Force Force is a push or pull acting on an object.
Non-contact Force Forces that do not need physical contact with the object on which they are acting are called non-contact forces. Examples- Gravitational Force, Magnetic Force and Electrostatic Force etc.
Contact Force Forces that act on objects by direct or indirect physical contact with the objects are called contact forces. Examples- Applied Forces and Frictional Force are the examples of contact forces.
Static Friction Static friction is the friction that exists between stationary object and the surface.
Rolling Friction Rolling friction is the resistance offered by the surface to the motion of an object which rolls over it.
Sliding Friction Sliding friction refers to resistance created by two objects sliding against each other.
Fluid Friction The force of friction offered by the fluids (air and water) is called fluid friction. It is also called drag.
FORCE AND ITS EFFECTS
Force is a push or pull to an object. It has the following effects on the objects.
CONTACT FORCES- Forces that acts on objects by direct or indirect physical contact with the objects are called contact forces. Examples- Applied Forces and Frictional Force are the examples of contact forces.
The force which is applied on an object by a person or another object is called applied force.
When we do work with our hands like lifting weight, or pulling an object etc. we are applying force by using our muscles power.
Friction is the resistance to motion, experienced, when two surfaces in contact move with respect to each other.
Whenever the surface of one body moves over another, each exerts a force on the other which opposes the motion of the other. This is called frictional force.
Friction opposes the relative motion of the body as it always acts in the direction opposite to the direction of the motion of the object. For Example- if we gently give a push to a book lying on the table it stops after moving some distance. It means there is some force acting in opposite direction which stops the further movement of the book. This force is the force of friction which acts in the opposite direction of the motion.
CAUSES OF FRICTION
Any surface, however smooth, has lot of irregularities when seen under microscope, so when two such surfaces come in contact with each other and slide over each other, the irregularities gets interlocked with each other, which resists the motion of the surfaces. This leads to friction. On the rough surfaces, the number of irregularities are more hence friction offered by rough surface is also more than smooth surface.
Factors affecting Friction
TYPES OF FRICTION
The force required to overcome friction at the moment when an object starts moving from a position of rest is a measure of static friction. On the other hand, the force required to keep the object moving with the same speed is a measure of sliding friction.
When a box starts sliding, the contact points on its surface, do not get enough time to lock in to the irregularities. So the sliding friction is smaller than static friction.
When a body rolls over the surface of another body, the resistance to its motion is called rolling friction. Rolling reduces friction. It is always easier for a body to roll than to slide over another body or surface. That is why it becomes easy to pull luggage fitted with rollers beneath them.
Since rolling friction is less than sliding friction, so the sliding mechanism in most machines is replaced by rolling mechanism with the use of ball bearing to reduce the friction.
The above effectively means the following in terms of the magnitude of friction –
Static Friction > Sliding Friction >Rolling Friction
The force of friction offered by the fluids (air and water) is called fluid friction. It is also called Drag.
When car and airplanes move at high speeds, their motion is opposed by friction offered by air molecules surrounding them. This friction, which opposes the motion of a vehicle, produced by air is called drag. The same applies to ships and boats in water. To reduce drag, all automobiles, ships and airplanes are given a special shape, called a streamlined shape. A body with streamlined shape experiences minimum resistance when travelling through a fluid like air or water. Even sea animals like fish and shark, and Birds also have streamlined bodies which make it easier for them to move with great speeds.
ADVANTAGES AND DISADVANTAGES OF FRICTION
Methods of Reducing Friction
In some machines it is not advisable to use oil as a lubricant. In these cases, air cushion between moving parts are used to reduce friction.
Friction can never be entirely removed from a surface. No surface is perfectly smooth, some irregularities are always there even after polishing the surface.
Methods of Increasing Friction
Friction can be increased either by making surface rough or by increasing mass of the object that is moving on it.
Spring balance is a device used for measuring the force acting on an object. It consists of a coiled spring which gets stretched when a force is applied to it. Stretching of the spring is measured by a pointer moving on a graduated scale. The reading on the scale gives the magnitude of the force.
Some Interesting Facts