# Relationship between force of limiting friction and normal reaction These basically include terms like static friction, limiting friction, laws of friction, The ratio between the limiting friction force and the normal reactions between. To study the relationship between force of limiting friction and normal reaction. To find the co-efficient of friction between a block and a horizontal surface. The magnitude of the limiting force of friction is directly proportional to the normal reaction. If ' f ' is the magnitude of the limiting friction and N.

The graph shows that limiting friction F is directly proportional to the normal reaction R.

## What is Friction? Forces of Friction

It is an agreement with law of limiting friction. This experiment may be taken as a verification of the law. The constant ratio FIR, is called coefficient of friction p. It can be calculated by finding slope of the graph.

Precautions The surface table top should be horizontal. The thread part between block and pulley should be horizontal. Weight in pan should be increased in small steps and pan should not oscillate or rotate. Table top should be tapped gently each time.

Pulley should be friction less. Sources of error The table top may not be horizontal. The thread part between block and pulley may not be horizontal. Pulley may not be friction less. Read all the Articles 7. Every Article is a question. Why thread part between block and pulley is kept horizontal? It makes total weight of pan and weights effective in pulling the block horizontally. Why is pulley kept friction less? It is done to keep the weight of pan and weights in it to be fully effective. Friction in pulley will reduce its effective value.

Why roads become slippery after rains? Rain water forms a thin layer between our feet and road. It acts as a lubricant preventing interlocking of irregularities on the surface of wheel and road. Friction becomes less and causes slipping. Why brake surfaces are kept flat, though area of surface does not increase friction? Same force applied through more area reduces pressure. Most dry materials in combination give friction coefficient values from 0. It is difficult to maintain values outside this range.

### Friction - New World Encyclopedia

A value of 0. Rubber in contact with other surfaces can yield friction coefficients from 1. The coefficient of friction, when multiplied by the reaction force on the object by the contact surface, will give the maximum frictional force opposing sliding on the object. However, if the force pulling on the object is less than the maximum force of friction then the force of friction will be equal to the force pulling on the object.

You have to pull with a force greater than the maximum value of friction to move the object. Types of friction Frictional force in mechanics is the force which opposes the relative motion of an object. It is directed opposite to the motion of an object.

There are three types of frictional forces. Static friction is the friction acting on a body when the body is not in motion, but when a force is acting on it. Static friction is the same as the force being applied because the body isn't moving.

Static friction acts because the body tends to move when a force is applied on it. Limiting friction is the friction on a body just before it starts moving.

Generally, limiting friction is highest. Kinetic friction is the friction which acts on the body when the body is moving. Kinetic friction is usually smaller than limiting friction. The kinetic frictional force of a solid-solid interface is given by: The value of the coefficient depends upon the nature of the surfaces. The limiting friction is given by where R is the normal reaction force acting between the interface and the object and is the coefficient of limiting friction.

For a fluidthe frictional force is directly proportional to the velocity of the object. Static friction Static friction occurs when the two objects are not moving relative to each other like a book on a desk. The initial force to get an object moving is often dominated by static friction.

The static friction is in most cases higher than the kinetic friction. Examples of static friction: Rolling friction occurs when one object "rolls" on another like a car's wheels on the ground. This is classified under static friction because the patch of the tire in contact with the ground, at any point while the tire spins, is stationary relative to the ground.

### What is Friction? Forces of Friction

Limiting friction is the maximum value of static friction, or the force of friction that acts when a body is just on the verge of motion on a surface. 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.

From the mathematical point of view, however, the difference between static and kinetic friction is of minor importance: Since friction is always exerted in a direction that opposes movement, kinetic friction always does negative work. Examples of kinetic friction: Sliding 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 sliding friction Fluid friction is the friction between a solid object as it moves through a liquid or a gas. The drag of air on an airplane or of water on a swimmer are two examples of fluid friction. Reducing friction Devices Devices such as ball bearings or rollers can change sliding friction into much smaller rolling friction by reducing the points of contact on the object.

Techniques One technique used by railroad engineers is to back up the train to create slack in the linkages between cars. This allows the locomotive to pull forward and only take on the static friction of one car at a time, instead of all cars at once, thus spreading the static frictional force out over time.

Generally, when moving an object over a distance: