If Coeffitient of static friction equal to 0.5
what is the largest acceleration that a car may active moving strieght horizantal road. Assume that the engine power is not limited.

Safa - Sultanat of Oman

17363

Answer

Friction is a resistance to motion and is usually in the opposite direction of motion. But in the case of a wheel being turned on its axis, the resistance on the ground is in the direction of motion of the axis, although it is opposite the motion of the outer surface of the wheel.

Static friction is proportional to the weight of the car. The torque on the wheel must not be so great to cause the wheel to spin. See:

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

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Ways to avoid friction

Question

January 5, 2009

i need 2 kno ways of avoidin and reducing friction in a vehicle. plz can u list and xplain them and give xamples 2.i'm reali grateful 4 ur support.

mercy - Nigeria

17054

Answer

Proper air pressure in tires reduces rolling friction.
Lubricating the axles with grease and the engine with oil also reduces the friction.

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