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COMMON FORCES IN MECHANICS

Contact Forces

Most of the Mechanical forces are contact forces

Normal reaction (R) is the perpendicular component of the contact force

The component parallel to the surfaces in contact is called

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Examples of Contact forces

Question

Choose the contact forces in the following

Answers

Upward bouyant force when a solid immersed in a fluid

Internal frictional forces like viscous force, air resistance and etc

Tension on a string as restoring force when it is stretched

The spring force, F = – k x , developed when it is extended or compressed

Fundamental forces such as Gravity, Electro Magnetic force, weak and strong Nuclear forces

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Facts of friction

Question 1

When there is no applied force, there is no static friction

Question 2

Friction is a necessary evil

Question 3

Kinetic Friction is a self adjusting force

Question 4

Rolling friction is greater than sliding friction

Hint

Ball bearings are used to reduce friction

Question 5

Frictional force is found to be independent of the area of contact

Static and Kinetic Friction

( fs)max = μsN is the limiting value of static friction

fk = μkN is the kinetic friction

μs is the coefficient of static friction  and μk the coefficient of kinetic friction

friction opposes impending motion

friction which opposes relative motion between the two surfaces in contact

The coefficient of friction  is greater than the coefficient of friction

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