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- Depending upon the interaction between a force and an object, forces are classified a) Contact forces b) Non contact forces
- A force which can be applied only when it is in contact with an object is called a contact force.All mechanical forces are contact forces.
Following are the examples of contact force.
The force resulting due to action of muscles is known as muscular force. Muscular force can be applied only when it is in contact with the object. For ease a rope or handle may be used. e.g. We use muscular force to different activities using hands like lifting, throwing, catching etc. We use muscular force of animals to simplify our work. We use instruments with help of muscular force. i) cutting of vegetables or fruits using knife; ii) hammering of a nail; iii) kneading of dough; iv) bullocks ploughing in the field; v) horse pulling a cart.
The force of friction always acts on all the moving objects and its direction is always opposite to the direction of motion. It always act a point of contact of the two bodies. i.e. It arises due to contact between the two surfaces. e.g. When a vehicle is moving on a road, there is a force of friction between the surface of the road and tyre at point of contact. i) A ball rolling on a ground stops after some time; ii) When we stops pedaling a bicycle after some time distance it stops. iii) It is difficult to slide heavier objects on ground. iv) After sometime the tyres of vehicle wear and tear.
Types Of Contact Forces
- There are 6 kinds of forces which act on objects when they come into contact with one another. Remember, a force is either a push or pull.
A book resting on a table has the force of gravity pulling it toward the Earth. But the book is not moving or accelerating, so there must be opposing forces acting on the book. This force is caused by the table and is known as the normal force.
Applied force refers to a force that is applied to an object such as when a person moves a piece of furniture across the room or pushes a button on the remote control. A force is applied.
Frictional force is the force caused by relative motion of two surfaces that come into contact with each other.
Tension force is the force applied to a cable or wire that is anchored on opposite ends to opposing walls or other objects. This causes a force that pulls equally in both directions.
The spring force is the force created by a compressed or stretched spring. Depending upon how the spring is attached, it can pull or push in order to create a force.
The air resistance is a special type of frictional force that acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the motion of an object. This force will frequently be neglected due to its negligible magnitude (and due to the fact that it is mathematically difficult to predict its value). It is most noticeable for objects that travel at high speeds (e.g., a skydiver or a downhill skier) or for objects with large surface areas.
Non Contact Forces:
- A force which can be applied without any contact with two bodies is called a non contact force.Following are the examples of non contact force.
The force exerted by a magnet is called a magnetic force. e.g. Like poles of magnet repel each other , while unlike poles attract each other. These forces exist without a contact between the two magnets. e.g. i) Magnet attracts Cobalt, Nickel, Iron and steel towards itself. ii) When two magnets are brought near then South – south, North – north poles repel each other. While north and south pole attract each other.
The force exerted by a charged body is called a electrostatic force. e.g. Like charges repel each other , while unlike charges attract each other. These forces exist without a contact between the two bodies. e.g. i) When a comb is run through dry hair, then the comb can attract small pieces of paper.ii) If we bring a charged comb near our hair, they rise towards comb.iii) Charge is developed on synthetic fibre due to rubbing.iv) We can hear cracking sound of sparks when taking off or putting on woolen or synthetic clothes.
The force exerted by the earth on a body is called gravitational force. Actually this force exists between any two bodies in the universe.This force is always of attraction. e.g. When a body is dropped from a height it moves in downward direction towards the Earth with increasing speed (with constant acceleration). This constant acceleration by which all bodies fall down is called acceleration due to gravity. Its value is 9.8 m/s² (approx 10 m/s² )on the surface of the earth. e.g. i) A fruit from tree falls down;ii) Water falls down on a ground from a tap.iii) We feel the weight of bucket full of water holding in our hand.
- Region or space in which non contact force such as magnetic force, gravitational force, electrostatic force acts is called force field.
- The region surrounding a magnet, where magnetic substance experiences force is called the magnetic field.
- The region surrounding an electric charge, where electric charge experiences force is called the electric field.
- Thus a field is a sphere of influence of non contact force.
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