NCERT 9TH CLASS SCIENCE CHAPTER FORCE AND LAWS OF MOTION


INTRODUCTION

 From our day to day experience, we all are familiar with the concept of 'Force'. While opening a door,  lifting a bucket or a bag, kicking a football or throwing a stone, we have to act differently and in many ways. We are either pushing or pulling the object.  No non-living object moves on its own. We have to apply the effort in the form of push or pull. This pull or push is called force. Thus a force is an      external agency that displaces or tends to displace a body from its position of rest. The direction in which the object is pushed or pulled is called the direction of the force. Force has both magnitude and direction. It is a vector quantity.
    

FORCE

    Force is the 'push' or 'pull' which can make a body move, stop a moving body, change the direction and speed of a moving body. Force cannot be seen but the effect of force on an object can be seen or felt. 

  
  Definition of Force 

    A force is physical quantity which causes or tends to cause a motion in an object at rest or changes or tends to change the direction of motion of a moving object or changes or tends to change the size and shape of an object or change or tends to change the speed of an object.

   Effect of force 

    A force produces the following effects :-

  1.   It can move or tend to move an object.
  2.   It can stop or tend to stop an object in motion.
  3.   It can change or tend to change the direction of motion of an object.
  4.   It can increase or decrease the speed of an object.
  5.   It can change the shape or size of an object.

TYPES OF FORCES

    Broadly speaking forces are classified as being of two types. (i) Contact force, (ii) Non-contact force
1.    Contact force : The force which act on a body either directly or through some connector are called contact forces. 
    Examples : Biological force, muscular force, mechanical force and frictional force are the examples of contact force. 
    (a) Muscular Force : This force produced by the muscles of living beings is called muscular force or biological force. 
    (b) Mechanical Force :  The force generated by machines are called mechanical force. 
    (c)  Friction Forc
Read More