8 science friction

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Finish Line & Beyond

FRICTION

Factors Affecting Friction

Types of Friction

Reducing Friction

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Friction is the force resisting the relative lateral (tangential) motion of solid

surfaces, fluid layers, or material elements in contact.

Force of Friction

Friction is a force that is created whenever two surfaces move or try to move acrosseach other.

Friction always opposes the motion or attempted motion of one surface across

another surface.

Friction is dependant on the texture of both surfaces.

Friction is also dependant on the amount of contact force pushing the two

surfaces together (normal force).

Factors affecting Friction

Friction depends partly on the smoothness of the contacting surfaces, a greater force

being needed to move two surfaces past one another if they are rough than if theyare smooth. However, friction decreases with smoothness only to a degree; friction

actually increases between two extremely smooth surfaces because of increasedattractive electrostatic forces between their atoms. Friction does not depend on the

amount of surface area in contact between the moving bodies or (within certainlimits) on the relative speed of the bodies. It does, however, depend on the

magnitude of the forces holding the bodies together. When a body is moving over ahorizontal surface, it presses down against the surface with a force equal to its

weight, i.e., to the pull of gravity upon it; an increase in the weight of the bodycauses an increase in the amount of resistance offered to the relative motion of the

surfaces in contact.

Types of Friction

Static friction: - Static friction is friction between two solid objects that are notmoving relative to each other. For example, static friction can prevent an object from

sliding down a sloped surface. The coefficient of static friction, typically denoted ass, is usually higher than the coefficient of kineticfriction.An example of static friction is the force that prevents a car wheel from slipping as it

rolls on the ground. Even though the wheel is in motion, the patch of the tire incontact with the ground is stationary relative to the ground, so it is static rather thankinetic friction.

The maximum value of static friction, when motion is impending, is sometimesreferred to as limiting friction, although this term is not used universally.

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Kinetic friction:- Kinetic (or dynamic) friction occurs when two objects are moving

relative to each other and rub together (like a sled on the ground). The coefficient ofkinetic friction is typically denoted as k, and is usually less than the coefficient of

static friction for the same materials.

Kinetic friction is when two objects are rubbing against each other. Putting a

book flat on a desk and moving it around is an example of kinetic friction.

Fluid friction is the interaction between a solid object and a fluid (liquid or

gas), as the object moves through the fluid. The skin friction of air on anairplane or of water on a swimmer are two examples of fluid friction.

Reducing friction

Devices

Devices such as wheels, ball bearings, air cushion or roller bearing can change

sliding friction into a much smaller type of rolling friction. Many thermoplasticmaterials such as nylon, HDPE and PTFE are commonly used for low friction

bearings. They are especially useful because the coefficient of friction falls withincreasing imposed load.

Lubricants

A common way to reduce friction is by using a lubricant, such as oil, water, or

grease, which is placed between the two surfaces, often dramatically lessening thecoefficient of friction. The science of friction and lubrication is called tribology.

Lubricant technology is when lubricants are mixed with the application of science,especially to industrial or commercial objectives.

Energy of friction

According to the law of conservation of energy, no energy is destroyed due to

friction, though it may be lost to the system of concern. Energy is transformed fromother forms into heat.

When an object is pushed along a surface, the energy converted to heat is given by:

Eth = kFn (x) dx

Where

Fn is the normal force,k is the coefficient of kinetic friction,x is the coordinate along which the object transverses.

http://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Drag_%5C(physics%5C)#Parasitic_draghttp://en.wikipedia.org/wiki/Ball_bearinghttp://en.wikipedia.org/wiki/Thermoplastichttp://en.wikipedia.org/wiki/Nylonhttp://en.wikipedia.org/wiki/HDPEhttp://en.wikipedia.org/wiki/PTFEhttp://en.wikipedia.org/wiki/Lubricanthttp://en.wikipedia.org/wiki/Tribologyhttp://en.wikipedia.org/wiki/Conservation_of_energyhttp://www.excellup.com/http://www.excellup.com/http://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Drag_%5C(physics%5C)#Parasitic_draghttp://en.wikipedia.org/wiki/Ball_bearinghttp://en.wikipedia.org/wiki/Thermoplastichttp://en.wikipedia.org/wiki/Nylonhttp://en.wikipedia.org/wiki/HDPEhttp://en.wikipedia.org/wiki/PTFEhttp://en.wikipedia.org/wiki/Lubricanthttp://en.wikipedia.org/wiki/Tribologyhttp://en.wikipedia.org/wiki/Conservation_of_energyhttp://www.excellup.com/


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Summary

Friction opposes the relative motion between two surfaces in contact. It acts

on both the surfaces.

Friction depends on the nature of surfaces in contact.

For a given pair of surfaces friction depends upon the state of smoothness of

those surfaces.

Friction depends on how hard the two surfaces press together.

Static friction comes into play when we try to move an object at rest.

Sliding friction comes with play when an object is sliding over another.

Sliding friction is smaller than static friction.

Friction is important for many of our activities.

Friction can be increased by making a surface rough.

The sole of the shoes and the tyres of the vehicle are treaded to increase

friction.

The friction is sometimes undesirable.

Friction can be reduced by using lubricants.

When one body rolls over another body, rolling friction comes into play.Rolling friction is smaller than the sliding friction.

In many machines, friction is reduced by using ball bearings.

Fluid friction can be minimised by giving suitable shapes to bodies moving in

fluids.



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